mirror of
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Merge pull request #3 from rust-console/lokathor
Hello World book chapter and crate coverage
This commit is contained in:
Lokathor
GitHub
commit
d25f9be54f
|
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@ -1,11 +1,12 @@
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[package]
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name = "gba"
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version = "0.0.1"
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version = "0.1.0"
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authors = ["Lokathor <zefria@gmail.com>", "Ketsuban"]
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edition = "2018"
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license = "Apache2"
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license = "Apache-2.0"
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[dependencies]
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gba-proc-macro = "0.1.1"
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[profile.release]
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lto = true
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|
|
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@ -30,7 +30,7 @@ do this stuff.
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dots as well as other support files:
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* crt0.s
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* linker.ld
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* thumbv4-none-eabi.json
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* thumbv4-none-agb.json
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* build.rs
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5) Run `arm-none-eabi-as crt0.s -o crt0.o` to build the `crt0.s` into a `crt0.o`
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@ -38,7 +38,7 @@ do this stuff.
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`build.bat` file it's set to simply run every single time because it's a
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cheap enough operation.
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6) Build with `cargo xbuild --target thumbv4-none-eabi.json`
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6) Build with `cargo xbuild --target thumbv4-none-agb.json`
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* The file extension is significant, and `cargo xbuild` takes it as a flag to
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compile dependencies with the same sysroot, so you can include crates
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normally. Well, crates that can run inside a GBA at least (Which means they
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@ -47,7 +47,7 @@ do this stuff.
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helpful because it has debug symbols).
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7) Also you can patch up the output to be a "real" ROM file:
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* `arm-none-eabi-objcopy -O binary target/thumbv4-none-eabi/debug/gbatest target/output.gba`
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* `arm-none-eabi-objcopy -O binary target/thumbv4-none-agb/debug/gbatest target/output.gba`
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* `gbafix target/output.gba`
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8) Alternately, you can use the provided `build.bat` file (or write a similar
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|
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@ -1,4 +1,11 @@
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# Rust GBA Tutorials
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* [ch01](ch01.md)
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* [Introduction](introduction.md)
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* [Ch 0: Development Setup](ch0/index.md)
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* [Ch 1: Hello GBA](ch1/index.md)
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* [hello1](ch1/hello1.md)
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* [IO Registers](ch1/io_registers.md)
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* [The Display Control Register](ch1/the_display_control_register.md)
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* [Video Memory Intro](ch1/video_memory_intro.md)
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* [hello2](ch1/hello2.md)
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|
|
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126
book/src/ch0/index.md
Normal file
126
book/src/ch0/index.md
Normal file
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@ -0,0 +1,126 @@
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# Chapter 0: Development Setup
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Before you can build a GBA game you'll have to follow some special steps to
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setup the development environment. Perhaps unfortunately, there's enough detail
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here to warrant a mini-chapter all on its own.
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## Per System Setup
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Obviously you need your computer to have a working rust installation. However,
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you'll also need to ensure that you're using a nightly toolchain. You can run
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`rustup default nightly` to set nightly as the system wide default toolchain, or
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you can use a [toolchain
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file](https://github.com/rust-lang-nursery/rustup.rs#the-toolchain-file) to use
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nightly just on a specific project, but either way we'll be assuming nightly
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from now on.
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|
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Next you need [devkitpro](https://devkitpro.org/wiki/Getting_Started). They've
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got a graphical installer for Windows, and `pacman` support on Linux. We'll be
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using a few of their binutils for the `arm-none-eabi` target, and we'll also be
|
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using some of their tools that are specific to GBA development, so _even if_ you
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already have the right binutils for whatever reason, you'll still want devkitpro
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for the `gbafix` utility.
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* On Windows you'll want something like `C:\devkitpro\devkitARM\bin` and
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`C:\devkitpro\tools\bin` to be [added to your
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PATH](https://stackoverflow.com/q/44272416/455232), depending on where you
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installed it to and such.
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* On Linux you'll also want it to be added to your path, but if you're using
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Linux I'll just assume you know how to do all that.
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|
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Finally, you'll need `cargo-xbuild`. Just run `cargo install cargo-xbuild` and
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cargo will figure it all out for you.
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## Per Project Setup
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Now you'll need some particular files each time you want to start a new project.
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You can find them in the root of the [rust-console/gba
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repo](https://github.com/rust-console/gba).
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* `thumbv4-none-agb.json` describes the overall GBA to cargo-xbuild so it knows
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what to do. This is actually a somewhat made up target name since there's no
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official target name. The GBA is essentially the same as a normal
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`thumbv4-none-eabi` device, but we give it the "agb" signifier so that later
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on we'll be able to use rust's `cfg` ability to allow our code to know if it's
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specifically targeting a GBA or some other similar device (like an NDS).
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* `crt0.s` describes some ASM startup stuff. If you have more ASM to place here
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||||
later on this is where you can put it. You also need to build it into a
|
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`crt0.o` file before it can actually be used, but we'll cover that below.
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* `linker.ld` tells the linker more critical info about the layout expectations
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that the GBA has about our program.
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## Compiling
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Once you've got something to build, you perform the following steps:
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|
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* `arm-none-eabi-as crt0.s -o crt0.o`
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* This builds your text format `crt0.s` file into object format `crt0.o`. You
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don't need to perform it every time, only when `crt0.s` changes, but you
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might as well do it every time so that you never forget to because it's a
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practically instant operation.
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* `cargo xbuild --target thumbv4-none-agb.json`
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* This builds your Rust source. It accepts _most of_ the normal options, such
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as `--release`, and options, such as `--bin foo` or `--examples`, that you'd
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expect `cargo` to accept.
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* You **can not** build and run tests this way, because they require `std`,
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which the GBA doesn't have. You can still run some of your project's tests
|
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with `cargo test`, but that builds for your local machine, so anything
|
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specific to the GBA (such as reading and writing registers) won't be
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testable that way. If you want to isolate and try out some piece code
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running on the GBA you'll unfortunately have to make a demo for it in your
|
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`examples/` directory and then run the demo in an emulator and see if it
|
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does what you expect.
|
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* The file extension is important. `cargo xbuild` takes it as a flag to
|
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compile dependencies with the same sysroot, so you can include crates
|
||||
normally. Well, creates that work in the GBA's limited environment, but you
|
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get the idea.
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|
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At this point you have an ELF binary that some emulators can execute directly.
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This is helpful because it'll have debug symbols and all that, assuming a debug
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build. Specifically, [mgba 0.7 beta
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||||
1](https://mgba.io/2018/09/24/mgba-0.7-beta1/) can do it, and perhaps other
|
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emulators can also do it.
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|
||||
However, if you want a "real" ROM that works in all emulators and that you could
|
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transfer to a flash cart there's a little more to do.
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|
||||
* `arm-none-eabi-objcopy -O binary target/thumbv4-none-agb/MODE/BIN_NAME target/ROM_NAME.gba`
|
||||
* This will perform an [objcopy](https://linux.die.net/man/1/objcopy) on our
|
||||
program. Here I've named the program `arm-none-eabi-objcopy`, which is what
|
||||
devkitpro calls their version of `objcopy` that's specific to the GBA in the
|
||||
Windows install. If the program isn't found under that name, have a look in
|
||||
your installation directory to see if it's under a slightly different name
|
||||
or something.
|
||||
* As you can see from reading the man page, the `-O binary` option takes our
|
||||
lovely ELF file with symbols and all that and strips it down to basically a
|
||||
bare memory dump of the program.
|
||||
* The next argument is the input file. You might not be familiar with how
|
||||
`cargo` arranges stuff in the `target/` directory, and between RLS and
|
||||
`cargo doc` and stuff it gets kinda crowded, so it goes like this:
|
||||
* Since our program was built for a non-local target, first we've got a
|
||||
directory named for that target, `thumbv4-none-agb/`
|
||||
* Next, the "MODE" is either `debug/` or `release/`, depending on if we had
|
||||
the `--release` flag included. You'll probably only be packing release
|
||||
mode programs all the way into GBA roms, but it works with either mode.
|
||||
* Finally, the name of the program. If your program is something out of the
|
||||
project's `src/bin/` then it'll be that file's name, or whatever name you
|
||||
configured for the bin in the `Cargo.toml` file. If your program is
|
||||
something out of the project's `examples/` directory there will be a
|
||||
similar `examples/` sub-directory first, and then the example's name.
|
||||
* The final argument is the output of the `objcopy`, which I suggest putting
|
||||
at just the top level of the `target/` directory. Really it could go
|
||||
anywhere, but if you're using git then it's likely that your `.gitignore`
|
||||
file is already setup to exclude everything in `target/`, so this makes sure
|
||||
that your intermediate game builds don't get checked into your git.
|
||||
|
||||
* `gbafix target/ROM_NAME.gba`
|
||||
* The `gbafix` tool also comes from devkitpro. The GBA is very picky about a
|
||||
ROM's format, and `gbafix` patches the ROM's header and such so that it'll
|
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work right. Unlike `objcopy`, this tool is custom built for GBA development,
|
||||
so it works just perfectly without any arguments beyond the file name. The
|
||||
ROM is patched in place, so we don't even need to specify a new destination.
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And you're finally done!
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|
||||
Of course, you probably want to make a script for all that, but it's up to you.
|
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|
|
@ -1 +0,0 @@
|
|||
# ch01
|
||||
190
book/src/ch1/hello1.md
Normal file
190
book/src/ch1/hello1.md
Normal file
|
|
@ -0,0 +1,190 @@
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|||
# hello1
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||||
|
||||
Ready? Here goes:
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||||
|
||||
`hello1.rs`
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||||
|
||||
```rust
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#![feature(start)]
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||||
#![no_std]
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||||
|
||||
#[cfg(not(test))]
|
||||
#[panic_handler]
|
||||
fn panic(_info: &core::panic::PanicInfo) -> ! {
|
||||
loop {}
|
||||
}
|
||||
|
||||
#[start]
|
||||
fn main(_argc: isize, _argv: *const *const u8) -> isize {
|
||||
unsafe {
|
||||
(0x04000000 as *mut u16).write_volatile(0x0403);
|
||||
(0x06000000 as *mut u16).offset(120 + 80 * 240).write_volatile(0x001F);
|
||||
(0x06000000 as *mut u16).offset(136 + 80 * 240).write_volatile(0x03E0);
|
||||
(0x06000000 as *mut u16).offset(120 + 96 * 240).write_volatile(0x7C00);
|
||||
loop {}
|
||||
}
|
||||
}
|
||||
```
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||||
|
||||
Throw that into your project, build the program (as described back in Chapter
|
||||
0), and give it a run. You should see a red, green, and blue dot close-ish to
|
||||
the middle of the screen. If you don't, something already went wrong. Double
|
||||
check things, phone a friend, write your senators, try asking Ketsuban on the
|
||||
[Rust Community Discord](https://discordapp.com/invite/aVESxV8), until you're
|
||||
able to get your three dots going.
|
||||
|
||||
## Explaining hello1
|
||||
|
||||
So, what just happened? Even if you're used to Rust that might look pretty
|
||||
strange. We'll go over each part extra carefully.
|
||||
|
||||
```rust
|
||||
#![feature(start)]
|
||||
```
|
||||
|
||||
This enables the [start
|
||||
feature](https://doc.rust-lang.org/beta/unstable-book/language-features/start.html),
|
||||
which you would normally be able to read about in the unstable book, except that
|
||||
the book tells you nothing at all except to look at the [tracking
|
||||
issue](https://github.com/rust-lang/rust/issues/29633).
|
||||
|
||||
Basically, a GBA game is even more low-level than the _normal_ amount of
|
||||
low-level that you get from Rust, so we have to tell the compiler to account for
|
||||
that by specifying a `#[start]`, and we need this feature on to do that.
|
||||
|
||||
```rust
|
||||
#![no_std]
|
||||
```
|
||||
|
||||
There's no standard library available on the GBA, so we'll have to live a core
|
||||
only life.
|
||||
|
||||
```rust
|
||||
#[cfg(not(test))]
|
||||
#[panic_handler]
|
||||
fn panic(_info: &core::panic::PanicInfo) -> ! {
|
||||
loop {}
|
||||
}
|
||||
```
|
||||
|
||||
This sets our [panic
|
||||
handler](https://doc.rust-lang.org/nightly/nomicon/panic-handler.html).
|
||||
Basically, if we somehow trigger a panic, this is where the program goes.
|
||||
However, right now we don't know how to get any sort of message out to the user
|
||||
so... we do nothing at all. We _can't even return_ from here, so we just sit in
|
||||
an infinite loop. The player will have to reset the universe from the outside.
|
||||
|
||||
The `#[cfg(not(test))]` part makes this item only exist in the program when
|
||||
we're _not_ in a test build. This is so that `cargo test` and such work right as
|
||||
much as possible.
|
||||
|
||||
```rust
|
||||
#[start]
|
||||
fn main(_argc: isize, _argv: *const *const u8) -> isize {
|
||||
```
|
||||
|
||||
This is our `#[start]`. We call it `main`, but it's not like a `main` that you'd
|
||||
see in a Rust program. It's _more like_ the sort of `main` that you'd see in a C
|
||||
program, but it's still **not** that either. If you compile a `#[start]` program
|
||||
for a target with an OS such as `arm-none-eabi-nm` you can open up the debug
|
||||
info and see that your result will have the symbol for the C `main` along side
|
||||
the symbol for the start `main` that we write here. Our start `main` is just its
|
||||
own unique thing, and the inputs and outputs have to be like that because that's
|
||||
how `#[start]` is specified to work in Rust.
|
||||
|
||||
If you think about it for a moment you'll probably realize that, those inputs
|
||||
and outputs are totally useless to us on a GBA. There's no OS on the GBA to call
|
||||
our program, and there's no place for our program to "return to" when it's done.
|
||||
|
||||
```rust
|
||||
unsafe {
|
||||
```
|
||||
|
||||
I hope you're all set for some `unsafe`, because there's a lot of it to be had.
|
||||
|
||||
```rust
|
||||
(0x04000000 as *mut u16).write_volatile(0x0403);
|
||||
```
|
||||
|
||||
Sure!
|
||||
|
||||
```rust
|
||||
(0x06000000 as *mut u16).offset(120 + 80 * 240).write_volatile(0x001F);
|
||||
(0x06000000 as *mut u16).offset(136 + 80 * 240).write_volatile(0x03E0);
|
||||
(0x06000000 as *mut u16).offset(120 + 96 * 240).write_volatile(0x7C00);
|
||||
```
|
||||
|
||||
Ah, of course.
|
||||
|
||||
```rust
|
||||
loop {}
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
And, as mentioned above, there's no place for a GBA program to "return to", so
|
||||
we can't ever let `main` try to return there. Instead, we go into an infinite
|
||||
`loop` that does nothing. The fact that this doesn't ever return an `isize`
|
||||
value doesn't seem to bother Rust, because I guess we're at least not returning
|
||||
any other type of thing instead.
|
||||
|
||||
Fun fact: unlike in C++, an infinite loop with no side effects isn't Undefined
|
||||
Behavior for us rustaceans... _semantically_. In truth LLVM has a [known
|
||||
bug](https://github.com/rust-lang/rust/issues/28728) in this area, so we won't
|
||||
actually be relying on empty loops in any future programs.
|
||||
|
||||
## All Those Magic Numbers
|
||||
|
||||
Alright, I cheated quite a bit in the middle there. The program works, but I
|
||||
didn't really tell you why because I didn't really tell you what any of those
|
||||
magic numbers mean or do.
|
||||
|
||||
* `0x04000000` is the address of an IO Register called the Display Control.
|
||||
* `0x06000000` is the start of Video RAM.
|
||||
|
||||
So we write some magic to the display control register once, then we write some
|
||||
other magic to three locations of magic to the Video RAM. We get three dots,
|
||||
each in their own location... so that second part makes sense at least.
|
||||
|
||||
We'll get into the magic number details in the other sections of this chapter.
|
||||
|
||||
## Sidebar: Volatile
|
||||
|
||||
We'll get into what all that is in a moment, but first let's ask ourselves: Why
|
||||
are we doing _volatile_ writes? You've probably never used it before at all.
|
||||
What is volatile anyway?
|
||||
|
||||
Well, the optimizer is pretty aggressive some of the time, and so it'll skip
|
||||
reads and writes when it thinks can. Like if you write to a pointer once, and
|
||||
then again a moment later, and it didn't see any other reads in between, it'll
|
||||
think that it can just skip doing that first write since it'll get overwritten
|
||||
anyway. Sometimes that's right, but sometimes it's wrong.
|
||||
|
||||
Marking a read or write as _volatile_ tells the compiler that it really must do
|
||||
that action, and in the exact order that we wrote it out. It says that there
|
||||
might even be special hardware side effects going on that the compiler isn't
|
||||
aware of. In this case, the Display Control write sets a video mode, and the
|
||||
Video RAM writes set pixels that will show up on the screen.
|
||||
|
||||
Similar to "atomic" operations you might have heard about, all volatile
|
||||
operations are enforced to happen in the exact order that you specify them, but
|
||||
only relative to other volatile operations. So something like
|
||||
|
||||
```rust
|
||||
c.volatile_write(5);
|
||||
a += b;
|
||||
d.volatile_write(7);
|
||||
```
|
||||
|
||||
might end up changing `a` either before or after the change to `c`, but the
|
||||
write to `d` will _always_ happen after the write to `c`.
|
||||
|
||||
If you ever use volatile stuff on other platforms it's important to note that
|
||||
volatile doesn't make things thread-safe, you still need atomic for that.
|
||||
However, the GBA doesn't have threads, so we don't have to worry about thread
|
||||
safety concerns.
|
||||
|
||||
Accordingly, our first bit of code for our library will be a _newtype_ over a
|
||||
normal `*mut T` so that it has volatile reads and writes as the default. We'll
|
||||
cover the details later on when we try writing a `hello2` program, once we know
|
||||
more of what's going on.
|
||||
114
book/src/ch1/hello2.md
Normal file
114
book/src/ch1/hello2.md
Normal file
|
|
@ -0,0 +1,114 @@
|
|||
# hello2
|
||||
|
||||
Okay so let's have a look again:
|
||||
|
||||
`hello1`
|
||||
|
||||
```rust
|
||||
#![feature(start)]
|
||||
#![no_std]
|
||||
|
||||
#[cfg(not(test))]
|
||||
#[panic_handler]
|
||||
fn panic(_info: &core::panic::PanicInfo) -> ! {
|
||||
loop {}
|
||||
}
|
||||
|
||||
#[start]
|
||||
fn main(_argc: isize, _argv: *const *const u8) -> isize {
|
||||
unsafe {
|
||||
(0x04000000 as *mut u16).write_volatile(0x0403);
|
||||
(0x06000000 as *mut u16).offset(120 + 80 * 240).write_volatile(0x001F);
|
||||
(0x06000000 as *mut u16).offset(136 + 80 * 240).write_volatile(0x03E0);
|
||||
(0x06000000 as *mut u16).offset(120 + 96 * 240).write_volatile(0x7C00);
|
||||
loop {}
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
Now let's clean this up so that it's clearer what's going on.
|
||||
|
||||
First we'll label that display control stuff:
|
||||
|
||||
```rust
|
||||
pub const DISPCNT: *mut u16 = 0x04000000 as *mut u16;
|
||||
pub const MODE3: u16 = 3;
|
||||
pub const BG2: u16 = 0b100_0000_0000;
|
||||
```
|
||||
|
||||
Next we make some const values for the actual pixel drawing
|
||||
|
||||
```rust
|
||||
pub const VRAM: usize = 0x06000000;
|
||||
pub const SCREEN_WIDTH: isize = 240;
|
||||
```
|
||||
|
||||
And then we want a small helper function for putting together a color value.
|
||||
|
||||
Happily, this one can even be declared as a const function. At the time of
|
||||
writing, we've got the "minimal const fn" support in nightly. It really is quite
|
||||
limited, but I'm happy to let rustc and LLVM pre-compute as much as they can
|
||||
when it comes to the GBA's tiny CPU.
|
||||
|
||||
```rust
|
||||
pub const fn rgb16(red: u16, green: u16, blue: u16) -> u16 {
|
||||
blue << 10 | green << 5 | red
|
||||
}
|
||||
```
|
||||
|
||||
Finally, we'll make a function for drawing a pixel in Mode 3. Even though it's
|
||||
just a one-liner, having the "important parts" be labeled as function arguments
|
||||
usually helps you think about it a lot better.
|
||||
|
||||
```rust
|
||||
pub unsafe fn mode3_pixel(col: isize, row: isize, color: u16) {
|
||||
(VRAM as *mut u16).offset(col + row * SCREEN_WIDTH).write_volatile(color);
|
||||
}
|
||||
```
|
||||
|
||||
So now we've got this:
|
||||
|
||||
`hello2`
|
||||
|
||||
```rust
|
||||
#![feature(start)]
|
||||
#![no_std]
|
||||
|
||||
#[cfg(not(test))]
|
||||
#[panic_handler]
|
||||
fn panic(_info: &core::panic::PanicInfo) -> ! {
|
||||
loop {}
|
||||
}
|
||||
|
||||
#[start]
|
||||
fn main(_argc: isize, _argv: *const *const u8) -> isize {
|
||||
unsafe {
|
||||
DISPCNT.write_volatile(MODE3 | BG2);
|
||||
mode3_pixel(120, 80, rgb16(31, 0, 0));
|
||||
mode3_pixel(136, 80, rgb16(0, 31, 0));
|
||||
mode3_pixel(120, 96, rgb16(0, 0, 31));
|
||||
loop {}
|
||||
}
|
||||
}
|
||||
|
||||
pub const DISPCNT: *mut u16 = 0x04000000 as *mut u16;
|
||||
pub const MODE3: u16 = 3;
|
||||
pub const BG2: u16 = 0b100_0000_0000;
|
||||
|
||||
pub const VRAM: usize = 0x06000000;
|
||||
pub const SCREEN_WIDTH: isize = 240;
|
||||
|
||||
pub const fn rgb16(red: u16, green: u16, blue: u16) -> u16 {
|
||||
blue << 10 | green << 5 | red
|
||||
}
|
||||
|
||||
pub unsafe fn mode3_pixel(col: isize, row: isize, color: u16) {
|
||||
(VRAM as *mut u16).offset(col + row * SCREEN_WIDTH).write_volatile(color);
|
||||
}
|
||||
```
|
||||
|
||||
Exact same program that we started with, but much easier to read.
|
||||
|
||||
Of course, in the full `gba` crate that this book is a part of we have these and
|
||||
other elements all labeled and sorted out for you. Still, for educational
|
||||
purposes it's often best to do it yourself at least once.
|
||||
10
book/src/ch1/index.md
Normal file
10
book/src/ch1/index.md
Normal file
|
|
@ -0,0 +1,10 @@
|
|||
# Ch 1: Hello GBA
|
||||
|
||||
Traditionally a person writes a "hello, world" program so that they can test
|
||||
that their development environment is setup properly and to just get a feel for
|
||||
using the tools involved. To get an idea of what a small part of a source file
|
||||
will look like. All that stuff.
|
||||
|
||||
Normally, you write a program that prints "hello, world" to the terminal. The
|
||||
GBA has no terminal, but it does have a screen, so instead we're going to draw
|
||||
three dots to the screen.
|
||||
33
book/src/ch1/io_registers.md
Normal file
33
book/src/ch1/io_registers.md
Normal file
|
|
@ -0,0 +1,33 @@
|
|||
# IO Registers
|
||||
|
||||
The GBA has a large number of **IO Registers** (not to be confused with CPU
|
||||
registers). These are special memory locations from `0x04000000` to
|
||||
`0x040003FE`. GBATEK has a [full
|
||||
list](http://problemkaputt.de/gbatek.htm#gbaiomap), but we only need to learn
|
||||
about a few of them at a time as we go, so don't be worried.
|
||||
|
||||
The important facts to know about IO Registers are these:
|
||||
|
||||
* Each has their own specific size. Most are `u16`, but some are `u32`.
|
||||
* All of them must be accessed in a `volatile` style.
|
||||
* Each register is specifically readable or writable or both. Actually, with
|
||||
some registers there are even individual bits that are read-only or
|
||||
write-only.
|
||||
* If you write to a read-only position, those writes are simply ignored. This
|
||||
mostly matters if a writable register contains a read-only bit (such as the
|
||||
Display Control, next section).
|
||||
* If you read from a write-only position, you get back values that are
|
||||
[basically
|
||||
nonsense](http://problemkaputt.de/gbatek.htm#gbaunpredictablethings). There
|
||||
aren't really any registers that mix writable bits with read only bits, so
|
||||
you're basically safe here. The only (mild) concern is that when you write a
|
||||
value into a write-only register you need to keep track of what you wrote
|
||||
somewhere else if you want to know what you wrote (such to adjust an offset
|
||||
value by +1, or whatever).
|
||||
* You can always check GBATEK to be sure, but if I don't mention it then a bit
|
||||
is probably both read and write.
|
||||
* Some registers have invalid bit patterns. For example, the lowest three bits
|
||||
of the Display Control register can't legally be set to the values 6 or 7.
|
||||
|
||||
When talking about bit positions, the numbers are _zero indexed_ just like an
|
||||
array index is.
|
||||
112
book/src/ch1/the_display_control_register.md
Normal file
112
book/src/ch1/the_display_control_register.md
Normal file
|
|
@ -0,0 +1,112 @@
|
|||
# The Display Control Register
|
||||
|
||||
The display control register is our first actual IO Register. GBATEK gives it the
|
||||
shorthand [DISPCNT](http://problemkaputt.de/gbatek.htm#lcdiodisplaycontrol), so
|
||||
you might see it under that name if you read other guides.
|
||||
|
||||
Among IO Registers, it's one of the simpler ones, but it's got enough complexity
|
||||
that we can get a hint of what's to come.
|
||||
|
||||
Also it's the one that you basically always need to set at least once in every
|
||||
GBA game, so it's a good starting one to go over for that reason too.
|
||||
|
||||
The display control register holds a `u16` value, and is located at `0x0400_0000`.
|
||||
|
||||
Many of the bits here won't mean much to you right now. **That is fine.** You do
|
||||
NOT need to memorize them all or what they all do right away. We'll just skim
|
||||
over all the parts of this register to start, and then we'll go into more detail
|
||||
in later chapters when we need to come back and use more of the bits.
|
||||
|
||||
## Video Modes
|
||||
|
||||
The lowest three bits (0-2) let you select from among the GBA's six video modes.
|
||||
You'll notice that 3 bits allows for eight modes, but the values 6 and 7 are
|
||||
prohibited.
|
||||
|
||||
Modes 0, 1, and 2 are "tiled" modes. These are actually the modes that you
|
||||
should eventually learn to use as much as possible. It lets the GBA's limited
|
||||
video hardware do as much of the work as possible, leaving more of your CPU time
|
||||
for gameplay computations. However, they're also complex enough to deserve their
|
||||
own demos and chapters later on, so that's all we'll say about them for now.
|
||||
|
||||
Modes 3, 4, and 5 are "bitmap" modes. These let you write individual pixels to
|
||||
locations on the screen.
|
||||
|
||||
* **Mode 3** is full resolution (240w x 160h) RGB15 color. You might not be used
|
||||
to RGB15, since modern computers have 24 or 32 bit colors. In RGB15, there's 5
|
||||
bits for each color channel stored within a `u16` value, and the highest bit is
|
||||
simply ignored.
|
||||
* **Mode 4** is full resolution paletted color. Instead of being a `u16` color, each
|
||||
pixel value is a `u8` palette index entry, and then the display uses the
|
||||
palette memory (which we'll talk about later) to store the actual color data.
|
||||
Since each pixel is half sized, we can fit twice as many. This lets us have
|
||||
two "pages". At any given moment only one page is active, and you can draw to
|
||||
the other page without the user noticing. You set which page to show with
|
||||
another bit we'll get to in a moment.
|
||||
* **Mode 5** is full color, but also with pages. This means that we must have a
|
||||
reduced resolution to compensate (video memory is only so big!). The screen is
|
||||
effectively only 160w x 128h in this mode.
|
||||
|
||||
## CGB Mode
|
||||
|
||||
Bit 3 is effectively read only. Technically it can be flipped using a BIOS call,
|
||||
but when you write to the display control register normally it won't write to
|
||||
this bit, so we'll call it effectively read only.
|
||||
|
||||
This bit is on if the CPU is in CGB mode.
|
||||
|
||||
## Page Flipping
|
||||
|
||||
Bit 4 lets you pick which page to use. This is only relevent in video modes 4 or
|
||||
5, and is just ignored otherwise. It's very easy to remember: when the bit is 0
|
||||
the 0th page is used, and when the bit is 1 the 1st page is used.
|
||||
|
||||
The second page always starts at `0x0600_A000`.
|
||||
|
||||
## OAM, VRAM, and Blanking
|
||||
|
||||
Bit 5 lets you access OAM during HBlank if enabled. This is cool, but it reduces
|
||||
the maximum sprites per scanline, so it's not default.
|
||||
|
||||
Bit 6 lets you adjust if the GBA should treat Object Character VRAM as being 2d
|
||||
(off) or 1d (on). This particular control can be kinda tricky to wrap your head
|
||||
around, so we'll be sure to have some extra diagrams in the chapter that deals
|
||||
with it.
|
||||
|
||||
Bit 7 forces the screen to stay in vblank as long as it's set. This allows the
|
||||
fastest use of the VRAM, Palette, and Object Attribute Memory. Obviously if you
|
||||
leave this on for too long the player will notice a blank screen, but it might
|
||||
be okay to use for a moment or two every once in a while.
|
||||
|
||||
## Screen Layers
|
||||
|
||||
Bits 8 through 11 control if Background layers 0 through 3 should be active.
|
||||
|
||||
Bit 12 affects the Object layer.
|
||||
|
||||
Note that not all background layers are available in all video modes:
|
||||
|
||||
* Mode 0: all
|
||||
* Mode 1: 0/1/2
|
||||
* Mode 2: 2/3
|
||||
* Mode 3/4/5: 2
|
||||
|
||||
Bit 13 and 14 enable the display of Windows 0 and 1, and Bit 15 enables the
|
||||
object display window. We'll get into how windows work later on, they let you do
|
||||
some nifty graphical effects.
|
||||
|
||||
## In Conclusion...
|
||||
|
||||
So what did we do to the display control register in `hello1`?
|
||||
|
||||
```rust
|
||||
(0x04000000 as *mut u16).write_volatile(0x0403);
|
||||
```
|
||||
|
||||
First let's [convert that to
|
||||
binary](https://www.wolframalpha.com/input/?i=0x0403), and we get
|
||||
`0b100_0000_0011`. So, that's setting Mode 3 with background 2 enabled and
|
||||
nothing else special.
|
||||
|
||||
However, I think we can do better than that. This is a prime target for more
|
||||
newtyping as we attempt a `hello2` program.
|
||||
113
book/src/ch1/video_memory_intro.md
Normal file
113
book/src/ch1/video_memory_intro.md
Normal file
|
|
@ -0,0 +1,113 @@
|
|||
# Video Memory Intro
|
||||
|
||||
The GBA's Video RAM is 96k stretching from `0x0600_0000` to `0x0601_7FFF`.
|
||||
|
||||
The Video RAM can only be accessed totally freely during a Vertical Blank
|
||||
(aka "vblank"). At other times, if the CPU tries to touch the same part of video
|
||||
memory as the display controller is accessing then the CPU gets bumped by a
|
||||
cycle to avoid a clash.
|
||||
|
||||
Annoyingly, VRAM can only be properly written to in 16 and 32 bit segments (same
|
||||
with PALRAM and OAM). If you try to write just an 8 bit segment, then both parts
|
||||
of the 16 bit segment get the same value written to them. In other words, if you
|
||||
write the byte `5` to `0x0600_0000`, then both `0x0600_0000` and ALSO
|
||||
`0x0600_0001` will have the byte `5` in them. We have to be extra careful when
|
||||
trying to set an individual byte, and we also have to be careful if we use
|
||||
`memcopy` or `memset` as well, because they're byte oriented by default and
|
||||
don't know to follow the special rules.
|
||||
|
||||
## RGB15
|
||||
|
||||
As I said before, RGB15 stores a color within a `u16` value using 5 bits for
|
||||
each color channel.
|
||||
|
||||
```rust
|
||||
pub const RED: u16 = 0b0_00000_00000_11111;
|
||||
pub const GREEN: u16 = 0b0_00000_11111_00000;
|
||||
pub const BLUE: u16 = 0b0_11111_00000_00000;
|
||||
```
|
||||
|
||||
In Mode 3 and Mode 5 we write direct color values into VRAM, and in Mode 4 we
|
||||
write palette index values, and then the color values go into the PALRAM.
|
||||
|
||||
## Mode 3
|
||||
|
||||
Mode 3 is pretty easy. We have a full resolution grid of rgb15 pixels. There's
|
||||
160 rows of 240 pixels each, with the base address being the top left corner. A
|
||||
particular pixel uses normal "2d indexing" math:
|
||||
|
||||
```rust
|
||||
let row_five_col_seven = 5 + (7 * SCREEN_WIDTH);
|
||||
```
|
||||
|
||||
To draw a pixel, we just write a value at the address for the row and col that
|
||||
we want to draw to.
|
||||
|
||||
## Mode 4
|
||||
|
||||
Mode 4 introduces page flipping. Instead of one giant page at `0x0600_0000`,
|
||||
there's Page 0 at `0x0600_0000` and then Page 1 at `0x0600_A000`. The resolution
|
||||
for each page is the same as above, but instead of writing `u16` values, the
|
||||
memory is treated as `u8` indexes into PALRAM. The PALRAM starts at
|
||||
`0x0500_0000`, and there's enough space for 256 palette entries (each a `u16`).
|
||||
|
||||
To set the color of a palette entry we just do a normal `u16` write_volatile.
|
||||
|
||||
```rust
|
||||
(0x0500_0000 as *mut u16).offset(target_index).write_volatile(new_color)
|
||||
```
|
||||
|
||||
To draw a pixel we set the palette entry that we want the pixel to use. However,
|
||||
we must remember the "minimum size" write limitation that applies to VRAM. So,
|
||||
if we want to change just a single pixel at a time we must
|
||||
|
||||
1) Read the full `u16` it's a part of.
|
||||
2) Clear the half of the `u16` we're going to replace
|
||||
3) Write the half of the `u16` we're going to replace with the new value
|
||||
4) Write that result back to the address.
|
||||
|
||||
So, the math for finding a byte offset is the same as Mode 3 (since they're both
|
||||
a 2d grid). If the byte offset is EVEN it'll be the high bits of the `u16` at
|
||||
half the byte offset rounded down. If the offset is ODD it'll be the low bits of
|
||||
the `u16` at half the byte.
|
||||
|
||||
Does that make sense?
|
||||
|
||||
* If we want to write pixel (0,0) the byte offset is 0, so we change the high
|
||||
bits of `u16` offset 0. Then we want to write to (1,0), so the byte offset is
|
||||
1, so we change the low bits of `u16` offset 0. The pixels are next to each
|
||||
other, and the target bytes are next to each other, good so far.
|
||||
* If we want to write to (5,6) that'd be byte `5 + 6 * 240 = 1445`, so we'd
|
||||
target the low bits of `u16` offset `floor(1445/2) = 722`.
|
||||
|
||||
As you can see, trying to write individual pixels in Mode 4 is mostly a bad
|
||||
time. Fret not! We don't _have_ to write individual bytes. If our data is
|
||||
arranged correctly ahead of time we can just write `u16` or `u32` values
|
||||
directly. The video hardware doesn't care, it'll get along just fine.
|
||||
|
||||
## Mode 5
|
||||
|
||||
Mode 5 is also a two page mode, but instead of compressing the size of a pixel's
|
||||
data to fit in two pages, we compress the resolution.
|
||||
|
||||
Mode 5 is full `u16` color, but only 160w x 128h per page.
|
||||
|
||||
## In Conclusion...
|
||||
|
||||
So what got written into VRAM in `hello1`?
|
||||
|
||||
```rust
|
||||
(0x06000000 as *mut u16).offset(120 + 80 * 240).write_volatile(0x001F);
|
||||
(0x06000000 as *mut u16).offset(136 + 80 * 240).write_volatile(0x03E0);
|
||||
(0x06000000 as *mut u16).offset(120 + 96 * 240).write_volatile(0x7C00);
|
||||
```
|
||||
|
||||
So at pixels `(120,80)`, `(136,80)`, and `(120,96)` we write three values. Once
|
||||
again we probably need to [convert them](https://www.wolframalpha.com/) into
|
||||
binary to make sense of it.
|
||||
|
||||
* 0x001F: 0b11111
|
||||
* 0x03E0: 0b11111_00000
|
||||
* 0x7C00: 0b11111_00000_00000
|
||||
|
||||
Ah, of course, a red pixel, a green pixel, and a blue pixel.
|
||||
15
book/src/introduction.md
Normal file
15
book/src/introduction.md
Normal file
|
|
@ -0,0 +1,15 @@
|
|||
# Introduction
|
||||
|
||||
Here's a book that'll help you program in Rust on the GBA.
|
||||
|
||||
It's very "work in progress". At the moment there's only one demo program.
|
||||
|
||||
## Other Works
|
||||
|
||||
If you want to read more about developing on the GBA there are some other good resources as well:
|
||||
|
||||
* [Tonc](https://www.coranac.com/tonc/text/toc.htm), a tutorial series written
|
||||
for C, but it's what I based the ordering of this book's sections on.
|
||||
* [GBATEK](http://problemkaputt.de/gbatek.htm), a homebrew tech manual for
|
||||
GBA/NDS/DSi. We will regularly link to parts of it when talking about various
|
||||
bits of the GBA.
|
||||
38
build.bat
38
build.bat
|
|
@ -1,32 +1,14 @@
|
|||
@echo off
|
||||
REM It could work to only rebuild the `crt0.o` file when `crt0.s` actually
|
||||
REM changes, but it's actually a super cheap operation so we'll just do it
|
||||
REM every single time to avoid any mix ups.
|
||||
@echo on
|
||||
|
||||
@rem Build the crt0 file before we begin
|
||||
arm-none-eabi-as crt0.s -o crt0.o
|
||||
|
||||
@echo off
|
||||
REM This builds our program for the GBA. Note that the extension here is
|
||||
REM important, because it causes all crates that we might import to also
|
||||
REM use the correct target.
|
||||
@echo on
|
||||
@rem Build all examples, both debug and release
|
||||
cargo xbuild --examples --target thumbv4-none-agb.json
|
||||
cargo xbuild --examples --target thumbv4-none-agb.json --release
|
||||
|
||||
cargo xbuild --target thumbv4-none-eabi.json
|
||||
|
||||
@echo off
|
||||
REM Some emulators can use cargo's output directly (which is cool, because then
|
||||
REM you can keep debug symbols and stuff), but to make a "real" ROM we have to
|
||||
REM also use the devkitpro tools to patch up the file a bit.
|
||||
@echo on
|
||||
|
||||
arm-none-eabi-objcopy -O binary target/thumbv4-none-eabi/debug/main target/output.gba
|
||||
gbafix target/output.gba
|
||||
|
||||
@echo off
|
||||
REM Now all the same for release mode too!
|
||||
@echo on
|
||||
|
||||
cargo xbuild --target thumbv4-none-eabi.json --release
|
||||
arm-none-eabi-objcopy -O binary target/thumbv4-none-eabi/release/main target/output-release.gba
|
||||
gbafix target/output-release.gba
|
||||
@echo Packing examples into ROM files...
|
||||
@for %%I in (.\examples\*.*) do @(
|
||||
echo %%~nI
|
||||
arm-none-eabi-objcopy -O binary target/thumbv4-none-agb/release/examples/%%~nI target/example-%%~nI.gba >nul
|
||||
gbafix target/example-%%~nI.gba >nul
|
||||
)
|
||||
|
|
|
|||
333
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<ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch0/index.html" class="active"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch1/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch1/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch1/io_registers.html"><strong aria-hidden="true">3.2.</strong> IO Registers</a></li><li><a href="../ch1/the_display_control_register.html"><strong aria-hidden="true">3.3.</strong> The Display Control Register</a></li><li><a href="../ch1/video_memory_intro.html"><strong aria-hidden="true">3.4.</strong> Video Memory Intro</a></li><li><a href="../ch1/hello2.html"><strong aria-hidden="true">3.5.</strong> hello2</a></li></ol></li></ol>
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<h1 class="menu-title">Rust GBA Tutorials</h1>
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<main>
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<a class="header" href="#chapter-0-development-setup" id="chapter-0-development-setup"><h1>Chapter 0: Development Setup</h1></a>
|
||||
<p>Before you can build a GBA game you'll have to follow some special steps to
|
||||
setup the development environment. Perhaps unfortunately, there's enough detail
|
||||
here to warrant a mini-chapter all on its own.</p>
|
||||
<a class="header" href="#per-system-setup" id="per-system-setup"><h2>Per System Setup</h2></a>
|
||||
<p>Obviously you need your computer to have a working rust installation. However,
|
||||
you'll also need to ensure that you're using a nightly toolchain. You can run
|
||||
<code>rustup default nightly</code> to set nightly as the system wide default toolchain, or
|
||||
you can use a <a href="https://github.com/rust-lang-nursery/rustup.rs#the-toolchain-file">toolchain
|
||||
file</a> to use
|
||||
nightly just on a specific project, but either way we'll be assuming nightly
|
||||
from now on.</p>
|
||||
<p>Next you need <a href="https://devkitpro.org/wiki/Getting_Started">devkitpro</a>. They've
|
||||
got a graphical installer for Windows, and <code>pacman</code> support on Linux. We'll be
|
||||
using a few of their binutils for the <code>arm-none-eabi</code> target, and we'll also be
|
||||
using some of their tools that are specific to GBA development, so <em>even if</em> you
|
||||
already have the right binutils for whatever reason, you'll still want devkitpro
|
||||
for the <code>gbafix</code> utility.</p>
|
||||
<ul>
|
||||
<li>On Windows you'll want something like <code>C:\devkitpro\devkitARM\bin</code> and
|
||||
<code>C:\devkitpro\tools\bin</code> to be <a href="https://stackoverflow.com/q/44272416/455232">added to your
|
||||
PATH</a>, depending on where you
|
||||
installed it to and such.</li>
|
||||
<li>On Linux you'll also want it to be added to your path, but if you're using
|
||||
Linux I'll just assume you know how to do all that.</li>
|
||||
</ul>
|
||||
<p>Finally, you'll need <code>cargo-xbuild</code>. Just run <code>cargo install cargo-xbuild</code> and
|
||||
cargo will figure it all out for you.</p>
|
||||
<a class="header" href="#per-project-setup" id="per-project-setup"><h2>Per Project Setup</h2></a>
|
||||
<p>Now you'll need some particular files each time you want to start a new project.
|
||||
You can find them in the root of the <a href="https://github.com/rust-console/gba">rust-console/gba
|
||||
repo</a>.</p>
|
||||
<ul>
|
||||
<li><code>thumbv4-none-agb.json</code> describes the overall GBA to cargo-xbuild so it knows
|
||||
what to do. This is actually a somewhat made up target name since there's no
|
||||
official target name. The GBA is essentially the same as a normal
|
||||
<code>thumbv4-none-eabi</code> device, but we give it the "agb" signifier so that later
|
||||
on we'll be able to use rust's <code>cfg</code> ability to allow our code to know if it's
|
||||
specifically targeting a GBA or some other similar device (like an NDS).</li>
|
||||
<li><code>crt0.s</code> describes some ASM startup stuff. If you have more ASM to place here
|
||||
later on this is where you can put it. You also need to build it into a
|
||||
<code>crt0.o</code> file before it can actually be used, but we'll cover that below.</li>
|
||||
<li><code>linker.ld</code> tells the linker more critical info about the layout expectations
|
||||
that the GBA has about our program.</li>
|
||||
</ul>
|
||||
<a class="header" href="#compiling" id="compiling"><h2>Compiling</h2></a>
|
||||
<p>Once you've got something to build, you perform the following steps:</p>
|
||||
<ul>
|
||||
<li>
|
||||
<p><code>arm-none-eabi-as crt0.s -o crt0.o</code></p>
|
||||
<ul>
|
||||
<li>This builds your text format <code>crt0.s</code> file into object format <code>crt0.o</code>. You
|
||||
don't need to perform it every time, only when <code>crt0.s</code> changes, but you
|
||||
might as well do it every time so that you never forget to because it's a
|
||||
practically instant operation.</li>
|
||||
</ul>
|
||||
</li>
|
||||
<li>
|
||||
<p><code>cargo xbuild --target thumbv4-none-agb.json</code></p>
|
||||
<ul>
|
||||
<li>This builds your Rust source. It accepts <em>most of</em> the normal options, such
|
||||
as <code>--release</code>, and options, such as <code>--bin foo</code> or <code>--examples</code>, that you'd
|
||||
expect <code>cargo</code> to accept.</li>
|
||||
<li>You <strong>can not</strong> build and run tests this way, because they require <code>std</code>,
|
||||
which the GBA doesn't have. You can still run some of your project's tests
|
||||
with <code>cargo test</code>, but that builds for your local machine, so anything
|
||||
specific to the GBA (such as reading and writing registers) won't be
|
||||
testable that way. If you want to isolate and try out some piece code
|
||||
running on the GBA you'll unfortunately have to make a demo for it in your
|
||||
<code>examples/</code> directory and then run the demo in an emulator and see if it
|
||||
does what you expect.</li>
|
||||
<li>The file extension is important. <code>cargo xbuild</code> takes it as a flag to
|
||||
compile dependencies with the same sysroot, so you can include crates
|
||||
normally. Well, creates that work in the GBA's limited environment, but you
|
||||
get the idea.</li>
|
||||
</ul>
|
||||
</li>
|
||||
</ul>
|
||||
<p>At this point you have an ELF binary that some emulators can execute directly.
|
||||
This is helpful because it'll have debug symbols and all that, assuming a debug
|
||||
build. Specifically, <a href="https://mgba.io/2018/09/24/mgba-0.7-beta1/">mgba 0.7 beta
|
||||
1</a> can do it, and perhaps other
|
||||
emulators can also do it.</p>
|
||||
<p>However, if you want a "real" ROM that works in all emulators and that you could
|
||||
transfer to a flash cart there's a little more to do.</p>
|
||||
<ul>
|
||||
<li>
|
||||
<p><code>arm-none-eabi-objcopy -O binary target/thumbv4-none-agb/MODE/BIN_NAME target/ROM_NAME.gba</code></p>
|
||||
<ul>
|
||||
<li>This will perform an <a href="https://linux.die.net/man/1/objcopy">objcopy</a> on our
|
||||
program. Here I've named the program <code>arm-none-eabi-objcopy</code>, which is what
|
||||
devkitpro calls their version of <code>objcopy</code> that's specific to the GBA in the
|
||||
Windows install. If the program isn't found under that name, have a look in
|
||||
your installation directory to see if it's under a slightly different name
|
||||
or something.</li>
|
||||
<li>As you can see from reading the man page, the <code>-O binary</code> option takes our
|
||||
lovely ELF file with symbols and all that and strips it down to basically a
|
||||
bare memory dump of the program.</li>
|
||||
<li>The next argument is the input file. You might not be familiar with how
|
||||
<code>cargo</code> arranges stuff in the <code>target/</code> directory, and between RLS and
|
||||
<code>cargo doc</code> and stuff it gets kinda crowded, so it goes like this:
|
||||
<ul>
|
||||
<li>Since our program was built for a non-local target, first we've got a
|
||||
directory named for that target, <code>thumbv4-none-agb/</code></li>
|
||||
<li>Next, the "MODE" is either <code>debug/</code> or <code>release/</code>, depending on if we had
|
||||
the <code>--release</code> flag included. You'll probably only be packing release
|
||||
mode programs all the way into GBA roms, but it works with either mode.</li>
|
||||
<li>Finally, the name of the program. If your program is something out of the
|
||||
project's <code>src/bin/</code> then it'll be that file's name, or whatever name you
|
||||
configured for the bin in the <code>Cargo.toml</code> file. If your program is
|
||||
something out of the project's <code>examples/</code> directory there will be a
|
||||
similar <code>examples/</code> sub-directory first, and then the example's name.</li>
|
||||
</ul>
|
||||
</li>
|
||||
<li>The final argument is the output of the <code>objcopy</code>, which I suggest putting
|
||||
at just the top level of the <code>target/</code> directory. Really it could go
|
||||
anywhere, but if you're using git then it's likely that your <code>.gitignore</code>
|
||||
file is already setup to exclude everything in <code>target/</code>, so this makes sure
|
||||
that your intermediate game builds don't get checked into your git.</li>
|
||||
</ul>
|
||||
</li>
|
||||
<li>
|
||||
<p><code>gbafix target/ROM_NAME.gba</code></p>
|
||||
<ul>
|
||||
<li>The <code>gbafix</code> tool also comes from devkitpro. The GBA is very picky about a
|
||||
ROM's format, and <code>gbafix</code> patches the ROM's header and such so that it'll
|
||||
work right. Unlike <code>objcopy</code>, this tool is custom built for GBA development,
|
||||
so it works just perfectly without any arguments beyond the file name. The
|
||||
ROM is patched in place, so we don't even need to specify a new destination.</li>
|
||||
</ul>
|
||||
</li>
|
||||
</ul>
|
||||
<p>And you're finally done!</p>
|
||||
<p>Of course, you probably want to make a script for all that, but it's up to you.</p>
|
||||
|
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</main>
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<ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch0/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch1/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch1/hello1.html" class="active"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch1/io_registers.html"><strong aria-hidden="true">3.2.</strong> IO Registers</a></li><li><a href="../ch1/the_display_control_register.html"><strong aria-hidden="true">3.3.</strong> The Display Control Register</a></li><li><a href="../ch1/video_memory_intro.html"><strong aria-hidden="true">3.4.</strong> Video Memory Intro</a></li><li><a href="../ch1/hello2.html"><strong aria-hidden="true">3.5.</strong> hello2</a></li></ol></li></ol>
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<main>
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<a class="header" href="#hello1" id="hello1"><h1>hello1</h1></a>
|
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<p>Ready? Here goes:</p>
|
||||
<p><code>hello1.rs</code></p>
|
||||
<pre><pre class="playpen"><code class="language-rust">#![feature(start)]
|
||||
#![no_std]
|
||||
|
||||
#[cfg(not(test))]
|
||||
#[panic_handler]
|
||||
fn panic(_info: &core::panic::PanicInfo) -> ! {
|
||||
loop {}
|
||||
}
|
||||
|
||||
#[start]
|
||||
fn main(_argc: isize, _argv: *const *const u8) -> isize {
|
||||
unsafe {
|
||||
(0x04000000 as *mut u16).write_volatile(0x0403);
|
||||
(0x06000000 as *mut u16).offset(120 + 80 * 240).write_volatile(0x001F);
|
||||
(0x06000000 as *mut u16).offset(136 + 80 * 240).write_volatile(0x03E0);
|
||||
(0x06000000 as *mut u16).offset(120 + 96 * 240).write_volatile(0x7C00);
|
||||
loop {}
|
||||
}
|
||||
}
|
||||
</code></pre></pre>
|
||||
<p>Throw that into your project, build the program (as described back in Chapter
|
||||
0), and give it a run. You should see a red, green, and blue dot close-ish to
|
||||
the middle of the screen. If you don't, something already went wrong. Double
|
||||
check things, phone a friend, write your senators, try asking Ketsuban on the
|
||||
<a href="https://discordapp.com/invite/aVESxV8">Rust Community Discord</a>, until you're
|
||||
able to get your three dots going.</p>
|
||||
<a class="header" href="#explaining-hello1" id="explaining-hello1"><h2>Explaining hello1</h2></a>
|
||||
<p>So, what just happened? Even if you're used to Rust that might look pretty
|
||||
strange. We'll go over each part extra carefully.</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#![feature(start)]
|
||||
#fn main() {
|
||||
#}</code></pre></pre>
|
||||
<p>This enables the <a href="https://doc.rust-lang.org/beta/unstable-book/language-features/start.html">start
|
||||
feature</a>,
|
||||
which you would normally be able to read about in the unstable book, except that
|
||||
the book tells you nothing at all except to look at the <a href="https://github.com/rust-lang/rust/issues/29633">tracking
|
||||
issue</a>.</p>
|
||||
<p>Basically, a GBA game is even more low-level than the <em>normal</em> amount of
|
||||
low-level that you get from Rust, so we have to tell the compiler to account for
|
||||
that by specifying a <code>#[start]</code>, and we need this feature on to do that.</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#![no_std]
|
||||
#fn main() {
|
||||
#}</code></pre></pre>
|
||||
<p>There's no standard library available on the GBA, so we'll have to live a core
|
||||
only life.</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
#[cfg(not(test))]
|
||||
#[panic_handler]
|
||||
fn panic(_info: &core::panic::PanicInfo) -> ! {
|
||||
loop {}
|
||||
}
|
||||
#}</code></pre></pre>
|
||||
<p>This sets our <a href="https://doc.rust-lang.org/nightly/nomicon/panic-handler.html">panic
|
||||
handler</a>.
|
||||
Basically, if we somehow trigger a panic, this is where the program goes.
|
||||
However, right now we don't know how to get any sort of message out to the user
|
||||
so... we do nothing at all. We <em>can't even return</em> from here, so we just sit in
|
||||
an infinite loop. The player will have to reset the universe from the outside.</p>
|
||||
<p>The <code>#[cfg(not(test))]</code> part makes this item only exist in the program when
|
||||
we're <em>not</em> in a test build. This is so that <code>cargo test</code> and such work right as
|
||||
much as possible.</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">#[start]
|
||||
fn main(_argc: isize, _argv: *const *const u8) -> isize {
|
||||
</code></pre></pre>
|
||||
<p>This is our <code>#[start]</code>. We call it <code>main</code>, but it's not like a <code>main</code> that you'd
|
||||
see in a Rust program. It's <em>more like</em> the sort of <code>main</code> that you'd see in a C
|
||||
program, but it's still <strong>not</strong> that either. If you compile a <code>#[start]</code> program
|
||||
for a target with an OS such as <code>arm-none-eabi-nm</code> you can open up the debug
|
||||
info and see that your result will have the symbol for the C <code>main</code> along side
|
||||
the symbol for the start <code>main</code> that we write here. Our start <code>main</code> is just its
|
||||
own unique thing, and the inputs and outputs have to be like that because that's
|
||||
how <code>#[start]</code> is specified to work in Rust.</p>
|
||||
<p>If you think about it for a moment you'll probably realize that, those inputs
|
||||
and outputs are totally useless to us on a GBA. There's no OS on the GBA to call
|
||||
our program, and there's no place for our program to "return to" when it's done.</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
unsafe {
|
||||
#}</code></pre></pre>
|
||||
<p>I hope you're all set for some <code>unsafe</code>, because there's a lot of it to be had.</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
(0x04000000 as *mut u16).write_volatile(0x0403);
|
||||
#}</code></pre></pre>
|
||||
<p>Sure!</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
(0x06000000 as *mut u16).offset(120 + 80 * 240).write_volatile(0x001F);
|
||||
(0x06000000 as *mut u16).offset(136 + 80 * 240).write_volatile(0x03E0);
|
||||
(0x06000000 as *mut u16).offset(120 + 96 * 240).write_volatile(0x7C00);
|
||||
#}</code></pre></pre>
|
||||
<p>Ah, of course.</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
loop {}
|
||||
}
|
||||
}
|
||||
#}</code></pre></pre>
|
||||
<p>And, as mentioned above, there's no place for a GBA program to "return to", so
|
||||
we can't ever let <code>main</code> try to return there. Instead, we go into an infinite
|
||||
<code>loop</code> that does nothing. The fact that this doesn't ever return an <code>isize</code>
|
||||
value doesn't seem to bother Rust, because I guess we're at least not returning
|
||||
any other type of thing instead.</p>
|
||||
<p>Fun fact: unlike in C++, an infinite loop with no side effects isn't Undefined
|
||||
Behavior for us rustaceans... <em>semantically</em>. In truth LLVM has a <a href="https://github.com/rust-lang/rust/issues/28728">known
|
||||
bug</a> in this area, so we won't
|
||||
actually be relying on empty loops in any future programs.</p>
|
||||
<a class="header" href="#all-those-magic-numbers" id="all-those-magic-numbers"><h2>All Those Magic Numbers</h2></a>
|
||||
<p>Alright, I cheated quite a bit in the middle there. The program works, but I
|
||||
didn't really tell you why because I didn't really tell you what any of those
|
||||
magic numbers mean or do.</p>
|
||||
<ul>
|
||||
<li><code>0x04000000</code> is the address of an IO Register called the Display Control.</li>
|
||||
<li><code>0x06000000</code> is the start of Video RAM.</li>
|
||||
</ul>
|
||||
<p>So we write some magic to the display control register once, then we write some
|
||||
other magic to three locations of magic to the Video RAM. We get three dots,
|
||||
each in their own location... so that second part makes sense at least.</p>
|
||||
<p>We'll get into the magic number details in the other sections of this chapter.</p>
|
||||
<a class="header" href="#sidebar-volatile" id="sidebar-volatile"><h2>Sidebar: Volatile</h2></a>
|
||||
<p>We'll get into what all that is in a moment, but first let's ask ourselves: Why
|
||||
are we doing <em>volatile</em> writes? You've probably never used it before at all.
|
||||
What is volatile anyway?</p>
|
||||
<p>Well, the optimizer is pretty aggressive some of the time, and so it'll skip
|
||||
reads and writes when it thinks can. Like if you write to a pointer once, and
|
||||
then again a moment later, and it didn't see any other reads in between, it'll
|
||||
think that it can just skip doing that first write since it'll get overwritten
|
||||
anyway. Sometimes that's right, but sometimes it's wrong.</p>
|
||||
<p>Marking a read or write as <em>volatile</em> tells the compiler that it really must do
|
||||
that action, and in the exact order that we wrote it out. It says that there
|
||||
might even be special hardware side effects going on that the compiler isn't
|
||||
aware of. In this case, the Display Control write sets a video mode, and the
|
||||
Video RAM writes set pixels that will show up on the screen.</p>
|
||||
<p>Similar to "atomic" operations you might have heard about, all volatile
|
||||
operations are enforced to happen in the exact order that you specify them, but
|
||||
only relative to other volatile operations. So something like</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
c.volatile_write(5);
|
||||
a += b;
|
||||
d.volatile_write(7);
|
||||
#}</code></pre></pre>
|
||||
<p>might end up changing <code>a</code> either before or after the change to <code>c</code>, but the
|
||||
write to <code>d</code> will <em>always</em> happen after the write to <code>c</code>.</p>
|
||||
<p>If you ever use volatile stuff on other platforms it's important to note that
|
||||
volatile doesn't make things thread-safe, you still need atomic for that.
|
||||
However, the GBA doesn't have threads, so we don't have to worry about thread
|
||||
safety concerns.</p>
|
||||
<p>Accordingly, our first bit of code for our library will be a <em>newtype</em> over a
|
||||
normal <code>*mut T</code> so that it has volatile reads and writes as the default. We'll
|
||||
cover the details later on when we try writing a <code>hello2</code> program, once we know
|
||||
more of what's going on.</p>
|
||||
|
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</main>
|
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</html>
|
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293
docs/ch1/hello2.html
Normal file
293
docs/ch1/hello2.html
Normal file
|
|
@ -0,0 +1,293 @@
|
|||
<!DOCTYPE HTML>
|
||||
<html lang="en" class="sidebar-visible no-js">
|
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<head>
|
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<!-- Book generated using mdBook -->
|
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<meta charset="UTF-8">
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<title>hello2 - Rust GBA Tutorials</title>
|
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<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
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<meta name="description" content="">
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<main>
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<a class="header" href="#hello2" id="hello2"><h1>hello2</h1></a>
|
||||
<p>Okay so let's have a look again:</p>
|
||||
<p><code>hello1</code></p>
|
||||
<pre><pre class="playpen"><code class="language-rust">#![feature(start)]
|
||||
#![no_std]
|
||||
|
||||
#[cfg(not(test))]
|
||||
#[panic_handler]
|
||||
fn panic(_info: &core::panic::PanicInfo) -> ! {
|
||||
loop {}
|
||||
}
|
||||
|
||||
#[start]
|
||||
fn main(_argc: isize, _argv: *const *const u8) -> isize {
|
||||
unsafe {
|
||||
(0x04000000 as *mut u16).write_volatile(0x0403);
|
||||
(0x06000000 as *mut u16).offset(120 + 80 * 240).write_volatile(0x001F);
|
||||
(0x06000000 as *mut u16).offset(136 + 80 * 240).write_volatile(0x03E0);
|
||||
(0x06000000 as *mut u16).offset(120 + 96 * 240).write_volatile(0x7C00);
|
||||
loop {}
|
||||
}
|
||||
}
|
||||
</code></pre></pre>
|
||||
<p>Now let's clean this up so that it's clearer what's going on.</p>
|
||||
<p>First we'll label that display control stuff:</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
pub const DISPCNT: *mut u16 = 0x04000000 as *mut u16;
|
||||
pub const MODE3: u16 = 3;
|
||||
pub const BG2: u16 = 0b100_0000_0000;
|
||||
#}</code></pre></pre>
|
||||
<p>Next we make some const values for the actual pixel drawing</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
pub const VRAM: usize = 0x06000000;
|
||||
pub const SCREEN_WIDTH: isize = 240;
|
||||
#}</code></pre></pre>
|
||||
<p>And then we want a small helper function for putting together a color value.</p>
|
||||
<p>Happily, this one can even be declared as a const function. At the time of
|
||||
writing, we've got the "minimal const fn" support in nightly. It really is quite
|
||||
limited, but I'm happy to let rustc and LLVM pre-compute as much as they can
|
||||
when it comes to the GBA's tiny CPU.</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
pub const fn rgb16(red: u16, green: u16, blue: u16) -> u16 {
|
||||
blue << 10 | green << 5 | red
|
||||
}
|
||||
#}</code></pre></pre>
|
||||
<p>Finally, we'll make a function for drawing a pixel in Mode 3. Even though it's
|
||||
just a one-liner, having the "important parts" be labeled as function arguments
|
||||
usually helps you think about it a lot better.</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
pub unsafe fn mode3_pixel(col: isize, row: isize, color: u16) {
|
||||
(VRAM as *mut u16).offset(col + row * SCREEN_WIDTH).write_volatile(color);
|
||||
}
|
||||
#}</code></pre></pre>
|
||||
<p>So now we've got this:</p>
|
||||
<p><code>hello2</code></p>
|
||||
<pre><pre class="playpen"><code class="language-rust">#![feature(start)]
|
||||
#![no_std]
|
||||
|
||||
#[cfg(not(test))]
|
||||
#[panic_handler]
|
||||
fn panic(_info: &core::panic::PanicInfo) -> ! {
|
||||
loop {}
|
||||
}
|
||||
|
||||
#[start]
|
||||
fn main(_argc: isize, _argv: *const *const u8) -> isize {
|
||||
unsafe {
|
||||
DISPCNT.write_volatile(MODE3 | BG2);
|
||||
mode3_pixel(120, 80, rgb16(31, 0, 0));
|
||||
mode3_pixel(136, 80, rgb16(0, 31, 0));
|
||||
mode3_pixel(120, 96, rgb16(0, 0, 31));
|
||||
loop {}
|
||||
}
|
||||
}
|
||||
|
||||
pub const DISPCNT: *mut u16 = 0x04000000 as *mut u16;
|
||||
pub const MODE3: u16 = 3;
|
||||
pub const BG2: u16 = 0b100_0000_0000;
|
||||
|
||||
pub const VRAM: usize = 0x06000000;
|
||||
pub const SCREEN_WIDTH: isize = 240;
|
||||
|
||||
pub const fn rgb16(red: u16, green: u16, blue: u16) -> u16 {
|
||||
blue << 10 | green << 5 | red
|
||||
}
|
||||
|
||||
pub unsafe fn mode3_pixel(col: isize, row: isize, color: u16) {
|
||||
(VRAM as *mut u16).offset(col + row * SCREEN_WIDTH).write_volatile(color);
|
||||
}
|
||||
</code></pre></pre>
|
||||
<p>Exact same program that we started with, but much easier to read.</p>
|
||||
<p>Of course, in the full <code>gba</code> crate that this book is a part of we have these and
|
||||
other elements all labeled and sorted out for you. Still, for educational
|
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purposes it's often best to do it yourself at least once.</p>
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207
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<ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch0/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch1/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch1/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch1/io_registers.html" class="active"><strong aria-hidden="true">3.2.</strong> IO Registers</a></li><li><a href="../ch1/the_display_control_register.html"><strong aria-hidden="true">3.3.</strong> The Display Control Register</a></li><li><a href="../ch1/video_memory_intro.html"><strong aria-hidden="true">3.4.</strong> Video Memory Intro</a></li><li><a href="../ch1/hello2.html"><strong aria-hidden="true">3.5.</strong> hello2</a></li></ol></li></ol>
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<a class="header" href="#io-registers" id="io-registers"><h1>IO Registers</h1></a>
|
||||
<p>The GBA has a large number of <strong>IO Registers</strong> (not to be confused with CPU
|
||||
registers). These are special memory locations from <code>0x04000000</code> to
|
||||
<code>0x040003FE</code>. GBATEK has a <a href="http://problemkaputt.de/gbatek.htm#gbaiomap">full
|
||||
list</a>, but we only need to learn
|
||||
about a few of them at a time as we go, so don't be worried.</p>
|
||||
<p>The important facts to know about IO Registers are these:</p>
|
||||
<ul>
|
||||
<li>Each has their own specific size. Most are <code>u16</code>, but some are <code>u32</code>.</li>
|
||||
<li>All of them must be accessed in a <code>volatile</code> style.</li>
|
||||
<li>Each register is specifically readable or writable or both. Actually, with
|
||||
some registers there are even individual bits that are read-only or
|
||||
write-only.
|
||||
<ul>
|
||||
<li>If you write to a read-only position, those writes are simply ignored. This
|
||||
mostly matters if a writable register contains a read-only bit (such as the
|
||||
Display Control, next section).</li>
|
||||
<li>If you read from a write-only position, you get back values that are
|
||||
<a href="http://problemkaputt.de/gbatek.htm#gbaunpredictablethings">basically
|
||||
nonsense</a>. There
|
||||
aren't really any registers that mix writable bits with read only bits, so
|
||||
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|
||||
value into a write-only register you need to keep track of what you wrote
|
||||
somewhere else if you want to know what you wrote (such to adjust an offset
|
||||
value by +1, or whatever).</li>
|
||||
<li>You can always check GBATEK to be sure, but if I don't mention it then a bit
|
||||
is probably both read and write.</li>
|
||||
</ul>
|
||||
</li>
|
||||
<li>Some registers have invalid bit patterns. For example, the lowest three bits
|
||||
of the Display Control register can't legally be set to the values 6 or 7.</li>
|
||||
</ul>
|
||||
<p>When talking about bit positions, the numbers are <em>zero indexed</em> just like an
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<ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch0/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch1/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch1/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch1/io_registers.html"><strong aria-hidden="true">3.2.</strong> IO Registers</a></li><li><a href="../ch1/the_display_control_register.html" class="active"><strong aria-hidden="true">3.3.</strong> The Display Control Register</a></li><li><a href="../ch1/video_memory_intro.html"><strong aria-hidden="true">3.4.</strong> Video Memory Intro</a></li><li><a href="../ch1/hello2.html"><strong aria-hidden="true">3.5.</strong> hello2</a></li></ol></li></ol>
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<main>
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<a class="header" href="#the-display-control-register" id="the-display-control-register"><h1>The Display Control Register</h1></a>
|
||||
<p>The display control register is our first actual IO Register. GBATEK gives it the
|
||||
shorthand <a href="http://problemkaputt.de/gbatek.htm#lcdiodisplaycontrol">DISPCNT</a>, so
|
||||
you might see it under that name if you read other guides.</p>
|
||||
<p>Among IO Registers, it's one of the simpler ones, but it's got enough complexity
|
||||
that we can get a hint of what's to come.</p>
|
||||
<p>Also it's the one that you basically always need to set at least once in every
|
||||
GBA game, so it's a good starting one to go over for that reason too.</p>
|
||||
<p>The display control register holds a <code>u16</code> value, and is located at <code>0x0400_0000</code>.</p>
|
||||
<p>Many of the bits here won't mean much to you right now. <strong>That is fine.</strong> You do
|
||||
NOT need to memorize them all or what they all do right away. We'll just skim
|
||||
over all the parts of this register to start, and then we'll go into more detail
|
||||
in later chapters when we need to come back and use more of the bits.</p>
|
||||
<a class="header" href="#video-modes" id="video-modes"><h2>Video Modes</h2></a>
|
||||
<p>The lowest three bits (0-2) let you select from among the GBA's six video modes.
|
||||
You'll notice that 3 bits allows for eight modes, but the values 6 and 7 are
|
||||
prohibited.</p>
|
||||
<p>Modes 0, 1, and 2 are "tiled" modes. These are actually the modes that you
|
||||
should eventually learn to use as much as possible. It lets the GBA's limited
|
||||
video hardware do as much of the work as possible, leaving more of your CPU time
|
||||
for gameplay computations. However, they're also complex enough to deserve their
|
||||
own demos and chapters later on, so that's all we'll say about them for now.</p>
|
||||
<p>Modes 3, 4, and 5 are "bitmap" modes. These let you write individual pixels to
|
||||
locations on the screen.</p>
|
||||
<ul>
|
||||
<li><strong>Mode 3</strong> is full resolution (240w x 160h) RGB15 color. You might not be used
|
||||
to RGB15, since modern computers have 24 or 32 bit colors. In RGB15, there's 5
|
||||
bits for each color channel stored within a <code>u16</code> value, and the highest bit is
|
||||
simply ignored.</li>
|
||||
<li><strong>Mode 4</strong> is full resolution paletted color. Instead of being a <code>u16</code> color, each
|
||||
pixel value is a <code>u8</code> palette index entry, and then the display uses the
|
||||
palette memory (which we'll talk about later) to store the actual color data.
|
||||
Since each pixel is half sized, we can fit twice as many. This lets us have
|
||||
two "pages". At any given moment only one page is active, and you can draw to
|
||||
the other page without the user noticing. You set which page to show with
|
||||
another bit we'll get to in a moment.</li>
|
||||
<li><strong>Mode 5</strong> is full color, but also with pages. This means that we must have a
|
||||
reduced resolution to compensate (video memory is only so big!). The screen is
|
||||
effectively only 160w x 128h in this mode.</li>
|
||||
</ul>
|
||||
<a class="header" href="#cgb-mode" id="cgb-mode"><h2>CGB Mode</h2></a>
|
||||
<p>Bit 3 is effectively read only. Technically it can be flipped using a BIOS call,
|
||||
but when you write to the display control register normally it won't write to
|
||||
this bit, so we'll call it effectively read only.</p>
|
||||
<p>This bit is on if the CPU is in CGB mode.</p>
|
||||
<a class="header" href="#page-flipping" id="page-flipping"><h2>Page Flipping</h2></a>
|
||||
<p>Bit 4 lets you pick which page to use. This is only relevent in video modes 4 or
|
||||
5, and is just ignored otherwise. It's very easy to remember: when the bit is 0
|
||||
the 0th page is used, and when the bit is 1 the 1st page is used.</p>
|
||||
<p>The second page always starts at <code>0x0600_A000</code>.</p>
|
||||
<a class="header" href="#oam-vram-and-blanking" id="oam-vram-and-blanking"><h2>OAM, VRAM, and Blanking</h2></a>
|
||||
<p>Bit 5 lets you access OAM during HBlank if enabled. This is cool, but it reduces
|
||||
the maximum sprites per scanline, so it's not default.</p>
|
||||
<p>Bit 6 lets you adjust if the GBA should treat Object Character VRAM as being 2d
|
||||
(off) or 1d (on). This particular control can be kinda tricky to wrap your head
|
||||
around, so we'll be sure to have some extra diagrams in the chapter that deals
|
||||
with it.</p>
|
||||
<p>Bit 7 forces the screen to stay in vblank as long as it's set. This allows the
|
||||
fastest use of the VRAM, Palette, and Object Attribute Memory. Obviously if you
|
||||
leave this on for too long the player will notice a blank screen, but it might
|
||||
be okay to use for a moment or two every once in a while.</p>
|
||||
<a class="header" href="#screen-layers" id="screen-layers"><h2>Screen Layers</h2></a>
|
||||
<p>Bits 8 through 11 control if Background layers 0 through 3 should be active.</p>
|
||||
<p>Bit 12 affects the Object layer.</p>
|
||||
<p>Note that not all background layers are available in all video modes:</p>
|
||||
<ul>
|
||||
<li>Mode 0: all</li>
|
||||
<li>Mode 1: 0/1/2</li>
|
||||
<li>Mode 2: 2/3</li>
|
||||
<li>Mode 3/4/5: 2</li>
|
||||
</ul>
|
||||
<p>Bit 13 and 14 enable the display of Windows 0 and 1, and Bit 15 enables the
|
||||
object display window. We'll get into how windows work later on, they let you do
|
||||
some nifty graphical effects.</p>
|
||||
<a class="header" href="#in-conclusion" id="in-conclusion"><h2>In Conclusion...</h2></a>
|
||||
<p>So what did we do to the display control register in <code>hello1</code>?</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
(0x04000000 as *mut u16).write_volatile(0x0403);
|
||||
#}</code></pre></pre>
|
||||
<p>First let's <a href="https://www.wolframalpha.com/input/?i=0x0403">convert that to
|
||||
binary</a>, and we get
|
||||
<code>0b100_0000_0011</code>. So, that's setting Mode 3 with background 2 enabled and
|
||||
nothing else special.</p>
|
||||
<p>However, I think we can do better than that. This is a prime target for more
|
||||
newtyping as we attempt a <code>hello2</code> program.</p>
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<ol class="chapter"><li><a href="../introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="../ch0/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="../ch1/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="../ch1/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="../ch1/io_registers.html"><strong aria-hidden="true">3.2.</strong> IO Registers</a></li><li><a href="../ch1/the_display_control_register.html"><strong aria-hidden="true">3.3.</strong> The Display Control Register</a></li><li><a href="../ch1/video_memory_intro.html" class="active"><strong aria-hidden="true">3.4.</strong> Video Memory Intro</a></li><li><a href="../ch1/hello2.html"><strong aria-hidden="true">3.5.</strong> hello2</a></li></ol></li></ol>
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<a class="header" href="#video-memory-intro" id="video-memory-intro"><h1>Video Memory Intro</h1></a>
|
||||
<p>The GBA's Video RAM is 96k stretching from <code>0x0600_0000</code> to <code>0x0601_7FFF</code>.</p>
|
||||
<p>The Video RAM can only be accessed totally freely during a Vertical Blank
|
||||
(aka "vblank"). At other times, if the CPU tries to touch the same part of video
|
||||
memory as the display controller is accessing then the CPU gets bumped by a
|
||||
cycle to avoid a clash.</p>
|
||||
<p>Annoyingly, VRAM can only be properly written to in 16 and 32 bit segments (same
|
||||
with PALRAM and OAM). If you try to write just an 8 bit segment, then both parts
|
||||
of the 16 bit segment get the same value written to them. In other words, if you
|
||||
write the byte <code>5</code> to <code>0x0600_0000</code>, then both <code>0x0600_0000</code> and ALSO
|
||||
<code>0x0600_0001</code> will have the byte <code>5</code> in them. We have to be extra careful when
|
||||
trying to set an individual byte, and we also have to be careful if we use
|
||||
<code>memcopy</code> or <code>memset</code> as well, because they're byte oriented by default and
|
||||
don't know to follow the special rules.</p>
|
||||
<a class="header" href="#rgb15" id="rgb15"><h2>RGB15</h2></a>
|
||||
<p>As I said before, RGB15 stores a color within a <code>u16</code> value using 5 bits for
|
||||
each color channel.</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
pub const RED: u16 = 0b0_00000_00000_11111;
|
||||
pub const GREEN: u16 = 0b0_00000_11111_00000;
|
||||
pub const BLUE: u16 = 0b0_11111_00000_00000;
|
||||
#}</code></pre></pre>
|
||||
<p>In Mode 3 and Mode 5 we write direct color values into VRAM, and in Mode 4 we
|
||||
write palette index values, and then the color values go into the PALRAM.</p>
|
||||
<a class="header" href="#mode-3" id="mode-3"><h2>Mode 3</h2></a>
|
||||
<p>Mode 3 is pretty easy. We have a full resolution grid of rgb15 pixels. There's
|
||||
160 rows of 240 pixels each, with the base address being the top left corner. A
|
||||
particular pixel uses normal "2d indexing" math:</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
let row_five_col_seven = 5 + (7 * SCREEN_WIDTH);
|
||||
#}</code></pre></pre>
|
||||
<p>To draw a pixel, we just write a value at the address for the row and col that
|
||||
we want to draw to.</p>
|
||||
<a class="header" href="#mode-4" id="mode-4"><h2>Mode 4</h2></a>
|
||||
<p>Mode 4 introduces page flipping. Instead of one giant page at <code>0x0600_0000</code>,
|
||||
there's Page 0 at <code>0x0600_0000</code> and then Page 1 at <code>0x0600_A000</code>. The resolution
|
||||
for each page is the same as above, but instead of writing <code>u16</code> values, the
|
||||
memory is treated as <code>u8</code> indexes into PALRAM. The PALRAM starts at
|
||||
<code>0x0500_0000</code>, and there's enough space for 256 palette entries (each a <code>u16</code>).</p>
|
||||
<p>To set the color of a palette entry we just do a normal <code>u16</code> write_volatile.</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
(0x0500_0000 as *mut u16).offset(target_index).write_volatile(new_color)
|
||||
#}</code></pre></pre>
|
||||
<p>To draw a pixel we set the palette entry that we want the pixel to use. However,
|
||||
we must remember the "minimum size" write limitation that applies to VRAM. So,
|
||||
if we want to change just a single pixel at a time we must</p>
|
||||
<ol>
|
||||
<li>Read the full <code>u16</code> it's a part of.</li>
|
||||
<li>Clear the half of the <code>u16</code> we're going to replace</li>
|
||||
<li>Write the half of the <code>u16</code> we're going to replace with the new value</li>
|
||||
<li>Write that result back to the address.</li>
|
||||
</ol>
|
||||
<p>So, the math for finding a byte offset is the same as Mode 3 (since they're both
|
||||
a 2d grid). If the byte offset is EVEN it'll be the high bits of the <code>u16</code> at
|
||||
half the byte offset rounded down. If the offset is ODD it'll be the low bits of
|
||||
the <code>u16</code> at half the byte.</p>
|
||||
<p>Does that make sense?</p>
|
||||
<ul>
|
||||
<li>If we want to write pixel (0,0) the byte offset is 0, so we change the high
|
||||
bits of <code>u16</code> offset 0. Then we want to write to (1,0), so the byte offset is
|
||||
1, so we change the low bits of <code>u16</code> offset 0. The pixels are next to each
|
||||
other, and the target bytes are next to each other, good so far.</li>
|
||||
<li>If we want to write to (5,6) that'd be byte <code>5 + 6 * 240 = 1445</code>, so we'd
|
||||
target the low bits of <code>u16</code> offset <code>floor(1445/2) = 722</code>.</li>
|
||||
</ul>
|
||||
<p>As you can see, trying to write individual pixels in Mode 4 is mostly a bad
|
||||
time. Fret not! We don't <em>have</em> to write individual bytes. If our data is
|
||||
arranged correctly ahead of time we can just write <code>u16</code> or <code>u32</code> values
|
||||
directly. The video hardware doesn't care, it'll get along just fine.</p>
|
||||
<a class="header" href="#mode-5" id="mode-5"><h2>Mode 5</h2></a>
|
||||
<p>Mode 5 is also a two page mode, but instead of compressing the size of a pixel's
|
||||
data to fit in two pages, we compress the resolution.</p>
|
||||
<p>Mode 5 is full <code>u16</code> color, but only 160w x 128h per page.</p>
|
||||
<a class="header" href="#in-conclusion" id="in-conclusion"><h2>In Conclusion...</h2></a>
|
||||
<p>So what got written into VRAM in <code>hello1</code>?</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
(0x06000000 as *mut u16).offset(120 + 80 * 240).write_volatile(0x001F);
|
||||
(0x06000000 as *mut u16).offset(136 + 80 * 240).write_volatile(0x03E0);
|
||||
(0x06000000 as *mut u16).offset(120 + 96 * 240).write_volatile(0x7C00);
|
||||
#}</code></pre></pre>
|
||||
<p>So at pixels <code>(120,80)</code>, <code>(136,80)</code>, and <code>(120,96)</code> we write three values. Once
|
||||
again we probably need to <a href="https://www.wolframalpha.com/">convert them</a> into
|
||||
binary to make sense of it.</p>
|
||||
<ul>
|
||||
<li>0x001F: 0b11111</li>
|
||||
<li>0x03E0: 0b11111_00000</li>
|
||||
<li>0x7C00: 0b11111_00000_00000</li>
|
||||
</ul>
|
||||
<p>Ah, of course, a red pixel, a green pixel, and a blue pixel.</p>
|
||||
|
||||
</main>
|
||||
|
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<head>
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<meta charset="UTF-8">
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<title>ch01 - Rust GBA Tutorials</title>
|
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<title>Introduction - Rust GBA Tutorials</title>
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<ol class="chapter"><li><a href="ch01.html"><strong aria-hidden="true">1.</strong> ch01</a></li></ol>
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<ol class="chapter"><li><a href="introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="ch0/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="ch1/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="ch1/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="ch1/io_registers.html"><strong aria-hidden="true">3.2.</strong> IO Registers</a></li><li><a href="ch1/the_display_control_register.html"><strong aria-hidden="true">3.3.</strong> The Display Control Register</a></li><li><a href="ch1/video_memory_intro.html"><strong aria-hidden="true">3.4.</strong> Video Memory Intro</a></li><li><a href="ch1/hello2.html"><strong aria-hidden="true">3.5.</strong> hello2</a></li></ol></li></ol>
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<main>
|
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<a class="header" href="#ch01" id="ch01"><h1>ch01</h1></a>
|
||||
<a class="header" href="#introduction" id="introduction"><h1>Introduction</h1></a>
|
||||
<p>Here's a book that'll help you program in Rust on the GBA.</p>
|
||||
<p>It's very "work in progress". At the moment there's only one demo program.</p>
|
||||
<a class="header" href="#other-works" id="other-works"><h2>Other Works</h2></a>
|
||||
<p>If you want to read more about developing on the GBA there are some other good resources as well:</p>
|
||||
<ul>
|
||||
<li><a href="https://www.coranac.com/tonc/text/toc.htm">Tonc</a>, a tutorial series written
|
||||
for C, but it's what I based the ordering of this book's sections on.</li>
|
||||
<li><a href="http://problemkaputt.de/gbatek.htm">GBATEK</a>, a homebrew tech manual for
|
||||
GBA/NDS/DSi. We will regularly link to parts of it when talking about various
|
||||
bits of the GBA.</li>
|
||||
</ul>
|
||||
|
||||
</main>
|
||||
|
||||
|
|
|
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@ -3,7 +3,7 @@
|
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<head>
|
||||
<!-- Book generated using mdBook -->
|
||||
<meta charset="UTF-8">
|
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<title>ch01 - Rust GBA Tutorials</title>
|
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<title>Introduction - Rust GBA Tutorials</title>
|
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<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
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<ol class="chapter"><li><a href="ch01.html" class="active"><strong aria-hidden="true">1.</strong> ch01</a></li></ol>
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<ol class="chapter"><li><a href="introduction.html" class="active"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="ch0/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="ch1/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="ch1/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="ch1/io_registers.html"><strong aria-hidden="true">3.2.</strong> IO Registers</a></li><li><a href="ch1/the_display_control_register.html"><strong aria-hidden="true">3.3.</strong> The Display Control Register</a></li><li><a href="ch1/video_memory_intro.html"><strong aria-hidden="true">3.4.</strong> Video Memory Intro</a></li><li><a href="ch1/hello2.html"><strong aria-hidden="true">3.5.</strong> hello2</a></li></ol></li></ol>
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<main>
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<a class="header" href="#ch01" id="ch01"><h1>ch01</h1></a>
|
||||
<a class="header" href="#introduction" id="introduction"><h1>Introduction</h1></a>
|
||||
<p>Here's a book that'll help you program in Rust on the GBA.</p>
|
||||
<p>It's very "work in progress". At the moment there's only one demo program.</p>
|
||||
<a class="header" href="#other-works" id="other-works"><h2>Other Works</h2></a>
|
||||
<p>If you want to read more about developing on the GBA there are some other good resources as well:</p>
|
||||
<ul>
|
||||
<li><a href="https://www.coranac.com/tonc/text/toc.htm">Tonc</a>, a tutorial series written
|
||||
for C, but it's what I based the ordering of this book's sections on.</li>
|
||||
<li><a href="http://problemkaputt.de/gbatek.htm">GBATEK</a>, a homebrew tech manual for
|
||||
GBA/NDS/DSi. We will regularly link to parts of it when talking about various
|
||||
bits of the GBA.</li>
|
||||
</ul>
|
||||
|
||||
</main>
|
||||
|
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|
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@ -145,6 +156,10 @@
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643
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<ol class="chapter"><li><a href="introduction.html"><strong aria-hidden="true">1.</strong> Introduction</a></li><li><a href="ch0/index.html"><strong aria-hidden="true">2.</strong> Ch 0: Development Setup</a></li><li><a href="ch1/index.html"><strong aria-hidden="true">3.</strong> Ch 1: Hello GBA</a></li><li><ol class="section"><li><a href="ch1/hello1.html"><strong aria-hidden="true">3.1.</strong> hello1</a></li><li><a href="ch1/io_registers.html"><strong aria-hidden="true">3.2.</strong> IO Registers</a></li><li><a href="ch1/the_display_control_register.html"><strong aria-hidden="true">3.3.</strong> The Display Control Register</a></li><li><a href="ch1/video_memory_intro.html"><strong aria-hidden="true">3.4.</strong> Video Memory Intro</a></li><li><a href="ch1/hello2.html"><strong aria-hidden="true">3.5.</strong> hello2</a></li></ol></li></ol>
|
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</nav>
|
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|
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<div id="page-wrapper" class="page-wrapper">
|
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|
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@ -136,7 +136,646 @@
|
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|
||||
<div id="content" class="content">
|
||||
<main>
|
||||
<a class="header" href="#ch01" id="ch01"><h1>ch01</h1></a>
|
||||
<a class="header" href="#introduction" id="introduction"><h1>Introduction</h1></a>
|
||||
<p>Here's a book that'll help you program in Rust on the GBA.</p>
|
||||
<p>It's very "work in progress". At the moment there's only one demo program.</p>
|
||||
<a class="header" href="#other-works" id="other-works"><h2>Other Works</h2></a>
|
||||
<p>If you want to read more about developing on the GBA there are some other good resources as well:</p>
|
||||
<ul>
|
||||
<li><a href="https://www.coranac.com/tonc/text/toc.htm">Tonc</a>, a tutorial series written
|
||||
for C, but it's what I based the ordering of this book's sections on.</li>
|
||||
<li><a href="http://problemkaputt.de/gbatek.htm">GBATEK</a>, a homebrew tech manual for
|
||||
GBA/NDS/DSi. We will regularly link to parts of it when talking about various
|
||||
bits of the GBA.</li>
|
||||
</ul>
|
||||
<a class="header" href="#chapter-0-development-setup" id="chapter-0-development-setup"><h1>Chapter 0: Development Setup</h1></a>
|
||||
<p>Before you can build a GBA game you'll have to follow some special steps to
|
||||
setup the development environment. Perhaps unfortunately, there's enough detail
|
||||
here to warrant a mini-chapter all on its own.</p>
|
||||
<a class="header" href="#per-system-setup" id="per-system-setup"><h2>Per System Setup</h2></a>
|
||||
<p>Obviously you need your computer to have a working rust installation. However,
|
||||
you'll also need to ensure that you're using a nightly toolchain. You can run
|
||||
<code>rustup default nightly</code> to set nightly as the system wide default toolchain, or
|
||||
you can use a <a href="https://github.com/rust-lang-nursery/rustup.rs#the-toolchain-file">toolchain
|
||||
file</a> to use
|
||||
nightly just on a specific project, but either way we'll be assuming nightly
|
||||
from now on.</p>
|
||||
<p>Next you need <a href="https://devkitpro.org/wiki/Getting_Started">devkitpro</a>. They've
|
||||
got a graphical installer for Windows, and <code>pacman</code> support on Linux. We'll be
|
||||
using a few of their binutils for the <code>arm-none-eabi</code> target, and we'll also be
|
||||
using some of their tools that are specific to GBA development, so <em>even if</em> you
|
||||
already have the right binutils for whatever reason, you'll still want devkitpro
|
||||
for the <code>gbafix</code> utility.</p>
|
||||
<ul>
|
||||
<li>On Windows you'll want something like <code>C:\devkitpro\devkitARM\bin</code> and
|
||||
<code>C:\devkitpro\tools\bin</code> to be <a href="https://stackoverflow.com/q/44272416/455232">added to your
|
||||
PATH</a>, depending on where you
|
||||
installed it to and such.</li>
|
||||
<li>On Linux you'll also want it to be added to your path, but if you're using
|
||||
Linux I'll just assume you know how to do all that.</li>
|
||||
</ul>
|
||||
<p>Finally, you'll need <code>cargo-xbuild</code>. Just run <code>cargo install cargo-xbuild</code> and
|
||||
cargo will figure it all out for you.</p>
|
||||
<a class="header" href="#per-project-setup" id="per-project-setup"><h2>Per Project Setup</h2></a>
|
||||
<p>Now you'll need some particular files each time you want to start a new project.
|
||||
You can find them in the root of the <a href="https://github.com/rust-console/gba">rust-console/gba
|
||||
repo</a>.</p>
|
||||
<ul>
|
||||
<li><code>thumbv4-none-agb.json</code> describes the overall GBA to cargo-xbuild so it knows
|
||||
what to do. This is actually a somewhat made up target name since there's no
|
||||
official target name. The GBA is essentially the same as a normal
|
||||
<code>thumbv4-none-eabi</code> device, but we give it the "agb" signifier so that later
|
||||
on we'll be able to use rust's <code>cfg</code> ability to allow our code to know if it's
|
||||
specifically targeting a GBA or some other similar device (like an NDS).</li>
|
||||
<li><code>crt0.s</code> describes some ASM startup stuff. If you have more ASM to place here
|
||||
later on this is where you can put it. You also need to build it into a
|
||||
<code>crt0.o</code> file before it can actually be used, but we'll cover that below.</li>
|
||||
<li><code>linker.ld</code> tells the linker more critical info about the layout expectations
|
||||
that the GBA has about our program.</li>
|
||||
</ul>
|
||||
<a class="header" href="#compiling" id="compiling"><h2>Compiling</h2></a>
|
||||
<p>Once you've got something to build, you perform the following steps:</p>
|
||||
<ul>
|
||||
<li>
|
||||
<p><code>arm-none-eabi-as crt0.s -o crt0.o</code></p>
|
||||
<ul>
|
||||
<li>This builds your text format <code>crt0.s</code> file into object format <code>crt0.o</code>. You
|
||||
don't need to perform it every time, only when <code>crt0.s</code> changes, but you
|
||||
might as well do it every time so that you never forget to because it's a
|
||||
practically instant operation.</li>
|
||||
</ul>
|
||||
</li>
|
||||
<li>
|
||||
<p><code>cargo xbuild --target thumbv4-none-agb.json</code></p>
|
||||
<ul>
|
||||
<li>This builds your Rust source. It accepts <em>most of</em> the normal options, such
|
||||
as <code>--release</code>, and options, such as <code>--bin foo</code> or <code>--examples</code>, that you'd
|
||||
expect <code>cargo</code> to accept.</li>
|
||||
<li>You <strong>can not</strong> build and run tests this way, because they require <code>std</code>,
|
||||
which the GBA doesn't have. You can still run some of your project's tests
|
||||
with <code>cargo test</code>, but that builds for your local machine, so anything
|
||||
specific to the GBA (such as reading and writing registers) won't be
|
||||
testable that way. If you want to isolate and try out some piece code
|
||||
running on the GBA you'll unfortunately have to make a demo for it in your
|
||||
<code>examples/</code> directory and then run the demo in an emulator and see if it
|
||||
does what you expect.</li>
|
||||
<li>The file extension is important. <code>cargo xbuild</code> takes it as a flag to
|
||||
compile dependencies with the same sysroot, so you can include crates
|
||||
normally. Well, creates that work in the GBA's limited environment, but you
|
||||
get the idea.</li>
|
||||
</ul>
|
||||
</li>
|
||||
</ul>
|
||||
<p>At this point you have an ELF binary that some emulators can execute directly.
|
||||
This is helpful because it'll have debug symbols and all that, assuming a debug
|
||||
build. Specifically, <a href="https://mgba.io/2018/09/24/mgba-0.7-beta1/">mgba 0.7 beta
|
||||
1</a> can do it, and perhaps other
|
||||
emulators can also do it.</p>
|
||||
<p>However, if you want a "real" ROM that works in all emulators and that you could
|
||||
transfer to a flash cart there's a little more to do.</p>
|
||||
<ul>
|
||||
<li>
|
||||
<p><code>arm-none-eabi-objcopy -O binary target/thumbv4-none-agb/MODE/BIN_NAME target/ROM_NAME.gba</code></p>
|
||||
<ul>
|
||||
<li>This will perform an <a href="https://linux.die.net/man/1/objcopy">objcopy</a> on our
|
||||
program. Here I've named the program <code>arm-none-eabi-objcopy</code>, which is what
|
||||
devkitpro calls their version of <code>objcopy</code> that's specific to the GBA in the
|
||||
Windows install. If the program isn't found under that name, have a look in
|
||||
your installation directory to see if it's under a slightly different name
|
||||
or something.</li>
|
||||
<li>As you can see from reading the man page, the <code>-O binary</code> option takes our
|
||||
lovely ELF file with symbols and all that and strips it down to basically a
|
||||
bare memory dump of the program.</li>
|
||||
<li>The next argument is the input file. You might not be familiar with how
|
||||
<code>cargo</code> arranges stuff in the <code>target/</code> directory, and between RLS and
|
||||
<code>cargo doc</code> and stuff it gets kinda crowded, so it goes like this:
|
||||
<ul>
|
||||
<li>Since our program was built for a non-local target, first we've got a
|
||||
directory named for that target, <code>thumbv4-none-agb/</code></li>
|
||||
<li>Next, the "MODE" is either <code>debug/</code> or <code>release/</code>, depending on if we had
|
||||
the <code>--release</code> flag included. You'll probably only be packing release
|
||||
mode programs all the way into GBA roms, but it works with either mode.</li>
|
||||
<li>Finally, the name of the program. If your program is something out of the
|
||||
project's <code>src/bin/</code> then it'll be that file's name, or whatever name you
|
||||
configured for the bin in the <code>Cargo.toml</code> file. If your program is
|
||||
something out of the project's <code>examples/</code> directory there will be a
|
||||
similar <code>examples/</code> sub-directory first, and then the example's name.</li>
|
||||
</ul>
|
||||
</li>
|
||||
<li>The final argument is the output of the <code>objcopy</code>, which I suggest putting
|
||||
at just the top level of the <code>target/</code> directory. Really it could go
|
||||
anywhere, but if you're using git then it's likely that your <code>.gitignore</code>
|
||||
file is already setup to exclude everything in <code>target/</code>, so this makes sure
|
||||
that your intermediate game builds don't get checked into your git.</li>
|
||||
</ul>
|
||||
</li>
|
||||
<li>
|
||||
<p><code>gbafix target/ROM_NAME.gba</code></p>
|
||||
<ul>
|
||||
<li>The <code>gbafix</code> tool also comes from devkitpro. The GBA is very picky about a
|
||||
ROM's format, and <code>gbafix</code> patches the ROM's header and such so that it'll
|
||||
work right. Unlike <code>objcopy</code>, this tool is custom built for GBA development,
|
||||
so it works just perfectly without any arguments beyond the file name. The
|
||||
ROM is patched in place, so we don't even need to specify a new destination.</li>
|
||||
</ul>
|
||||
</li>
|
||||
</ul>
|
||||
<p>And you're finally done!</p>
|
||||
<p>Of course, you probably want to make a script for all that, but it's up to you.</p>
|
||||
<a class="header" href="#ch-1-hello-gba" id="ch-1-hello-gba"><h1>Ch 1: Hello GBA</h1></a>
|
||||
<p>Traditionally a person writes a "hello, world" program so that they can test
|
||||
that their development environment is setup properly and to just get a feel for
|
||||
using the tools involved. To get an idea of what a small part of a source file
|
||||
will look like. All that stuff.</p>
|
||||
<p>Normally, you write a program that prints "hello, world" to the terminal. The
|
||||
GBA has no terminal, but it does have a screen, so instead we're going to draw
|
||||
three dots to the screen.</p>
|
||||
<a class="header" href="#hello1" id="hello1"><h1>hello1</h1></a>
|
||||
<p>Ready? Here goes:</p>
|
||||
<p><code>hello1.rs</code></p>
|
||||
<pre><pre class="playpen"><code class="language-rust">#![feature(start)]
|
||||
#![no_std]
|
||||
|
||||
#[cfg(not(test))]
|
||||
#[panic_handler]
|
||||
fn panic(_info: &core::panic::PanicInfo) -> ! {
|
||||
loop {}
|
||||
}
|
||||
|
||||
#[start]
|
||||
fn main(_argc: isize, _argv: *const *const u8) -> isize {
|
||||
unsafe {
|
||||
(0x04000000 as *mut u16).write_volatile(0x0403);
|
||||
(0x06000000 as *mut u16).offset(120 + 80 * 240).write_volatile(0x001F);
|
||||
(0x06000000 as *mut u16).offset(136 + 80 * 240).write_volatile(0x03E0);
|
||||
(0x06000000 as *mut u16).offset(120 + 96 * 240).write_volatile(0x7C00);
|
||||
loop {}
|
||||
}
|
||||
}
|
||||
</code></pre></pre>
|
||||
<p>Throw that into your project, build the program (as described back in Chapter
|
||||
0), and give it a run. You should see a red, green, and blue dot close-ish to
|
||||
the middle of the screen. If you don't, something already went wrong. Double
|
||||
check things, phone a friend, write your senators, try asking Ketsuban on the
|
||||
<a href="https://discordapp.com/invite/aVESxV8">Rust Community Discord</a>, until you're
|
||||
able to get your three dots going.</p>
|
||||
<a class="header" href="#explaining-hello1" id="explaining-hello1"><h2>Explaining hello1</h2></a>
|
||||
<p>So, what just happened? Even if you're used to Rust that might look pretty
|
||||
strange. We'll go over each part extra carefully.</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#![feature(start)]
|
||||
#fn main() {
|
||||
#}</code></pre></pre>
|
||||
<p>This enables the <a href="https://doc.rust-lang.org/beta/unstable-book/language-features/start.html">start
|
||||
feature</a>,
|
||||
which you would normally be able to read about in the unstable book, except that
|
||||
the book tells you nothing at all except to look at the <a href="https://github.com/rust-lang/rust/issues/29633">tracking
|
||||
issue</a>.</p>
|
||||
<p>Basically, a GBA game is even more low-level than the <em>normal</em> amount of
|
||||
low-level that you get from Rust, so we have to tell the compiler to account for
|
||||
that by specifying a <code>#[start]</code>, and we need this feature on to do that.</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#![no_std]
|
||||
#fn main() {
|
||||
#}</code></pre></pre>
|
||||
<p>There's no standard library available on the GBA, so we'll have to live a core
|
||||
only life.</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
#[cfg(not(test))]
|
||||
#[panic_handler]
|
||||
fn panic(_info: &core::panic::PanicInfo) -> ! {
|
||||
loop {}
|
||||
}
|
||||
#}</code></pre></pre>
|
||||
<p>This sets our <a href="https://doc.rust-lang.org/nightly/nomicon/panic-handler.html">panic
|
||||
handler</a>.
|
||||
Basically, if we somehow trigger a panic, this is where the program goes.
|
||||
However, right now we don't know how to get any sort of message out to the user
|
||||
so... we do nothing at all. We <em>can't even return</em> from here, so we just sit in
|
||||
an infinite loop. The player will have to reset the universe from the outside.</p>
|
||||
<p>The <code>#[cfg(not(test))]</code> part makes this item only exist in the program when
|
||||
we're <em>not</em> in a test build. This is so that <code>cargo test</code> and such work right as
|
||||
much as possible.</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">#[start]
|
||||
fn main(_argc: isize, _argv: *const *const u8) -> isize {
|
||||
</code></pre></pre>
|
||||
<p>This is our <code>#[start]</code>. We call it <code>main</code>, but it's not like a <code>main</code> that you'd
|
||||
see in a Rust program. It's <em>more like</em> the sort of <code>main</code> that you'd see in a C
|
||||
program, but it's still <strong>not</strong> that either. If you compile a <code>#[start]</code> program
|
||||
for a target with an OS such as <code>arm-none-eabi-nm</code> you can open up the debug
|
||||
info and see that your result will have the symbol for the C <code>main</code> along side
|
||||
the symbol for the start <code>main</code> that we write here. Our start <code>main</code> is just its
|
||||
own unique thing, and the inputs and outputs have to be like that because that's
|
||||
how <code>#[start]</code> is specified to work in Rust.</p>
|
||||
<p>If you think about it for a moment you'll probably realize that, those inputs
|
||||
and outputs are totally useless to us on a GBA. There's no OS on the GBA to call
|
||||
our program, and there's no place for our program to "return to" when it's done.</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
unsafe {
|
||||
#}</code></pre></pre>
|
||||
<p>I hope you're all set for some <code>unsafe</code>, because there's a lot of it to be had.</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
(0x04000000 as *mut u16).write_volatile(0x0403);
|
||||
#}</code></pre></pre>
|
||||
<p>Sure!</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
(0x06000000 as *mut u16).offset(120 + 80 * 240).write_volatile(0x001F);
|
||||
(0x06000000 as *mut u16).offset(136 + 80 * 240).write_volatile(0x03E0);
|
||||
(0x06000000 as *mut u16).offset(120 + 96 * 240).write_volatile(0x7C00);
|
||||
#}</code></pre></pre>
|
||||
<p>Ah, of course.</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
loop {}
|
||||
}
|
||||
}
|
||||
#}</code></pre></pre>
|
||||
<p>And, as mentioned above, there's no place for a GBA program to "return to", so
|
||||
we can't ever let <code>main</code> try to return there. Instead, we go into an infinite
|
||||
<code>loop</code> that does nothing. The fact that this doesn't ever return an <code>isize</code>
|
||||
value doesn't seem to bother Rust, because I guess we're at least not returning
|
||||
any other type of thing instead.</p>
|
||||
<p>Fun fact: unlike in C++, an infinite loop with no side effects isn't Undefined
|
||||
Behavior for us rustaceans... <em>semantically</em>. In truth LLVM has a <a href="https://github.com/rust-lang/rust/issues/28728">known
|
||||
bug</a> in this area, so we won't
|
||||
actually be relying on empty loops in any future programs.</p>
|
||||
<a class="header" href="#all-those-magic-numbers" id="all-those-magic-numbers"><h2>All Those Magic Numbers</h2></a>
|
||||
<p>Alright, I cheated quite a bit in the middle there. The program works, but I
|
||||
didn't really tell you why because I didn't really tell you what any of those
|
||||
magic numbers mean or do.</p>
|
||||
<ul>
|
||||
<li><code>0x04000000</code> is the address of an IO Register called the Display Control.</li>
|
||||
<li><code>0x06000000</code> is the start of Video RAM.</li>
|
||||
</ul>
|
||||
<p>So we write some magic to the display control register once, then we write some
|
||||
other magic to three locations of magic to the Video RAM. We get three dots,
|
||||
each in their own location... so that second part makes sense at least.</p>
|
||||
<p>We'll get into the magic number details in the other sections of this chapter.</p>
|
||||
<a class="header" href="#sidebar-volatile" id="sidebar-volatile"><h2>Sidebar: Volatile</h2></a>
|
||||
<p>We'll get into what all that is in a moment, but first let's ask ourselves: Why
|
||||
are we doing <em>volatile</em> writes? You've probably never used it before at all.
|
||||
What is volatile anyway?</p>
|
||||
<p>Well, the optimizer is pretty aggressive some of the time, and so it'll skip
|
||||
reads and writes when it thinks can. Like if you write to a pointer once, and
|
||||
then again a moment later, and it didn't see any other reads in between, it'll
|
||||
think that it can just skip doing that first write since it'll get overwritten
|
||||
anyway. Sometimes that's right, but sometimes it's wrong.</p>
|
||||
<p>Marking a read or write as <em>volatile</em> tells the compiler that it really must do
|
||||
that action, and in the exact order that we wrote it out. It says that there
|
||||
might even be special hardware side effects going on that the compiler isn't
|
||||
aware of. In this case, the Display Control write sets a video mode, and the
|
||||
Video RAM writes set pixels that will show up on the screen.</p>
|
||||
<p>Similar to "atomic" operations you might have heard about, all volatile
|
||||
operations are enforced to happen in the exact order that you specify them, but
|
||||
only relative to other volatile operations. So something like</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
c.volatile_write(5);
|
||||
a += b;
|
||||
d.volatile_write(7);
|
||||
#}</code></pre></pre>
|
||||
<p>might end up changing <code>a</code> either before or after the change to <code>c</code>, but the
|
||||
write to <code>d</code> will <em>always</em> happen after the write to <code>c</code>.</p>
|
||||
<p>If you ever use volatile stuff on other platforms it's important to note that
|
||||
volatile doesn't make things thread-safe, you still need atomic for that.
|
||||
However, the GBA doesn't have threads, so we don't have to worry about thread
|
||||
safety concerns.</p>
|
||||
<p>Accordingly, our first bit of code for our library will be a <em>newtype</em> over a
|
||||
normal <code>*mut T</code> so that it has volatile reads and writes as the default. We'll
|
||||
cover the details later on when we try writing a <code>hello2</code> program, once we know
|
||||
more of what's going on.</p>
|
||||
<a class="header" href="#io-registers" id="io-registers"><h1>IO Registers</h1></a>
|
||||
<p>The GBA has a large number of <strong>IO Registers</strong> (not to be confused with CPU
|
||||
registers). These are special memory locations from <code>0x04000000</code> to
|
||||
<code>0x040003FE</code>. GBATEK has a <a href="http://problemkaputt.de/gbatek.htm#gbaiomap">full
|
||||
list</a>, but we only need to learn
|
||||
about a few of them at a time as we go, so don't be worried.</p>
|
||||
<p>The important facts to know about IO Registers are these:</p>
|
||||
<ul>
|
||||
<li>Each has their own specific size. Most are <code>u16</code>, but some are <code>u32</code>.</li>
|
||||
<li>All of them must be accessed in a <code>volatile</code> style.</li>
|
||||
<li>Each register is specifically readable or writable or both. Actually, with
|
||||
some registers there are even individual bits that are read-only or
|
||||
write-only.
|
||||
<ul>
|
||||
<li>If you write to a read-only position, those writes are simply ignored. This
|
||||
mostly matters if a writable register contains a read-only bit (such as the
|
||||
Display Control, next section).</li>
|
||||
<li>If you read from a write-only position, you get back values that are
|
||||
<a href="http://problemkaputt.de/gbatek.htm#gbaunpredictablethings">basically
|
||||
nonsense</a>. There
|
||||
aren't really any registers that mix writable bits with read only bits, so
|
||||
you're basically safe here. The only (mild) concern is that when you write a
|
||||
value into a write-only register you need to keep track of what you wrote
|
||||
somewhere else if you want to know what you wrote (such to adjust an offset
|
||||
value by +1, or whatever).</li>
|
||||
<li>You can always check GBATEK to be sure, but if I don't mention it then a bit
|
||||
is probably both read and write.</li>
|
||||
</ul>
|
||||
</li>
|
||||
<li>Some registers have invalid bit patterns. For example, the lowest three bits
|
||||
of the Display Control register can't legally be set to the values 6 or 7.</li>
|
||||
</ul>
|
||||
<p>When talking about bit positions, the numbers are <em>zero indexed</em> just like an
|
||||
array index is.</p>
|
||||
<a class="header" href="#the-display-control-register" id="the-display-control-register"><h1>The Display Control Register</h1></a>
|
||||
<p>The display control register is our first actual IO Register. GBATEK gives it the
|
||||
shorthand <a href="http://problemkaputt.de/gbatek.htm#lcdiodisplaycontrol">DISPCNT</a>, so
|
||||
you might see it under that name if you read other guides.</p>
|
||||
<p>Among IO Registers, it's one of the simpler ones, but it's got enough complexity
|
||||
that we can get a hint of what's to come.</p>
|
||||
<p>Also it's the one that you basically always need to set at least once in every
|
||||
GBA game, so it's a good starting one to go over for that reason too.</p>
|
||||
<p>The display control register holds a <code>u16</code> value, and is located at <code>0x0400_0000</code>.</p>
|
||||
<p>Many of the bits here won't mean much to you right now. <strong>That is fine.</strong> You do
|
||||
NOT need to memorize them all or what they all do right away. We'll just skim
|
||||
over all the parts of this register to start, and then we'll go into more detail
|
||||
in later chapters when we need to come back and use more of the bits.</p>
|
||||
<a class="header" href="#video-modes" id="video-modes"><h2>Video Modes</h2></a>
|
||||
<p>The lowest three bits (0-2) let you select from among the GBA's six video modes.
|
||||
You'll notice that 3 bits allows for eight modes, but the values 6 and 7 are
|
||||
prohibited.</p>
|
||||
<p>Modes 0, 1, and 2 are "tiled" modes. These are actually the modes that you
|
||||
should eventually learn to use as much as possible. It lets the GBA's limited
|
||||
video hardware do as much of the work as possible, leaving more of your CPU time
|
||||
for gameplay computations. However, they're also complex enough to deserve their
|
||||
own demos and chapters later on, so that's all we'll say about them for now.</p>
|
||||
<p>Modes 3, 4, and 5 are "bitmap" modes. These let you write individual pixels to
|
||||
locations on the screen.</p>
|
||||
<ul>
|
||||
<li><strong>Mode 3</strong> is full resolution (240w x 160h) RGB15 color. You might not be used
|
||||
to RGB15, since modern computers have 24 or 32 bit colors. In RGB15, there's 5
|
||||
bits for each color channel stored within a <code>u16</code> value, and the highest bit is
|
||||
simply ignored.</li>
|
||||
<li><strong>Mode 4</strong> is full resolution paletted color. Instead of being a <code>u16</code> color, each
|
||||
pixel value is a <code>u8</code> palette index entry, and then the display uses the
|
||||
palette memory (which we'll talk about later) to store the actual color data.
|
||||
Since each pixel is half sized, we can fit twice as many. This lets us have
|
||||
two "pages". At any given moment only one page is active, and you can draw to
|
||||
the other page without the user noticing. You set which page to show with
|
||||
another bit we'll get to in a moment.</li>
|
||||
<li><strong>Mode 5</strong> is full color, but also with pages. This means that we must have a
|
||||
reduced resolution to compensate (video memory is only so big!). The screen is
|
||||
effectively only 160w x 128h in this mode.</li>
|
||||
</ul>
|
||||
<a class="header" href="#cgb-mode" id="cgb-mode"><h2>CGB Mode</h2></a>
|
||||
<p>Bit 3 is effectively read only. Technically it can be flipped using a BIOS call,
|
||||
but when you write to the display control register normally it won't write to
|
||||
this bit, so we'll call it effectively read only.</p>
|
||||
<p>This bit is on if the CPU is in CGB mode.</p>
|
||||
<a class="header" href="#page-flipping" id="page-flipping"><h2>Page Flipping</h2></a>
|
||||
<p>Bit 4 lets you pick which page to use. This is only relevent in video modes 4 or
|
||||
5, and is just ignored otherwise. It's very easy to remember: when the bit is 0
|
||||
the 0th page is used, and when the bit is 1 the 1st page is used.</p>
|
||||
<p>The second page always starts at <code>0x0600_A000</code>.</p>
|
||||
<a class="header" href="#oam-vram-and-blanking" id="oam-vram-and-blanking"><h2>OAM, VRAM, and Blanking</h2></a>
|
||||
<p>Bit 5 lets you access OAM during HBlank if enabled. This is cool, but it reduces
|
||||
the maximum sprites per scanline, so it's not default.</p>
|
||||
<p>Bit 6 lets you adjust if the GBA should treat Object Character VRAM as being 2d
|
||||
(off) or 1d (on). This particular control can be kinda tricky to wrap your head
|
||||
around, so we'll be sure to have some extra diagrams in the chapter that deals
|
||||
with it.</p>
|
||||
<p>Bit 7 forces the screen to stay in vblank as long as it's set. This allows the
|
||||
fastest use of the VRAM, Palette, and Object Attribute Memory. Obviously if you
|
||||
leave this on for too long the player will notice a blank screen, but it might
|
||||
be okay to use for a moment or two every once in a while.</p>
|
||||
<a class="header" href="#screen-layers" id="screen-layers"><h2>Screen Layers</h2></a>
|
||||
<p>Bits 8 through 11 control if Background layers 0 through 3 should be active.</p>
|
||||
<p>Bit 12 affects the Object layer.</p>
|
||||
<p>Note that not all background layers are available in all video modes:</p>
|
||||
<ul>
|
||||
<li>Mode 0: all</li>
|
||||
<li>Mode 1: 0/1/2</li>
|
||||
<li>Mode 2: 2/3</li>
|
||||
<li>Mode 3/4/5: 2</li>
|
||||
</ul>
|
||||
<p>Bit 13 and 14 enable the display of Windows 0 and 1, and Bit 15 enables the
|
||||
object display window. We'll get into how windows work later on, they let you do
|
||||
some nifty graphical effects.</p>
|
||||
<a class="header" href="#in-conclusion" id="in-conclusion"><h2>In Conclusion...</h2></a>
|
||||
<p>So what did we do to the display control register in <code>hello1</code>?</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
(0x04000000 as *mut u16).write_volatile(0x0403);
|
||||
#}</code></pre></pre>
|
||||
<p>First let's <a href="https://www.wolframalpha.com/input/?i=0x0403">convert that to
|
||||
binary</a>, and we get
|
||||
<code>0b100_0000_0011</code>. So, that's setting Mode 3 with background 2 enabled and
|
||||
nothing else special.</p>
|
||||
<p>However, I think we can do better than that. This is a prime target for more
|
||||
newtyping as we attempt a <code>hello2</code> program.</p>
|
||||
<a class="header" href="#video-memory-intro" id="video-memory-intro"><h1>Video Memory Intro</h1></a>
|
||||
<p>The GBA's Video RAM is 96k stretching from <code>0x0600_0000</code> to <code>0x0601_7FFF</code>.</p>
|
||||
<p>The Video RAM can only be accessed totally freely during a Vertical Blank
|
||||
(aka "vblank"). At other times, if the CPU tries to touch the same part of video
|
||||
memory as the display controller is accessing then the CPU gets bumped by a
|
||||
cycle to avoid a clash.</p>
|
||||
<p>Annoyingly, VRAM can only be properly written to in 16 and 32 bit segments (same
|
||||
with PALRAM and OAM). If you try to write just an 8 bit segment, then both parts
|
||||
of the 16 bit segment get the same value written to them. In other words, if you
|
||||
write the byte <code>5</code> to <code>0x0600_0000</code>, then both <code>0x0600_0000</code> and ALSO
|
||||
<code>0x0600_0001</code> will have the byte <code>5</code> in them. We have to be extra careful when
|
||||
trying to set an individual byte, and we also have to be careful if we use
|
||||
<code>memcopy</code> or <code>memset</code> as well, because they're byte oriented by default and
|
||||
don't know to follow the special rules.</p>
|
||||
<a class="header" href="#rgb15" id="rgb15"><h2>RGB15</h2></a>
|
||||
<p>As I said before, RGB15 stores a color within a <code>u16</code> value using 5 bits for
|
||||
each color channel.</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
pub const RED: u16 = 0b0_00000_00000_11111;
|
||||
pub const GREEN: u16 = 0b0_00000_11111_00000;
|
||||
pub const BLUE: u16 = 0b0_11111_00000_00000;
|
||||
#}</code></pre></pre>
|
||||
<p>In Mode 3 and Mode 5 we write direct color values into VRAM, and in Mode 4 we
|
||||
write palette index values, and then the color values go into the PALRAM.</p>
|
||||
<a class="header" href="#mode-3" id="mode-3"><h2>Mode 3</h2></a>
|
||||
<p>Mode 3 is pretty easy. We have a full resolution grid of rgb15 pixels. There's
|
||||
160 rows of 240 pixels each, with the base address being the top left corner. A
|
||||
particular pixel uses normal "2d indexing" math:</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
let row_five_col_seven = 5 + (7 * SCREEN_WIDTH);
|
||||
#}</code></pre></pre>
|
||||
<p>To draw a pixel, we just write a value at the address for the row and col that
|
||||
we want to draw to.</p>
|
||||
<a class="header" href="#mode-4" id="mode-4"><h2>Mode 4</h2></a>
|
||||
<p>Mode 4 introduces page flipping. Instead of one giant page at <code>0x0600_0000</code>,
|
||||
there's Page 0 at <code>0x0600_0000</code> and then Page 1 at <code>0x0600_A000</code>. The resolution
|
||||
for each page is the same as above, but instead of writing <code>u16</code> values, the
|
||||
memory is treated as <code>u8</code> indexes into PALRAM. The PALRAM starts at
|
||||
<code>0x0500_0000</code>, and there's enough space for 256 palette entries (each a <code>u16</code>).</p>
|
||||
<p>To set the color of a palette entry we just do a normal <code>u16</code> write_volatile.</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
(0x0500_0000 as *mut u16).offset(target_index).write_volatile(new_color)
|
||||
#}</code></pre></pre>
|
||||
<p>To draw a pixel we set the palette entry that we want the pixel to use. However,
|
||||
we must remember the "minimum size" write limitation that applies to VRAM. So,
|
||||
if we want to change just a single pixel at a time we must</p>
|
||||
<ol>
|
||||
<li>Read the full <code>u16</code> it's a part of.</li>
|
||||
<li>Clear the half of the <code>u16</code> we're going to replace</li>
|
||||
<li>Write the half of the <code>u16</code> we're going to replace with the new value</li>
|
||||
<li>Write that result back to the address.</li>
|
||||
</ol>
|
||||
<p>So, the math for finding a byte offset is the same as Mode 3 (since they're both
|
||||
a 2d grid). If the byte offset is EVEN it'll be the high bits of the <code>u16</code> at
|
||||
half the byte offset rounded down. If the offset is ODD it'll be the low bits of
|
||||
the <code>u16</code> at half the byte.</p>
|
||||
<p>Does that make sense?</p>
|
||||
<ul>
|
||||
<li>If we want to write pixel (0,0) the byte offset is 0, so we change the high
|
||||
bits of <code>u16</code> offset 0. Then we want to write to (1,0), so the byte offset is
|
||||
1, so we change the low bits of <code>u16</code> offset 0. The pixels are next to each
|
||||
other, and the target bytes are next to each other, good so far.</li>
|
||||
<li>If we want to write to (5,6) that'd be byte <code>5 + 6 * 240 = 1445</code>, so we'd
|
||||
target the low bits of <code>u16</code> offset <code>floor(1445/2) = 722</code>.</li>
|
||||
</ul>
|
||||
<p>As you can see, trying to write individual pixels in Mode 4 is mostly a bad
|
||||
time. Fret not! We don't <em>have</em> to write individual bytes. If our data is
|
||||
arranged correctly ahead of time we can just write <code>u16</code> or <code>u32</code> values
|
||||
directly. The video hardware doesn't care, it'll get along just fine.</p>
|
||||
<a class="header" href="#mode-5" id="mode-5"><h2>Mode 5</h2></a>
|
||||
<p>Mode 5 is also a two page mode, but instead of compressing the size of a pixel's
|
||||
data to fit in two pages, we compress the resolution.</p>
|
||||
<p>Mode 5 is full <code>u16</code> color, but only 160w x 128h per page.</p>
|
||||
<a class="header" href="#in-conclusion-1" id="in-conclusion-1"><h2>In Conclusion...</h2></a>
|
||||
<p>So what got written into VRAM in <code>hello1</code>?</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
(0x06000000 as *mut u16).offset(120 + 80 * 240).write_volatile(0x001F);
|
||||
(0x06000000 as *mut u16).offset(136 + 80 * 240).write_volatile(0x03E0);
|
||||
(0x06000000 as *mut u16).offset(120 + 96 * 240).write_volatile(0x7C00);
|
||||
#}</code></pre></pre>
|
||||
<p>So at pixels <code>(120,80)</code>, <code>(136,80)</code>, and <code>(120,96)</code> we write three values. Once
|
||||
again we probably need to <a href="https://www.wolframalpha.com/">convert them</a> into
|
||||
binary to make sense of it.</p>
|
||||
<ul>
|
||||
<li>0x001F: 0b11111</li>
|
||||
<li>0x03E0: 0b11111_00000</li>
|
||||
<li>0x7C00: 0b11111_00000_00000</li>
|
||||
</ul>
|
||||
<p>Ah, of course, a red pixel, a green pixel, and a blue pixel.</p>
|
||||
<a class="header" href="#hello2" id="hello2"><h1>hello2</h1></a>
|
||||
<p>Okay so let's have a look again:</p>
|
||||
<p><code>hello1</code></p>
|
||||
<pre><pre class="playpen"><code class="language-rust">#![feature(start)]
|
||||
#![no_std]
|
||||
|
||||
#[cfg(not(test))]
|
||||
#[panic_handler]
|
||||
fn panic(_info: &core::panic::PanicInfo) -> ! {
|
||||
loop {}
|
||||
}
|
||||
|
||||
#[start]
|
||||
fn main(_argc: isize, _argv: *const *const u8) -> isize {
|
||||
unsafe {
|
||||
(0x04000000 as *mut u16).write_volatile(0x0403);
|
||||
(0x06000000 as *mut u16).offset(120 + 80 * 240).write_volatile(0x001F);
|
||||
(0x06000000 as *mut u16).offset(136 + 80 * 240).write_volatile(0x03E0);
|
||||
(0x06000000 as *mut u16).offset(120 + 96 * 240).write_volatile(0x7C00);
|
||||
loop {}
|
||||
}
|
||||
}
|
||||
</code></pre></pre>
|
||||
<p>Now let's clean this up so that it's clearer what's going on.</p>
|
||||
<p>First we'll label that display control stuff:</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
pub const DISPCNT: *mut u16 = 0x04000000 as *mut u16;
|
||||
pub const MODE3: u16 = 3;
|
||||
pub const BG2: u16 = 0b100_0000_0000;
|
||||
#}</code></pre></pre>
|
||||
<p>Next we make some const values for the actual pixel drawing</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
pub const VRAM: usize = 0x06000000;
|
||||
pub const SCREEN_WIDTH: isize = 240;
|
||||
#}</code></pre></pre>
|
||||
<p>And then we want a small helper function for putting together a color value.</p>
|
||||
<p>Happily, this one can even be declared as a const function. At the time of
|
||||
writing, we've got the "minimal const fn" support in nightly. It really is quite
|
||||
limited, but I'm happy to let rustc and LLVM pre-compute as much as they can
|
||||
when it comes to the GBA's tiny CPU.</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
pub const fn rgb16(red: u16, green: u16, blue: u16) -> u16 {
|
||||
blue << 10 | green << 5 | red
|
||||
}
|
||||
#}</code></pre></pre>
|
||||
<p>Finally, we'll make a function for drawing a pixel in Mode 3. Even though it's
|
||||
just a one-liner, having the "important parts" be labeled as function arguments
|
||||
usually helps you think about it a lot better.</p>
|
||||
<pre><pre class="playpen"><code class="language-rust">
|
||||
# #![allow(unused_variables)]
|
||||
#fn main() {
|
||||
pub unsafe fn mode3_pixel(col: isize, row: isize, color: u16) {
|
||||
(VRAM as *mut u16).offset(col + row * SCREEN_WIDTH).write_volatile(color);
|
||||
}
|
||||
#}</code></pre></pre>
|
||||
<p>So now we've got this:</p>
|
||||
<p><code>hello2</code></p>
|
||||
<pre><pre class="playpen"><code class="language-rust">#![feature(start)]
|
||||
#![no_std]
|
||||
|
||||
#[cfg(not(test))]
|
||||
#[panic_handler]
|
||||
fn panic(_info: &core::panic::PanicInfo) -> ! {
|
||||
loop {}
|
||||
}
|
||||
|
||||
#[start]
|
||||
fn main(_argc: isize, _argv: *const *const u8) -> isize {
|
||||
unsafe {
|
||||
DISPCNT.write_volatile(MODE3 | BG2);
|
||||
mode3_pixel(120, 80, rgb16(31, 0, 0));
|
||||
mode3_pixel(136, 80, rgb16(0, 31, 0));
|
||||
mode3_pixel(120, 96, rgb16(0, 0, 31));
|
||||
loop {}
|
||||
}
|
||||
}
|
||||
|
||||
pub const DISPCNT: *mut u16 = 0x04000000 as *mut u16;
|
||||
pub const MODE3: u16 = 3;
|
||||
pub const BG2: u16 = 0b100_0000_0000;
|
||||
|
||||
pub const VRAM: usize = 0x06000000;
|
||||
pub const SCREEN_WIDTH: isize = 240;
|
||||
|
||||
pub const fn rgb16(red: u16, green: u16, blue: u16) -> u16 {
|
||||
blue << 10 | green << 5 | red
|
||||
}
|
||||
|
||||
pub unsafe fn mode3_pixel(col: isize, row: isize, color: u16) {
|
||||
(VRAM as *mut u16).offset(col + row * SCREEN_WIDTH).write_volatile(color);
|
||||
}
|
||||
</code></pre></pre>
|
||||
<p>Exact same program that we started with, but much easier to read.</p>
|
||||
<p>Of course, in the full <code>gba</code> crate that this book is a part of we have these and
|
||||
other elements all labeled and sorted out for you. Still, for educational
|
||||
purposes it's often best to do it yourself at least once.</p>
|
||||
|
||||
</main>
|
||||
|
||||
|
|
|
|||
File diff suppressed because one or more lines are too long
File diff suppressed because one or more lines are too long
19
examples/hello1.rs
Normal file
19
examples/hello1.rs
Normal file
|
|
@ -0,0 +1,19 @@
|
|||
#![feature(start)]
|
||||
#![no_std]
|
||||
|
||||
#[cfg(not(test))]
|
||||
#[panic_handler]
|
||||
fn panic(_info: &core::panic::PanicInfo) -> ! {
|
||||
loop {}
|
||||
}
|
||||
|
||||
#[start]
|
||||
fn main(_argc: isize, _argv: *const *const u8) -> isize {
|
||||
unsafe {
|
||||
(0x04000000 as *mut u16).write_volatile(0x0403);
|
||||
(0x06000000 as *mut u16).offset(120 + 80 * 240).write_volatile(0x001F);
|
||||
(0x06000000 as *mut u16).offset(136 + 80 * 240).write_volatile(0x03E0);
|
||||
(0x06000000 as *mut u16).offset(120 + 96 * 240).write_volatile(0x7C00);
|
||||
loop {}
|
||||
}
|
||||
}
|
||||
34
examples/hello2.rs
Normal file
34
examples/hello2.rs
Normal file
|
|
@ -0,0 +1,34 @@
|
|||
#![feature(start)]
|
||||
#![no_std]
|
||||
|
||||
#[cfg(not(test))]
|
||||
#[panic_handler]
|
||||
fn panic(_info: &core::panic::PanicInfo) -> ! {
|
||||
loop {}
|
||||
}
|
||||
|
||||
#[start]
|
||||
fn main(_argc: isize, _argv: *const *const u8) -> isize {
|
||||
unsafe {
|
||||
DISPCNT.write_volatile(MODE3 | BG2);
|
||||
mode3_pixel(120, 80, rgb16(31, 0, 0));
|
||||
mode3_pixel(136, 80, rgb16(0, 31, 0));
|
||||
mode3_pixel(120, 96, rgb16(0, 0, 31));
|
||||
loop {}
|
||||
}
|
||||
}
|
||||
|
||||
pub const DISPCNT: *mut u16 = 0x04000000 as *mut u16;
|
||||
pub const MODE3: u16 = 3;
|
||||
pub const BG2: u16 = 0b100_0000_0000;
|
||||
|
||||
pub const VRAM: usize = 0x06000000;
|
||||
pub const SCREEN_WIDTH: isize = 240;
|
||||
|
||||
pub const fn rgb16(red: u16, green: u16, blue: u16) -> u16 {
|
||||
blue << 10 | green << 5 | red
|
||||
}
|
||||
|
||||
pub unsafe fn mode3_pixel(col: isize, row: isize, color: u16) {
|
||||
(VRAM as *mut u16).offset(col + row * SCREEN_WIDTH).write_volatile(color);
|
||||
}
|
||||
63
linker.ld
Normal file
63
linker.ld
Normal file
|
|
@ -0,0 +1,63 @@
|
|||
ENTRY(__start)
|
||||
|
||||
MEMORY {
|
||||
ewram (w!x) : ORIGIN = 0x2000000, LENGTH = 256K
|
||||
iwram (w!x) : ORIGIN = 0x3000000, LENGTH = 32K
|
||||
rom (rx) : ORIGIN = 0x8000000, LENGTH = 32M
|
||||
}
|
||||
|
||||
SECTIONS {
|
||||
.text : {
|
||||
KEEP(crt0.o(.text));
|
||||
*(.text .text.*);
|
||||
. = ALIGN(4);
|
||||
} >rom = 0xff
|
||||
|
||||
.rodata : {
|
||||
*(.rodata .rodata.*);
|
||||
. = ALIGN(4);
|
||||
} >rom = 0xff
|
||||
|
||||
__data_lma = .;
|
||||
.data : {
|
||||
__data_start = ABSOLUTE(.);
|
||||
*(.data .data.*);
|
||||
. = ALIGN(4);
|
||||
__data_end = ABSOLUTE(.);
|
||||
} >iwram AT>rom = 0xff
|
||||
|
||||
/* debugging sections */
|
||||
/* Stabs */
|
||||
.stab 0 : { *(.stab) }
|
||||
.stabstr 0 : { *(.stabstr) }
|
||||
.stab.excl 0 : { *(.stab.excl) }
|
||||
.stab.exclstr 0 : { *(.stab.exclstr) }
|
||||
.stab.index 0 : { *(.stab.index) }
|
||||
.stab.indexstr 0 : { *(.stab.indexstr) }
|
||||
.comment 0 : { *(.comment) }
|
||||
/* DWARF 1 */
|
||||
.debug 0 : { *(.debug) }
|
||||
.line 0 : { *(.line) }
|
||||
/* GNU DWARF 1 extensions */
|
||||
.debug_srcinfo 0 : { *(.debug_srcinfo) }
|
||||
.debug_sfnames 0 : { *(.debug_sfnames) }
|
||||
/* DWARF 1.1 and DWARF 2 */
|
||||
.debug_aranges 0 : { *(.debug_aranges) }
|
||||
.debug_pubnames 0 : { *(.debug_pubnames) }
|
||||
/* DWARF 2 */
|
||||
.debug_info 0 : { *(.debug_info) }
|
||||
.debug_abbrev 0 : { *(.debug_abbrev) }
|
||||
.debug_line 0 : { *(.debug_line) }
|
||||
.debug_frame 0 : { *(.debug_frame) }
|
||||
.debug_str 0 : { *(.debug_str) }
|
||||
.debug_loc 0 : { *(.debug_loc) }
|
||||
.debug_macinfo 0 : { *(.debug_macinfo) }
|
||||
/* SGI/MIPS DWARF 2 extensions */
|
||||
.debug_weaknames 0 : { *(.debug_weaknames) }
|
||||
.debug_funcnames 0 : { *(.debug_funcnames) }
|
||||
.debug_typenames 0 : { *(.debug_typenames) }
|
||||
.debug_varnames 0 : { *(.debug_varnames) }
|
||||
|
||||
/* discard anything not already mentioned */
|
||||
/DISCARD/ : { *(*) }
|
||||
}
|
||||
|
|
@ -1,13 +1,13 @@
|
|||
//! Things that I wish were in core, but aren't.
|
||||
|
||||
#[derive(Debug, Clone, Copy, Hash, PartialEq, Eq, PartialOrd, Ord)]
|
||||
#[repr(transparent)]
|
||||
/// A simple wrapper to any `*mut T` so that the basic "read" and "write"
|
||||
/// operations are volatile.
|
||||
///
|
||||
/// Accessing the GBA's IO registers and video ram and specific other places on
|
||||
/// **must** be done with volatile operations. Having this wrapper makes that
|
||||
/// more clear for all the global const values into IO registers.
|
||||
#[derive(Debug, Clone, Copy, Hash, PartialEq, Eq, PartialOrd, Ord)]
|
||||
#[repr(transparent)]
|
||||
pub struct VolatilePtr<T>(pub *mut T);
|
||||
|
||||
impl<T> core::fmt::Pointer for VolatilePtr<T> {
|
||||
|
|
@ -37,4 +37,14 @@ impl<T> VolatilePtr<T> {
|
|||
pub unsafe fn write(&self, data: T) {
|
||||
core::ptr::write_volatile(self.0, data);
|
||||
}
|
||||
|
||||
/// Offsets this address by the amount given.
|
||||
///
|
||||
/// # Safety
|
||||
///
|
||||
/// This is a standard offset, so all safety concerns of a normal raw pointer
|
||||
/// offset apply.
|
||||
pub unsafe fn offset(self, count: isize) -> Self {
|
||||
VolatilePtr(self.0.offset(count))
|
||||
}
|
||||
}
|
||||
|
|
|
|||
|
|
@ -15,6 +15,8 @@
|
|||
|
||||
// TODO(lokathor): IO Register newtypes.
|
||||
|
||||
use gba_proc_macro::register_bit;
|
||||
|
||||
use super::*;
|
||||
|
||||
/// LCD Control. Read/Write.
|
||||
|
|
@ -22,8 +24,85 @@ use super::*;
|
|||
/// * [gbatek entry](http://problemkaputt.de/gbatek.htm#lcdiodisplaycontrol)
|
||||
pub const DISPCNT: VolatilePtr<u16> = VolatilePtr(0x4000000 as *mut u16);
|
||||
|
||||
/// Undocumented - Green Swap
|
||||
pub const GREEN_SWAP: VolatilePtr<u16> = VolatilePtr(0x4000002 as *mut u16);
|
||||
/// A newtype over the various display control options that you have on a GBA.
|
||||
#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
|
||||
#[repr(transparent)]
|
||||
pub struct DisplayControlSetting(u16);
|
||||
|
||||
#[allow(missing_docs)]
|
||||
impl DisplayControlSetting {
|
||||
pub const BG_MODE_MASK: u16 = 0b111;
|
||||
|
||||
pub fn mode(&self) -> DisplayControlMode {
|
||||
match self.0 & Self::BG_MODE_MASK {
|
||||
0 => DisplayControlMode::Tiled0,
|
||||
1 => DisplayControlMode::Tiled1,
|
||||
2 => DisplayControlMode::Tiled2,
|
||||
3 => DisplayControlMode::Bitmap3,
|
||||
4 => DisplayControlMode::Bitmap4,
|
||||
5 => DisplayControlMode::Bitmap5,
|
||||
_ => unreachable!(),
|
||||
}
|
||||
}
|
||||
pub fn set_mode(&mut self, new_mode: DisplayControlMode) {
|
||||
self.0 &= !Self::BG_MODE_MASK;
|
||||
self.0 |= match new_mode {
|
||||
DisplayControlMode::Tiled0 => 0,
|
||||
DisplayControlMode::Tiled1 => 1,
|
||||
DisplayControlMode::Tiled2 => 2,
|
||||
DisplayControlMode::Bitmap3 => 3,
|
||||
DisplayControlMode::Bitmap4 => 4,
|
||||
DisplayControlMode::Bitmap5 => 5,
|
||||
};
|
||||
}
|
||||
|
||||
register_bit!(CGB_MODE_BIT, u16, 0b1000, cgb_mode, read);
|
||||
register_bit!(PAGE_SELECT_BIT, u16, 0b1_0000, page1_enabled, read_write);
|
||||
register_bit!(HBLANK_INTERVAL_FREE_BIT, u16, 0b10_0000, hblank_interval_free, read_write);
|
||||
register_bit!(OBJECT_MEMORY_1D, u16, 0b100_0000, object_memory_1d, read_write);
|
||||
register_bit!(FORCE_BLANK_BIT, u16, 0b1000_0000, force_blank, read_write);
|
||||
register_bit!(DISPLAY_BG0_BIT, u16, 0b1_0000_0000, display_bg0, read_write);
|
||||
register_bit!(DISPLAY_BG1_BIT, u16, 0b10_0000_0000, display_bg1, read_write);
|
||||
register_bit!(DISPLAY_BG2_BIT, u16, 0b100_0000_0000, display_bg2, read_write);
|
||||
register_bit!(DISPLAY_BG3_BIT, u16, 0b1000_0000_0000, display_bg3, read_write);
|
||||
register_bit!(DISPLAY_OBJECT_BIT, u16, 0b1_0000_0000_0000, display_object, read_write);
|
||||
register_bit!(DISPLAY_WINDOW0_BIT, u16, 0b10_0000_0000_0000, display_window0, read_write);
|
||||
register_bit!(DISPLAY_WINDOW1_BIT, u16, 0b100_0000_0000_0000, display_window1, read_write);
|
||||
register_bit!(OBJECT_WINDOW_BIT, u16, 0b1000_0000_0000_0000, display_object_window, read_write);
|
||||
}
|
||||
|
||||
/// The six display modes available on the GBA.
|
||||
pub enum DisplayControlMode {
|
||||
/// This basically allows for the most different things at once (all layers,
|
||||
/// 1024 tiles, two palette modes, etc), but you can't do affine
|
||||
/// transformations.
|
||||
Tiled0,
|
||||
/// This is a mix of `Tile0` and `Tile2`: BG0 and BG1 run as if in `Tiled0`,
|
||||
/// and BG2 runs as if in `Tiled2`.
|
||||
Tiled1,
|
||||
/// This allows affine transformations, but only uses BG2 and BG3.
|
||||
Tiled2,
|
||||
/// This is the basic bitmap draw mode. The whole screen is a single bitmap.
|
||||
/// Uses BG2 only.
|
||||
Bitmap3,
|
||||
/// This uses _paletted color_ so that there's enough space to have two pages
|
||||
/// at _full resolution_, allowing page flipping. Uses BG2 only.
|
||||
Bitmap4,
|
||||
/// This uses _reduced resolution_ so that there's enough space to have two
|
||||
/// pages with _full color_, allowing page flipping. Uses BG2 only.
|
||||
Bitmap5,
|
||||
}
|
||||
|
||||
/// Assigns the given display control setting.
|
||||
pub fn set_display_control(setting: DisplayControlSetting) {
|
||||
unsafe {
|
||||
DISPCNT.write(setting.0);
|
||||
}
|
||||
}
|
||||
/// Obtains the current display control setting.
|
||||
pub fn display_control() -> DisplayControlSetting {
|
||||
unsafe { DisplayControlSetting(DISPCNT.read()) }
|
||||
}
|
||||
|
||||
/// General LCD Status (STAT,LYC)
|
||||
pub const DISPSTAT: VolatilePtr<u16> = VolatilePtr(0x4000004 as *mut u16);
|
||||
|
|
@ -333,9 +412,3 @@ pub const WAITCNT: VolatilePtr<u16> = VolatilePtr(0x4000204 as *mut u16);
|
|||
|
||||
/// Interrupt Master Enable Register
|
||||
pub const IME: VolatilePtr<u16> = VolatilePtr(0x4000208 as *mut u16);
|
||||
|
||||
/// Undocumented - Post Boot Flag
|
||||
pub const POSTFLG: VolatilePtr<u8> = VolatilePtr(0x4000300 as *mut u8);
|
||||
|
||||
/// Undocumented - Power Down Control
|
||||
pub const HALTCNT: VolatilePtr<u8> = VolatilePtr(0x4000301 as *mut u8);
|
||||
|
|
|
|||
10
src/lib.rs
10
src/lib.rs
|
|
@ -14,10 +14,14 @@
|
|||
//! **Do not** use this crate in programs that aren't running on the GBA. If you
|
||||
//! do, it's a giant bag of Undefined Behavior.
|
||||
|
||||
//pub mod macros; // un-comment once we get some
|
||||
|
||||
pub mod core_extras;
|
||||
pub(crate) use crate::core_extras::*;
|
||||
|
||||
pub mod io_registers;
|
||||
//pub(crate) use crate::io_registers::*;
|
||||
|
||||
pub mod video_ram;
|
||||
|
||||
/// Combines the Red, Blue, and Green provided into a single color value.
|
||||
pub const fn rgb16(red: u16, green: u16, blue: u16) -> u16 {
|
||||
blue << 10 | green << 5 | red
|
||||
}
|
||||
|
|
|
|||
|
|
@ -1,6 +1,8 @@
|
|||
//! Module for all macros.
|
||||
//!
|
||||
//! Macros are the only thing in rust where declaration order matters, so we
|
||||
//! place all of them here regardless of what they do.
|
||||
//! Macros are the only thing in Rust where declaration order matters, so we
|
||||
//! place all of them here regardless of what they do so that the macros module
|
||||
//! can appear at the "top" of the library and all other modules can see them
|
||||
//! properly.
|
||||
|
||||
// no macros yet!
|
||||
|
|
|
|||
49
src/video_ram.rs
Normal file
49
src/video_ram.rs
Normal file
|
|
@ -0,0 +1,49 @@
|
|||
//! Module for all things relating to the Video RAM.
|
||||
//!
|
||||
//! Note that the GBA has six different display modes available, and the
|
||||
//! _meaning_ of Video RAM depends on which display mode is active. In all
|
||||
//! cases, Video RAM is **96kb** from `0x0600_0000` to `0x0601_7FFF`.
|
||||
//!
|
||||
//! # Safety
|
||||
//!
|
||||
//! Note that all possible bit patterns are technically allowed within Video
|
||||
//! Memory. If you write the "wrong" thing into video memory you don't crash the
|
||||
//! GBA, instead you just get graphical glitches (or perhaps nothing at all).
|
||||
//! Accordingly, the "safe" functions here will check that you're in bounds, but
|
||||
//! they won't bother to check that you've set the video mode they're designed
|
||||
//! for.
|
||||
|
||||
/// The physical width in pixels of the GBA screen.
|
||||
pub const SCREEN_WIDTH: isize = 240;
|
||||
|
||||
/// The physical height in pixels of the GBA screen.
|
||||
pub const SCREEN_HEIGHT: isize = 160;
|
||||
|
||||
/// The start of VRAM.
|
||||
///
|
||||
/// Depending on what display mode is currently set there's different ways that
|
||||
/// your program should interpret the VRAM space. Accordingly, we give the raw
|
||||
/// value as just being a `usize`.
|
||||
pub const VRAM_BASE_ADDRESS: usize = 0x0600_0000;
|
||||
|
||||
/// Draws a pixel to the screen while in Display Mode 3, with bounds checks.
|
||||
pub fn mode3_pixel(col: isize, row: isize, color: u16) {
|
||||
assert!(col >= 0 && col < SCREEN_WIDTH);
|
||||
assert!(row >= 0 && row < SCREEN_HEIGHT);
|
||||
unsafe { mode3_pixel_unchecked(col, row, color) }
|
||||
}
|
||||
|
||||
/// Draws a pixel to the screen while in Display Mode 3.
|
||||
///
|
||||
/// Coordinates are relative to the top left corner.
|
||||
///
|
||||
/// If you're in another mode you'll get something weird drawn, but it's memory
|
||||
/// safe in the rust sense as long as you stay in bounds.
|
||||
///
|
||||
/// # Safety
|
||||
///
|
||||
/// * `col` must be in `0..SCREEN_WIDTH`
|
||||
/// * `row` must be in `0..SCREEN_HEIGHT`
|
||||
pub unsafe fn mode3_pixel_unchecked(col: isize, row: isize, color: u16) {
|
||||
core::ptr::write_volatile((VRAM_BASE_ADDRESS as *mut u16).offset(col + row * SCREEN_WIDTH), color);
|
||||
}
|
||||
|
|
@ -18,7 +18,7 @@
|
|||
"linker": "arm-none-eabi-ld",
|
||||
"linker-flavor": "ld",
|
||||
"linker-is-gnu": true,
|
||||
"llvm-target": "thumbv4-none-eabi",
|
||||
"llvm-target": "thumbv4-none-agb",
|
||||
"os": "none",
|
||||
"panic-strategy": "abort",
|
||||
"pre-link-args": {
|
||||
Loading…
Reference in a new issue