Add really basic sound mixer that can play simple tunes

agb/examples/mixer_basic.rs

@@ -0,0 +1,20 @@
+#![no_std]
+#![no_main]
+
+extern crate agb;
+
+use agb::sound;
+
+const I_WILL_NOT_LET_YOU_LET_ME_DOWN: &'static [u8] =
+    include_bytes!("i-will-not-let-you-let-me-down.raw");
+
+#[no_mangle]
+pub fn main() -> ! {
+    let gba = agb::Gba::new();
+    let mixer = gba.mixer;
+    mixer.enable();
+
+    mixer.play_sound_starting_at(&I_WILL_NOT_LET_YOU_LET_ME_DOWN[0], 8000);
+
+    loop {}
+}

agb/src/lib.rs

@@ -51,6 +51,7 @@ static mut GBASINGLE: single::Singleton<Gba> = single::Singleton::new(unsafe { G
 pub struct Gba {
     pub display: display::Display,
     pub sound: sound::dmg::Sound,
+    pub mixer: sound::mixer::Mixer,
 }
 
 impl Gba {
@@ -62,6 +63,7 @@ impl Gba {
         Self {
             display: display::Display::new(),
             sound: sound::dmg::Sound::new(),
+            mixer: sound::mixer::Mixer::new(),
         }
     }
 }

agb/src/sound/mixer.rs

@@ -0,0 +1,65 @@
+use crate::memory_mapped::MemoryMapped;
+
+#[non_exhaustive]
+pub struct Mixer {}
+
+impl Mixer {
+    pub(crate) const unsafe fn new() -> Self {
+        Mixer {}
+    }
+
+    pub fn enable(&self) {
+        set_sound_control_register_for_mixer();
+    }
+
+    pub fn play_sound_starting_at(&self, sound_memory: *const u8, frequency: i32) {
+        set_timer_counter_for_frequency_and_enable(frequency);
+        enable_dma1_for_sound(sound_memory);
+    }
+}
+
+// Once we have proper DMA support, we should use that rather than hard coding these here too
+const DMA1_SOURCE_ADDR: MemoryMapped<u32> = unsafe { MemoryMapped::new(0x0400_00bc) };
+const DMA1_DEST_ADDR: MemoryMapped<u32> = unsafe { MemoryMapped::new(0x0400_00c0) };
+const _DMA1_WORD_COUNT: MemoryMapped<u16> = unsafe { MemoryMapped::new(0x0400_00c4) }; // sound ignores this for some reason
+const DMA1_CONTROL: MemoryMapped<u16> = unsafe { MemoryMapped::new(0x0400_00c6) };
+
+const FIFOA_DEST_ADDR: u32 = 0x0400_00a0;
+
+// Similarly for proper timer support
+const TIMER0_COUNTER: MemoryMapped<u16> = unsafe { MemoryMapped::new(0x0400_0100) };
+const TIMER0_CONTROL: MemoryMapped<u16> = unsafe { MemoryMapped::new(0x0400_0102) };
+
+const SOUND_CONTROL: MemoryMapped<u16> = unsafe { MemoryMapped::new(0x0400_0082) };
+const SOUND_CONTROL_X: MemoryMapped<u16> = unsafe { MemoryMapped::new(0x0400_0084) };
+
+fn enable_dma1_for_sound(sound_memory: *const u8) {
+    let dest_fixed: u16 = 2 << 5; // dest addr control = fixed
+    let repeat: u16 = 1 << 9;
+    let transfer_type: u16 = 1 << 10; // transfer in words
+    let dma_start_timing: u16 = 3 << 12; // sound fifo timing
+    let enable: u16 = 1 << 15; // enable
+
+    DMA1_SOURCE_ADDR.set(sound_memory as u32);
+    DMA1_DEST_ADDR.set(FIFOA_DEST_ADDR);
+    DMA1_CONTROL.set(dest_fixed | repeat | transfer_type | dma_start_timing | enable);
+}
+
+fn set_sound_control_register_for_mixer() {
+    let sound_a_volume_100: u16 = 1 << 2;
+    let sound_a_rout: u16 = 1 << 8;
+    let sound_a_lout: u16 = 1 << 9;
+    let sound_a_fifo_reset: u16 = 1 << 11;
+
+    SOUND_CONTROL.set(sound_a_volume_100 | sound_a_rout | sound_a_lout | sound_a_fifo_reset);
+
+    // master sound enable
+    SOUND_CONTROL_X.set(1 << 7);
+}
+
+fn set_timer_counter_for_frequency_and_enable(frequency: i32) {
+    let counter = 65536 - (16777216 / frequency);
+    TIMER0_COUNTER.set(counter as u16);
+
+    TIMER0_CONTROL.set(1 << 7); // enable the timer
+}

agb/src/sound/mod.rs

@@ -1 +1,2 @@
 pub mod dmg;
+pub mod mixer;