Merge pull request #123 from gwilymk/stereo-sound

Stereo sound

agb-sound-converter/src/lib.rs

@@ -66,9 +66,12 @@ pub fn include_wav(input: TokenStream) -> TokenStream {
 
     let result = quote! {
         {
+            #[repr(align(4))]
+            struct AlignmentWrapper<const N: usize>([u8; N]);
+
             const _: &[u8] = include_bytes!(#include_path);
 
-            include_bytes!(#out_file_path_include)
+            &AlignmentWrapper(*include_bytes!(#out_file_path_include)).0
         }
     };
 

agb/examples/stereo_sound.rs

@@ -0,0 +1,28 @@
+#![no_std]
+#![no_main]
+
+extern crate agb;
+
+use agb::sound::mixer::SoundChannel;
+use agb::{include_wav, 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");
+
+#[agb::entry]
+fn main() -> ! {
+    let mut gba = Gba::new();
+    let vblank_provider = agb::interrupt::VBlank::get();
+
+    let mut mixer = gba.mixer.mixer();
+    mixer.enable();
+
+    let mut channel = SoundChannel::new(LET_IT_IN);
+    channel.stereo();
+    mixer.play_sound(channel).unwrap();
+
+    loop {
+        vblank_provider.wait_for_vblank();
+        mixer.vblank();
+    }
+}

agb/src/sound/mixer/mixer.s

@@ -93,6 +93,60 @@ same_modification:
 
 agb_arm_end agb_rs__mixer_add
 
+agb_arm_func agb_rs__mixer_add_stereo
+    @ Arguments
+    @ r0 - pointer to the data to be copied (u8 array)
+    @ r1 - pointer to the sound buffer (i16 array which will alternate left and right channels, 32-bit aligned)
+    @
+    @ The sound buffer must be SOUND_BUFFER_SIZE * 2 in size = 176 * 2
+    push {r4-r8}
+
+    ldr r5, =0x00000FFF
+
+.macro mixer_add_loop_simple_stereo
+    ldrsh r6, [r0], #2        @ load the current sound sample to r6
+
+    ldr r4, [r1]             @ read the current value
+
+    @ This is slightly convoluted, but is mainly done for performance reasons. It is better
+    @ to hit ROM just once and then do 3 really simple instructions then do 2 ldrsbs however annoying
+    @ this is. Also, since all this code is in IWRAM and we never hit ROM otherwise, all accesses
+    @ are sequential and exactly the size of the bus to ROM (16 bits), so hopefully this will be super fast.
+    @
+    @ The next 3 instructions set up the current value in r6 to be in the expected format
+    @ 1 = 2s complement marks (so if negative, these are all 1s, if positive these are 0s)
+    @ L = the left sample
+    @ R = the right sample
+    @ 0 = all zeros
+    @ Split into bytes
+    @
+    @ At this point
+    @                        r6 = | 1 | 1 | L | R | where the upper bytes are 1s if L is negative. No care about R
+                         @ asr #8 | 1 | 1 | 1 | L | drop R off the right hand side
+    and r7, r5, r6, asr #8 @ r7 = | 0 | 0 | 1 | L | exactly what we want this to be. The mask puts the 1 as 00001111 ready for the shift later
+    lsl r6, r6, #24        @ r6 = | R | 0 | 0 | 0 | drop everything except the right sample
+    orr r6, r7, r6, asr #8 @ r6 = | 1 | R | 1 | L | now we have it perfectly set up
+
+    add r4, r4, r6, lsl #4  @ r4 += r6 << 4 (calculating both the left and right samples together)
+
+    str r4, [r1], #4         @ store the new value, and increment the pointer
+.endm
+
+    mov r8, #SOUND_BUFFER_SIZE
+1:
+    mixer_add_loop_simple_stereo
+    mixer_add_loop_simple_stereo
+    mixer_add_loop_simple_stereo
+    mixer_add_loop_simple_stereo
+
+    subs r8, r8, #4          @ loop counter
+    bne 1b                   @ jump back if we're done with the loop
+
+    pop {r4-r8}
+    bx lr
+
+agb_arm_end agb_rs__mixer_add_stereo
+
 .macro clamp_s8 reg:req
     cmn \reg, #127
     mvnlt \reg, #127

agb/src/sound/mixer/mod.rs

@@ -35,6 +35,8 @@ pub struct SoundChannel {
     panning: Num<i16, 4>, // between -1 and 1
     is_done: bool,
 
+    is_stereo: bool,
+
     priority: SoundPriority,
 }
 
@@ -49,6 +51,7 @@ impl SoundChannel {
             is_done: false,
             priority: SoundPriority::Low,
             volume: 1.into(),
+            is_stereo: false,
         }
     }
 
@@ -62,6 +65,7 @@ impl SoundChannel {
             is_done: false,
             priority: SoundPriority::High,
             volume: 1.into(),
+            is_stereo: false,
         }
     }
 
@@ -91,6 +95,12 @@ impl SoundChannel {
         self
     }
 
+    pub fn stereo(&mut self) -> &mut Self {
+        self.is_stereo = true;
+
+        self
+    }
+
     pub fn stop(&mut self) {
         self.is_done = true
     }

agb/src/sound/mixer/sw_mixer.rs

@@ -13,6 +13,8 @@ extern "C" {
         right_amount: Num<i16, 4>,
     );
 
+    fn agb_rs__mixer_add_stereo(sound_data: *const u8, sound_buffer: *mut Num<i16, 4>);
+
     fn agb_rs__mixer_collapse(sound_buffer: *mut i8, input_buffer: *const Num<i16, 4>);
 }
 
@@ -133,12 +135,16 @@ impl MixerBuffer {
                 continue;
             }
 
+            let playback_speed = if channel.is_stereo {
+                2.into()
+            } else {
+                channel.playback_speed
+            };
+
             let right_amount = ((channel.panning + 1) / 2) * channel.volume;
             let left_amount = ((-channel.panning + 1) / 2) * channel.volume;
 
-            if (channel.pos + channel.playback_speed * SOUND_BUFFER_SIZE).floor()
-                >= channel.data.len()
-            {
+            if (channel.pos + playback_speed * SOUND_BUFFER_SIZE).floor() >= channel.data.len() {
                 // TODO: This should probably play what's left rather than skip the last bit
                 if channel.should_loop {
                     channel.pos -= channel.data.len();
@@ -148,16 +154,26 @@ impl MixerBuffer {
                 }
             }
 
+            if channel.is_stereo {
+                unsafe {
+                    agb_rs__mixer_add_stereo(
+                        channel.data.as_ptr().add(channel.pos.floor()),
+                        buffer.as_mut_ptr(),
+                    );
+                }
+            } else {
                 unsafe {
                     agb_rs__mixer_add(
                         channel.data.as_ptr().add(channel.pos.floor()),
                         buffer.as_mut_ptr(),
-                    channel.playback_speed,
+                        playback_speed,
                         left_amount,
                         right_amount,
                     );
                 }
-            channel.pos += channel.playback_speed * SOUND_BUFFER_SIZE;
+            }
+
+            channel.pos += playback_speed * SOUND_BUFFER_SIZE;
         }
 
         let write_buffer = self.get_write_buffer();