gb-emu/src/main.rs

#![feature(exclusive_range_pattern)]

mod processor;

use clap::{ArgGroup, Parser};
use minifb::{Window, WindowOptions};
use processor::CPU;
use std::{
    fs,
    io::{self, stdout, Write},
    sync::RwLock,
};

use crate::processor::Registers;

#[macro_export]
macro_rules! verbose_println {
    ($($tts:tt)*) => {
            if crate::is_verbose() {
                    println!($($tts)*);
            }
    };
}

#[macro_export]
macro_rules! verbose_print {
    ($($tts:tt)*) => {
            if crate::is_verbose() {
                    print!($($tts)*);
            }
    };
}

/// Simple program to greet a person
#[derive(Parser, Debug)]
#[command(author, version, about, long_about = None)]
#[command(group(ArgGroup::new("prints").args(["verbose","cycle_count"])))]
struct Args {
    /// ROM path
    #[arg(short, long)]
    rom: String,

    /// BootROM path
    #[arg(short, long)]
    bootrom: String,

    /// Just run BootROM
    #[arg(long)]
    run_bootrom: bool,

    /// Verbose print
    #[arg(short, long)]
    verbose: bool,

    /// Show cycle count
    #[arg(short, long)]
    cycle_count: bool,

    /// Step emulation by...
    #[arg(long)]
    step_by: Option<usize>,
}

type Address = u16;
type ROM = Vec<u8>;

#[allow(dead_code)]
pub struct Memory {
    bootrom: ROM,
    bootrom_enabled: bool,
    interrupt_table: [u8; 256],
    rom: ROM,
    vram: [u8; 8192],
    ram: [u8; 8192],
    switchable_ram: [u8; 8192],
    cpu_ram: [u8; 128],
    oam: [u8; 160],
    interrupts: u8,
    ime: bool,
    ime_scheduled: u8,
    io: [u8; 76],
}

impl Memory {
    fn init(bootrom: ROM, bootrom_enabled: bool, rom: ROM) -> Self {
        Self {
            bootrom,
            bootrom_enabled,
            interrupt_table: [0xFF; 256],
            rom,
            vram: [0x0; 8192],
            ram: [0x0; 8192],
            switchable_ram: [0x0; 8192],
            cpu_ram: [0x0; 128],
            oam: [0x0; 160],
            interrupts: 0x0,
            ime: false,
            ime_scheduled: 0x0,
            io: [0xFF; 76],
        }
    }

    fn get(&self, address: Address) -> u8 {
        match address {
            0x0..0x100 => {
                if self.bootrom_enabled {
                    return self.bootrom[address as usize];
                } else {
                    return self.interrupt_table[address as usize];
                }
            }
            0x100..0x8000 => {
                // rom access
                // todo - switchable rom banks
                if self.bootrom_enabled && (address as usize) < self.bootrom.len() {
                    return self.bootrom[address as usize];
                } else {
                    return self.rom[address as usize];
                }
            }
            0x8000..0xA000 => {
                return self.vram[(address - 0x8000) as usize];
            }
            0xA000..0xC000 => 0xFF,
            0xC000..0xE000 => {
                return self.ram[(address - 0xC000) as usize];
            }
            0xE000..0xFE00 => {
                return self.ram[(address - 0xE000) as usize];
            }
            0xFE00..0xFEA0 => {
                return self.oam[(address - 0xFE00) as usize];
            }
            0xFEA0..0xFF00 => {
                return 0x0;
            }
            0xFF00..0xFF4C => {
                return self.io[(address - 0xFF00) as usize];
            }
            0xFF4C..0xFF80 => {
                // println!("empty space 2 read");
                return 0xFF;
            }
            0xFF80..0xFFFF => {
                return self.cpu_ram[(address - 0xFF80) as usize];
            }
            0xFFFF => {
                return self.interrupts;
            }
        }
    }

    fn set(&mut self, address: Address, data: u8) {
        verbose_println!("write addr: {:#X}, data: {:#X}", address, data);

        match address {
            0x0..0x100 => {
                if !self.bootrom_enabled {
                    self.interrupt_table[address as usize] = data;
                    // panic!("setting {:#X} to {:#X}", address, data)
                }
            }
            0x100..0x8000 => {
                // change this with MBC code...
                // println!("tried to write {:#5X} at {:#X}", data, address);
            }
            0x8000..0xA000 => {
                self.vram[(address - 0x8000) as usize] = data;
            }
            0xA000..0xC000 => {
                // panic!("switchable write");
                // self.switchable_ram[(address - 0xA000) as usize] = data;
            }
            0xC000..0xE000 => {
                self.ram[(address - 0xC000) as usize] = data;
            }
            0xE000..0xFE00 => {
                self.ram[(address - 0xE000) as usize] = data;
            }
            0xFE00..0xFEA0 => {
                self.oam[(address - 0xFE00) as usize] = data;
            }
            0xFEA0..0xFF00 => {
                // println!("empty space write: {:#X} to addr {:#X}", data, address);
            }
            0xFF00..0xFF4C => {
                verbose_print!("writing to addr {:#X}\r", address);
                stdout().flush().unwrap();

                if address == 0xFF02 && data == 0x81 {
                    print!("{}", self.get(0xFF01) as char);
                    stdout().flush().unwrap();
                }
                self.io[(address - 0xFF00) as usize] = data;
            }
            0xFF4C..0xFF80 => {
                // println!("empty space 2 write: {:#X} to addr {:#X}", data, address);
            }
            0xFF80..0xFFFF => {
                self.cpu_ram[(address - 0xFF80) as usize] = data;
            }
            0xFFFF => {
                verbose_println!("interrupts set to {:#b}", data);
                verbose_println!("                / {:#X}", data);
                self.interrupts = data;
            }
        }
    }
}

fn cpu_ram_init(cpu: &mut CPU) {
    cpu.memory.set(0xFF10, 0x80);
    cpu.memory.set(0xFF11, 0xBF);
    cpu.memory.set(0xFF12, 0xF3);
    cpu.memory.set(0xFF14, 0xBF);
    cpu.memory.set(0xFF16, 0x3F);
    cpu.memory.set(0xFF19, 0xBF);
    cpu.memory.set(0xFF1A, 0x7F);
    cpu.memory.set(0xFF1B, 0xFF);
    cpu.memory.set(0xFF1C, 0x9F);
    cpu.memory.set(0xFF1E, 0xBF);
    cpu.memory.set(0xFF20, 0xFF);
    cpu.memory.set(0xFF23, 0xBF);
    cpu.memory.set(0xFF24, 0x77);
    cpu.memory.set(0xFF25, 0xF3);
    cpu.memory.set(0xFF26, 0xF1);
    cpu.memory.set(0xFF40, 0x91);
    cpu.memory.set(0xFF47, 0xFC);
    cpu.memory.set(0xFF48, 0xFF);
    cpu.memory.set(0xFF49, 0xFF);
}

#[allow(dead_code)]
fn swap_rom_endian(rom: &ROM) -> ROM {
    rom.chunks(2)
        .map(|l| {
            let mut m = l.to_owned();
            m.reverse();
            m
        })
        .flatten()
        .collect()
}

static mut PAUSE_ENABLED: bool = false;
static mut PAUSE_QUEUED: bool = false;
// static mut VERBOSE: bool = false;
static VERBOSE: RwLock<bool> = RwLock::new(false);

const WIDTH: usize = 160;
const HEIGHT: usize = 144;

fn main() {
    let args = Args::parse();
    {
        let mut v = VERBOSE.write().unwrap();
        *v = args.verbose;
    }

    let buffer: Vec<u32> = vec![0; WIDTH * HEIGHT];

    let mut window = Window::new("Gameboy", WIDTH, HEIGHT, WindowOptions::default())
        .unwrap_or_else(|e| {
            panic!("{}", e);
        });

    window.update_with_buffer(&buffer, WIDTH, HEIGHT).unwrap();

    let rom: ROM = fs::read(args.rom).expect("Could not load ROM");
    let bootrom: ROM = fs::read(args.bootrom).expect("Could not load BootROM");
    let mut reg = Registers::default();
    if args.run_bootrom {
        reg.pc = 0x0;
    }

    let mut cpu = CPU {
        memory: Memory::init(bootrom, args.run_bootrom, rom),
        reg,
        last_instruction: 0x0,
        last_instruction_addr: 0x0,
        vblank_timer: 0.,
        vblank_remaining: 0,
        window,
        buffer,
    };
    cpu_ram_init(&mut cpu);
    let mut cycle_num = 0;
    let mut instructions_seen = vec![];
    let mut last_state = cpu.reg.clone();
    let mut next_state = last_state;

    verbose_println!("\n\n    Begin execution...\n");
    match args.step_by {
        Some(step_size) => loop {
            for _ in 0..step_size {
                cycle_num += 1;
                if args.cycle_count {
                    print_cycles(&cycle_num);
                }
                run_cycle(
                    &mut cpu,
                    &mut next_state,
                    &mut last_state,
                    &mut instructions_seen,
                );
            }
            print!(
                "                       ...{} cycles - press enter to continue\r",
                cycle_num
            );
            stdout().flush().unwrap();
            pause_once();
        },
        None => loop {
            cycle_num += 1;
            if args.cycle_count {
                print_cycles(&cycle_num);
            }
            run_cycle(
                &mut cpu,
                &mut next_state,
                &mut last_state,
                &mut instructions_seen,
            );
        },
    }
}

fn run_cycle(
    cpu: &mut CPU,
    next_state: &mut Registers,
    last_state: &mut Registers,
    instructions_seen: &mut Vec<u8>,
) {
    let will_pause;
    unsafe {
        will_pause = PAUSE_QUEUED.clone();
    }
    cpu.exec_next();
    unsafe {
        *next_state = cpu.reg;
        if !PAUSE_ENABLED {
            if next_state.pc >= 0x100 {
                PAUSE_ENABLED = true;
            }
        }
        *last_state = *next_state;
        if will_pause {
            pause();
        }
    }
    match instructions_seen.contains(&cpu.last_instruction) {
        true => {}
        false => {
            // println!("new instruction enountered: {:#X}", cpu.last_instruction);
            instructions_seen.push(cpu.last_instruction);
        }
    }
}

fn pause() {
    unsafe {
        if PAUSE_ENABLED {
            let line = &mut String::new();
            io::stdin().read_line(line).unwrap();
            PAUSE_QUEUED = !line.contains("continue");
        }
    }
}

fn pause_once() {
    io::stdin().read_line(&mut String::new()).unwrap();
}

fn print_cycles(cycles: &i32) {
    if *cycles % 45678 != 0 {
        return;
    }
    let instructions_per_second = 400000;
    print!(
        "cycle {} - approx {} seconds on real hardware\r",
        cycles,
        cycles / instructions_per_second
    );
    stdout().flush().unwrap();
}

fn is_verbose() -> bool {
    match VERBOSE.read() {
        Ok(v) => *v,
        Err(_) => false,
    }
}