feat(snd): simplify audio buffer

The audio buffer now is held by crossbeam. The developers of said
library could write a batter queue than I could anyday

src/bus.rs

@@ -70,6 +70,10 @@ impl Bus {
         self.snd.set_audio_src(sender)
     }
 
+    pub(crate) fn is_mpsc_still_full(&mut self) -> bool {
+        self.snd.is_mpsc_still_full()
+    }
+
     pub(crate) fn clock(&mut self) {
         self.ppu.clock();
         self.timer.clock();

src/cartridge.rs

@@ -183,7 +183,7 @@ impl Mbc1 {
         }
     }
 
-    fn mbcm_zero_bank(&self) -> u8 {
+    fn _mbcm_zero_bank(&self) -> u8 {
         use BankCount::*;
 
         match self.bank_count {

src/cpu.rs

@@ -126,8 +126,13 @@ impl Cpu {
         };
 
         let pending: u32 = cycles.into();
-        for _ in 0..pending {
-            self.bus.clock();
+        let mut offset = 0;
+        for _ in 0..(pending + offset) {
+            if !self.bus.is_mpsc_still_full() {
+                self.bus.clock();
+            } else {
+                offset += 1;
+            }
         }
 
         self.handle_interrupts();

src/emu.rs

@@ -11,6 +11,7 @@ pub const SM83_CYCLE_TIME: Duration = Duration::from_nanos(1_000_000_000 / SM83_
 pub const CYCLES_IN_FRAME: Cycle = Cycle::new(456 * 154); // 456 Cycles times 154 scanlines
 pub(crate) const SM83_CLOCK_SPEED: u64 = 0x40_0000; // Hz which is 4.194304Mhz
 const DEFAULT_TITLE: &str = "DMG-01 Emulator";
+const GAMEPAD_ENABLED: bool = false;
 
 pub fn init(boot_path: Option<&str>, rom_path: &str) -> Result<SM83> {
     let mut cpu = match boot_path {
@@ -44,12 +45,13 @@ pub fn run(
 }
 
 pub fn run_unsynced(game_boy: &mut SM83, gamepad: &mut Gilrs, input: &WinitInputHelper) -> Cycle {
-    if let Some(event) = gamepad.next_event() {
-        joypad::handle_gamepad_input(game_boy.joypad_mut(), event);
-    } else {
-        joypad::handle_keyboard_input(game_boy.joypad_mut(), input);
+    if GAMEPAD_ENABLED {
+        if let Some(event) = gamepad.next_event() {
+            joypad::handle_gamepad_input(game_boy.joypad_mut(), event);
+        }
     }
 
+    joypad::handle_keyboard_input(game_boy.joypad_mut(), input);
     game_boy.step()
 }
 

src/sound.rs

@@ -1,14 +1,17 @@
 use bitfield::bitfield;
-use crossbeam_channel::{Receiver, Sender};
+use crossbeam_channel::{Receiver, Sender, TrySendError};
 use rodio::Source;
 
 use crate::emu::SM83_CLOCK_SPEED;
 
 const WAVE_PATTERN_RAM_LEN: usize = 0x10;
+
 const SAMPLE_RATE: u32 = 48000; // Hz
+const AUDIO_BUFFER_LEN: usize = 1024;
+const CHANNEL_COUNT: u16 = 2;
 const SAMPLE_INCREMENT: u64 = SAMPLE_RATE as u64;
 
-#[derive(Debug, Clone, Default)]
+#[derive(Default, Debug, Clone)]
 pub(crate) struct Sound {
     pub(crate) ctrl: SoundControl,
     /// Tone & Sweep
@@ -26,6 +29,8 @@ pub(crate) struct Sound {
 
     sender: Option<SampleSender>,
     sample_counter: u64,
+
+    is_mpsc_full: bool,
 }
 
 impl Sound {
@@ -85,11 +90,16 @@ impl Sound {
             let ch4_left = self.ctrl.output.ch4_left() as u8 as f32 * ch4_amplitude;
             let ch4_right = self.ctrl.output.ch4_right() as u8 as f32 * ch4_amplitude;
 
-            let left_sample = (ch1_left + ch2_left + ch3_left + ch4_left) / 4.0;
-            let right_sample = (ch1_right + ch2_right + ch3_right + ch4_right) / 4.0;
+            let left = (ch1_left + ch2_left + ch3_left + ch4_left) / 4.0;
+            let right = (ch1_right + ch2_right + ch3_right + ch4_right) / 4.0;
 
-            if let Some(send) = self.sender.as_ref() {
-                send.add_sample(left_sample, right_sample);
+            if let Some(s) = self.sender.as_ref() {
+                let _ = s.send_samples(left, right).map_err(|e| match e {
+                    TrySendError::Full(_) => self.is_mpsc_full = true,
+                    TrySendError::Disconnected(_) => {
+                        panic!("Audio Sample MPSC Channel Disconnected")
+                    }
+                });
             }
         }
     }
@@ -98,6 +108,14 @@ impl Sound {
         self.sender = Some(sender);
     }
 
+    pub(crate) fn is_mpsc_still_full(&mut self) -> bool {
+        if let Some(sender) = self.sender.as_ref() {
+            self.is_mpsc_full = sender.is_full();
+        }
+
+        self.is_mpsc_full
+    }
+
     fn clock_length(freq_hi: &FrequencyHigh, length_timer: &mut u16, enabled: &mut bool) {
         if freq_hi.idk() && *length_timer > 0 {
             *length_timer -= 1;
@@ -1158,31 +1176,30 @@ pub struct AudioSenderReceiver;
 
 impl AudioSenderReceiver {
     pub fn new() -> (SampleSender, SampleReceiver) {
-        let (send, recv) = crossbeam_channel::unbounded();
+        let (send, recv) = crossbeam_channel::bounded(AUDIO_BUFFER_LEN * 2);
 
-        (SampleSender { send }, SampleReceiver { recv })
+        (SampleSender { inner: send }, SampleReceiver { inner: recv })
     }
 }
 
 #[derive(Debug, Clone)]
 pub struct SampleSender {
-    send: Sender<f32>,
+    inner: Sender<f32>,
 }
 
 impl SampleSender {
-    fn add_sample(&self, left: f32, right: f32) {
-        self.send
-            .send(left)
-            .expect("Send audio sample across threads");
+    fn send_samples(&self, left: f32, right: f32) -> Result<(), TrySendError<f32>> {
+        self.inner.try_send(left).and(self.inner.try_send(right))?;
+        Ok(())
+    }
 
-        self.send
-            .send(right)
-            .expect("Send audio sample across threads");
+    fn is_full(&self) -> bool {
+        self.inner.is_full()
     }
 }
 
 pub struct SampleReceiver {
-    recv: Receiver<f32>,
+    inner: Receiver<f32>,
 }
 
 impl Iterator for SampleReceiver {
@@ -1190,7 +1207,7 @@ impl Iterator for SampleReceiver {
 
     fn next(&mut self) -> Option<Self::Item> {
         // TODO: Should this never return none?
-        self.recv.recv().ok()
+        self.inner.recv().ok()
     }
 }
 
@@ -1204,7 +1221,7 @@ impl Source for SampleReceiver {
 
     fn channels(&self) -> u16 {
         // The Gameboy supports two channels
-        2
+        CHANNEL_COUNT
     }
 
     fn sample_rate(&self) -> u32 {