Add simple double buffer

agb/src/sound/mixer.rs

@@ -1,20 +1,24 @@
 use crate::memory_mapped::MemoryMapped;
 
 #[non_exhaustive]
-pub struct Mixer {}
+pub struct Mixer {
+    buffer: MixerBuffer,
+}
 
 impl Mixer {
     pub(crate) const unsafe fn new() -> Self {
-        Mixer {}
+        Mixer {
+            buffer: MixerBuffer::new(),
+        }
     }
 
     pub fn enable(&self) {
         set_sound_control_register_for_mixer();
+        set_timer_counter_for_frequency_and_enable(SOUND_FREQUENCY);
     }
 
-    pub fn play_sound_starting_at(&self, sound_memory: &[u8]) {
-        set_timer_counter_for_frequency_and_enable(SOUND_FREQUENCY);
-        enable_dma1_for_sound(sound_memory);
+    pub fn vblank(&mut self) {
+        self.buffer.swap();
     }
 }
 
@@ -23,6 +27,34 @@ impl Mixer {
 const SOUND_FREQUENCY: i32 = 10512;
 const SOUND_BUFFER_SIZE: usize = 176;
 
+struct MixerBuffer {
+    buffer1: [i8; SOUND_BUFFER_SIZE],
+    buffer2: [i8; SOUND_BUFFER_SIZE],
+
+    buffer_1_active: bool,
+}
+
+impl MixerBuffer {
+    fn new() -> Self {
+        MixerBuffer {
+            buffer1: Default::default(),
+            buffer2: Default::default(),
+
+            buffer_1_active: true,
+        }
+    }
+
+    fn swap(&mut self) {
+        if self.buffer_1_active {
+            enable_dma1_for_sound(&self.buffer1);
+        } else {
+            enable_dma1_for_sound(&self.buffer2);
+        }
+
+        self.buffer_1_active = !self.buffer_1_active;
+    }
+}
+
 // 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) };
@@ -38,14 +70,14 @@ 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: &[u8]) {
+fn enable_dma1_for_sound(sound_memory: &[i8]) {
     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
 
-    let address: *const u8 = &sound_memory[0];
+    let address: *const i8 = &sound_memory[0];
     DMA1_SOURCE_ADDR.set(address as u32);
     DMA1_DEST_ADDR.set(FIFOA_DEST_ADDR);
     DMA1_CONTROL.set(dest_fixed | repeat | transfer_type | dma_start_timing | enable);