From fd610d8cc1accb7c59984b731845cdddea8d8e80 Mon Sep 17 00:00:00 2001
From: Gwilym Kuiper <gw@ilym.me>
Date: Thu, 18 Nov 2021 22:06:57 +0000
Subject: [PATCH] Add support for timers

---
 agb/examples/stereo_sound.rs |  31 ++++++++++-
 agb/src/lib.rs               |   4 ++
 agb/src/timer.rs             | 105 +++++++++++++++++++++++++++++++++++
 3 files changed, 139 insertions(+), 1 deletion(-)
 create mode 100644 agb/src/timer.rs

diff --git a/agb/examples/stereo_sound.rs b/agb/examples/stereo_sound.rs
index b7dca810..b300029f 100644
--- a/agb/examples/stereo_sound.rs
+++ b/agb/examples/stereo_sound.rs
@@ -4,7 +4,7 @@
 extern crate agb;
 
 use agb::sound::mixer::SoundChannel;
-use agb::{include_wav, Gba};
+use agb::{include_wav, timer::Timer, Gba};
 
 // Music - "Let it in" by Josh Woodward, free download at http://joshwoodward.com
 const LET_IT_IN: &[u8] = include_wav!("examples/JoshWoodward-LetItIn.wav");
@@ -14,6 +14,12 @@ fn main() -> ! {
     let mut gba = Gba::new();
     let vblank_provider = agb::interrupt::VBlank::get();
 
+    let mut timer_controller = gba.timer;
+    timer_controller.set_overflow_amount(Timer::Timer1, u16::MAX);
+    timer_controller.set_enabled(Timer::Timer1, true);
+    timer_controller.set_overflow_amount(Timer::Timer2, u16::MAX);
+    timer_controller.set_cascade(Timer::Timer2, true);
+
     let mut mixer = gba.mixer.mixer();
     mixer.enable();
 
@@ -21,8 +27,31 @@ fn main() -> ! {
     channel.stereo();
     mixer.play_sound(channel).unwrap();
 
+    let mut frame_counter = 0i32;
     loop {
         vblank_provider.wait_for_vblank();
+        let before_mixing_cycles_lo = timer_controller.get_value(Timer::Timer1);
+        let before_mixing_cycles_hi = timer_controller.get_value(Timer::Timer2);
         mixer.vblank();
+        let after_mixing_cycles_lo = timer_controller.get_value(Timer::Timer1);
+        let after_mixing_cycles_hi = timer_controller.get_value(Timer::Timer2);
+
+        frame_counter = frame_counter.wrapping_add(1);
+
+        if frame_counter % 128 == 0 {
+            let before_mixing_cycles =
+                ((before_mixing_cycles_hi as u32) << 16) | before_mixing_cycles_lo as u32;
+            let after_mixing_cycles =
+                ((after_mixing_cycles_hi as u32) << 16) | after_mixing_cycles_lo as u32;
+
+            let total_cycles = after_mixing_cycles.wrapping_sub(before_mixing_cycles);
+
+            let percent = (total_cycles * 100) / 280896;
+            agb::println!(
+                "Took {} cycles to calculate mixer ~= {}% of total frame",
+                total_cycles,
+                percent
+            );
+        }
     }
 }
diff --git a/agb/src/lib.rs b/agb/src/lib.rs
index 4dc39172..a3831b2e 100644
--- a/agb/src/lib.rs
+++ b/agb/src/lib.rs
@@ -39,6 +39,8 @@ mod single;
 pub mod sound;
 /// System BIOS calls / syscalls.
 pub mod syscall;
+/// Interactions with the internal timers
+pub mod timer;
 
 #[cfg(not(test))]
 use core::fmt::Write;
@@ -61,6 +63,7 @@ pub struct Gba {
     pub display: display::Display,
     pub sound: sound::dmg::Sound,
     pub mixer: sound::mixer::MixerController,
+    pub timer: timer::TimerController,
 }
 
 impl Gba {
@@ -73,6 +76,7 @@ impl Gba {
             display: display::Display::new(),
             sound: sound::dmg::Sound::new(),
             mixer: sound::mixer::MixerController::new(),
+            timer: timer::TimerController::new(),
         }
     }
 }
diff --git a/agb/src/timer.rs b/agb/src/timer.rs
new file mode 100644
index 00000000..26f820d4
--- /dev/null
+++ b/agb/src/timer.rs
@@ -0,0 +1,105 @@
+use crate::memory_mapped::MemoryMapped;
+
+const fn timer_data(timer: usize) -> MemoryMapped<u16> {
+    unsafe { MemoryMapped::new(0x0400_0100 + 4 * timer) }
+}
+
+const fn timer_control(timer: usize) -> MemoryMapped<u16> {
+    unsafe { MemoryMapped::new(0x0400_0102 + 4 * timer) }
+}
+
+#[derive(Clone, Copy)]
+pub enum Timer {
+    Timer0,
+    Timer1,
+    Timer2,
+    Timer3,
+}
+
+#[derive(Clone, Copy)]
+pub enum Divider {
+    // 16.78MHz or 59.59ns
+    Divider1,
+    // 262.21kHz or 3.815us
+    Divider64,
+    // 65.536kHz or 15.26us
+    Divider256,
+    // 16.384kHz or 61.04us
+    Divider1024,
+}
+
+impl Divider {
+    fn get_as_bits(&self) -> u16 {
+        use Divider::*;
+
+        match self {
+            Divider1 => 0,
+            Divider64 => 1,
+            Divider256 => 2,
+            Divider1024 => 3,
+        }
+    }
+}
+
+#[non_exhaustive]
+pub struct TimerController {}
+
+impl TimerController {
+    pub(crate) const unsafe fn new() -> Self {
+        Self {}
+    }
+
+    pub fn set_overflow_amount(&mut self, timer: Timer, n: u16) {
+        timer.set_overflow_amount(n);
+    }
+
+    pub fn get_value(&mut self, timer: Timer) -> u16 {
+        timer.get_value()
+    }
+
+    pub fn set_divider(&mut self, timer: Timer, divider: Divider) {
+        timer
+            .control_register()
+            .set_bits(divider.get_as_bits(), 2, 0);
+    }
+
+    pub fn set_enabled(&mut self, timer: Timer, enabled: bool) {
+        let bit = if enabled { 1 } else { 0 };
+        timer.control_register().set_bits(bit, 1, 7);
+    }
+
+    pub fn set_cascade(&mut self, timer: Timer, cascade: bool) {
+        let bit = if cascade { 1 } else { 0 };
+        timer.control_register().set_bits(bit, 1, 2);
+    }
+}
+
+impl Timer {
+    fn set_overflow_amount(&self, n: u16) {
+        let count_up_value = 0u16.wrapping_sub(n);
+        self.data_register().set(count_up_value);
+    }
+
+    fn get_value(&self) -> u16 {
+        self.data_register().get()
+    }
+
+    fn data_register(&self) -> MemoryMapped<u16> {
+        timer_data(self.get_timer_number())
+    }
+
+    fn control_register(&self) -> MemoryMapped<u16> {
+        timer_control(self.get_timer_number())
+    }
+
+    fn get_timer_number(&self) -> usize {
+        use Timer::*;
+
+        match self {
+            Timer0 => 0,
+            Timer1 => 1,
+            Timer2 => 2,
+            Timer3 => 3,
+        }
+    }
+}