chore(apu): improve code organization

Reintroduce the Frame Sequencer and it's state enum (needed so that we
can reset the FS on NR52 enable)

src/apu.rs

@@ -5,6 +5,7 @@ use types::ch1::{Sweep, SweepDirection};
 use types::ch3::Volume as Ch3Volume;
 use types::ch4::{CounterWidth, Frequency as Ch4Frequency, PolynomialCounter};
 use types::common::{EnvelopeDirection, FrequencyHigh, SoundDuty, VolumeEnvelope};
+use types::fs::{FrameSequencer, State as FrameSequencerState};
 use types::{ChannelControl, SoundOutput};
 
 pub mod gen;
@@ -25,7 +26,7 @@ pub struct Apu {
     /// Noise
     ch4: Channel4,
 
-    // Frame Sequencer
+    sequencer: FrameSequencer,
     div_prev: Option<u16>,
 
     prod: Option<SampleProducer<f32>>,
@@ -42,7 +43,7 @@ impl BusIo for Apu {
             0x16 => self.ch2.duty(),
             0x17 => self.ch2.envelope(),
             0x19 => self.ch2.freq_hi(),
-            0x1A => self.ch3.enabled(),
+            0x1A => self.ch3.dac_enabled(),
             0x1C => self.ch3.volume(),
             0x1E => self.ch3.freq_hi(),
             0x21 => self.ch4.envelope(),
@@ -70,7 +71,7 @@ impl BusIo for Apu {
             0x17 if self.ctrl.enabled => self.ch2.set_envelope(byte),
             0x18 if self.ctrl.enabled => self.ch2.set_freq_lo(byte),
             0x19 if self.ctrl.enabled => self.ch2.set_freq_hi(byte),
-            0x1A if self.ctrl.enabled => self.ch3.set_enabled(byte),
+            0x1A if self.ctrl.enabled => self.ch3.set_dac_enabled(byte),
             0x1B if self.ctrl.enabled => self.ch3.set_len(byte),
             0x1C if self.ctrl.enabled => self.ch3.set_volume(byte),
             0x1D if self.ctrl.enabled => self.ch3.set_freq_lo(byte),
@@ -96,33 +97,35 @@ impl Apu {
     pub(crate) fn tick(&mut self, div: u16) {
         self.sample_counter += SAMPLE_INCREMENT;
 
-        // Length Control (256Hz)
+        // Frame Sequencer (512Hz)
-        if self.falling_edge(13, div) {
+        if self.is_falling_edge(12, div) {
-            self.handle_length();
+            use FrameSequencerState::*;
+
+            match self.sequencer.state() {
+                Length => self.clock_length(),
+                LengthAndSweep => {
+                    self.clock_length();
+                    self.clock_sweep();
+                }
+                Envelope => self.clock_envelope(),
+                Nothing => {}
             }
 
-        // Sweep (128Hz)
+            self.sequencer.next();
-        if self.falling_edge(14, div) {
-            self.handle_sweep();
-        }
-
-        // Volume Envelope (64Hz)
-        if self.falling_edge(15, div) {
-            self.handle_volume();
         }
 
         self.div_prev = Some(div);
 
-        self.ch1.clock();
+        self.ch1.tick();
-        self.ch2.clock();
+        self.ch2.tick();
-        self.ch3.clock();
+        self.ch3.tick();
-        self.ch4.clock();
+        self.ch4.tick();
 
         if self.sample_counter >= SM83_CLOCK_SPEED {
             self.sample_counter %= SM83_CLOCK_SPEED;
 
             if let Some(ref mut prod) = self.prod {
-                if prod.available_block() {
+                if prod.available_blocking() {
                     // Sample the APU
                     let ch1_amplitude = self.ch1.amplitude();
                     let ch1_left = self.ctrl.output.ch1_left() as u8 as f32 * ch1_amplitude;
@@ -154,23 +157,20 @@ impl Apu {
         }
     }
 
-    pub fn set_producer(&mut self, prod: SampleProducer<f32>) {
-        self.prod = Some(prod);
-    }
-
     /// 0xFF26 | NR52 - Sound On/Off
     pub(crate) fn set_status(&mut self, byte: u8) {
         self.ctrl.enabled = (byte >> 7) & 0x01 == 0x01;
 
         if self.ctrl.enabled {
             // Frame Sequencer reset to Step 0
-            // TODO: With the current implementation of the frame sequencer, what does this even mean?
+            self.sequencer.reset();
 
             // Square Duty units are reset to first step
             self.ch1.duty_pos = 0;
             self.ch2.duty_pos = 0;
 
             // Wave Channel's sample buffer reset to 0
+            self.ch3.offset = 0;
         }
 
         if !self.ctrl.enabled {
@@ -179,6 +179,10 @@ impl Apu {
         }
     }
 
+    pub fn attach_producer(&mut self, prod: SampleProducer<f32>) {
+        self.prod = Some(prod);
+    }
+
     fn reset(&mut self) {
         self.ch1.sweep = Default::default();
         self.ch1.duty = Default::default();
@@ -191,7 +195,7 @@ impl Apu {
         self.ch2.freq_lo = Default::default();
         self.ch2.freq_hi = Default::default();
 
-        self.ch3.enabled = Default::default();
+        self.ch3.dac_enabled = Default::default();
         self.ch3.len = Default::default();
         self.ch3.volume = Default::default();
         self.ch3.freq_lo = Default::default();
@@ -205,13 +209,14 @@ impl Apu {
         self.ctrl.channel = Default::default();
         self.ctrl.output = Default::default();
 
-        // Disable the rest of the channels
+        // Disable the Channels
         self.ch1.enabled = Default::default();
         self.ch2.enabled = Default::default();
+        self.ch3.enabled = Default::default();
         self.ch4.enabled = Default::default();
     }
 
-    fn clock_length(freq_hi: &FrequencyHigh, length_timer: &mut u16, enabled: &mut bool) {
+    fn process_length(freq_hi: &FrequencyHigh, length_timer: &mut u16, enabled: &mut bool) {
         if freq_hi.length_disable() && *length_timer > 0 {
             *length_timer -= 1;
 
@@ -223,7 +228,7 @@ impl Apu {
         }
     }
 
-    fn clock_length_ch4(freq: &Ch4Frequency, length_timer: &mut u16, enabled: &mut bool) {
+    fn ch4_process_length(freq: &Ch4Frequency, length_timer: &mut u16, enabled: &mut bool) {
         if freq.length_disable() && *length_timer > 0 {
             *length_timer -= 1;
 
@@ -235,33 +240,33 @@ impl Apu {
         }
     }
 
-    fn handle_length(&mut self) {
+    fn clock_length(&mut self) {
-        Self::clock_length(
+        Self::process_length(
             &self.ch1.freq_hi,
             &mut self.ch1.length_timer,
             &mut self.ch1.enabled,
         );
 
-        Self::clock_length(
+        Self::process_length(
             &self.ch2.freq_hi,
             &mut self.ch2.length_timer,
             &mut self.ch2.enabled,
         );
 
-        Self::clock_length(
+        Self::process_length(
             &self.ch3.freq_hi,
             &mut self.ch3.length_timer,
             &mut self.ch3.enabled,
         );
 
-        Self::clock_length_ch4(
+        Self::ch4_process_length(
             &self.ch4.freq,
             &mut self.ch4.length_timer,
             &mut self.ch4.enabled,
         );
     }
 
-    fn handle_sweep(&mut self) {
+    fn clock_sweep(&mut self) {
         if self.ch1.sweep_timer != 0 {
             self.ch1.sweep_timer -= 1;
         }
@@ -283,7 +288,7 @@ impl Apu {
         }
     }
 
-    fn clock_envelope(envelope: &VolumeEnvelope, period_timer: &mut u8, current_volume: &mut u8) {
+    fn process_envelope(envelope: &VolumeEnvelope, period_timer: &mut u8, current_volume: &mut u8) {
         use EnvelopeDirection::*;
 
         if envelope.period() != 0 {
@@ -303,29 +308,29 @@ impl Apu {
         }
     }
 
-    fn handle_volume(&mut self) {
+    fn clock_envelope(&mut self) {
         // Channels 1, 2 and 4 have Volume Envelopes
 
-        Self::clock_envelope(
+        Self::process_envelope(
             &self.ch1.envelope,
             &mut self.ch1.period_timer,
             &mut self.ch1.current_volume,
         );
 
-        Self::clock_envelope(
+        Self::process_envelope(
             &self.ch2.envelope,
             &mut self.ch2.period_timer,
             &mut self.ch2.current_volume,
         );
 
-        Self::clock_envelope(
+        Self::process_envelope(
             &self.ch4.envelope,
             &mut self.ch4.period_timer,
             &mut self.ch4.current_volume,
         );
     }
 
-    fn falling_edge(&self, bit: u8, div: u16) -> bool {
+    fn is_falling_edge(&self, bit: u8, div: u16) -> bool {
         match self.div_prev {
             Some(p) => (p >> bit & 0x01) == 0x01 && (div >> bit & 0x01) == 0x00,
             None => false,
@@ -411,23 +416,6 @@ pub(crate) struct Channel1 {
 }
 
 impl Channel1 {
-    fn amplitude(&self) -> f32 {
-        let dac_input = self.duty.wave_pattern().amplitude(self.duty_pos) * self.current_volume;
-
-        (dac_input as f32 / 7.5) - 1.0
-    }
-
-    fn clock(&mut self) {
-        if self.freq_timer != 0 {
-            self.freq_timer -= 1;
-        }
-
-        if self.freq_timer == 0 {
-            self.freq_timer = (2048 - self.frequency()) * 4;
-            self.duty_pos = (self.duty_pos + 1) % 8;
-        }
-    }
-
     /// 0xFF10 | NR10 - Channel 1 Sweep Register
     pub(crate) fn sweep(&self) -> u8 {
         u8::from(self.sweep) | 0x80
@@ -456,7 +444,11 @@ impl Channel1 {
 
     /// 0xFF12 | NR12 - Channel 1 Volume Envelope
     pub(crate) fn set_envelope(&mut self, byte: u8) {
-        self.envelope = byte.into()
+        self.envelope = byte.into();
+
+        if !self.is_dac_enabled() {
+            self.enabled = false;
+        }
     }
 
     /// 0xFF13 | NR13 - Channel 1 Frequency low (lower 8 bits only)
@@ -498,9 +490,31 @@ impl Channel1 {
                 self.length_timer = 64;
             }
 
+            if self.is_dac_enabled() {
                 self.enabled = true;
             }
         }
+    }
+
+    fn tick(&mut self) {
+        if self.freq_timer != 0 {
+            self.freq_timer -= 1;
+        }
+
+        if self.freq_timer == 0 {
+            self.freq_timer = (2048 - self.frequency()) * 4;
+            self.duty_pos = (self.duty_pos + 1) % 8;
+        }
+    }
+
+    fn amplitude(&self) -> f32 {
+        if self.is_dac_enabled() && self.enabled {
+            let input = self.duty.wave_pattern().amplitude(self.duty_pos) * self.current_volume;
+            (input as f32 / 7.5) - 1.0
+        } else {
+            0.0
+        }
+    }
 
     fn calc_sweep_freq(&mut self) -> u16 {
         use SweepDirection::*;
@@ -529,6 +543,10 @@ impl Channel1 {
     fn frequency(&self) -> u16 {
         (self.freq_hi.freq_bits() as u16) << 8 | self.freq_lo as u16
     }
+
+    fn is_dac_enabled(&self) -> bool {
+        self.envelope.0 & 0xF8 != 0x00
+    }
 }
 
 #[derive(Debug, Default)]
@@ -556,23 +574,6 @@ pub(crate) struct Channel2 {
 }
 
 impl Channel2 {
-    fn amplitude(&self) -> f32 {
-        let dac_input = self.duty.wave_pattern().amplitude(self.duty_pos) * self.current_volume;
-
-        (dac_input as f32 / 7.5) - 1.0
-    }
-
-    fn clock(&mut self) {
-        if self.freq_timer != 0 {
-            self.freq_timer -= 1;
-        }
-
-        if self.freq_timer == 0 {
-            self.freq_timer = (2048 - self.frequency()) * 4;
-            self.duty_pos = (self.duty_pos + 1) % 8;
-        }
-    }
-
     /// 0xFF16 | NR21 - Channel 2 Sound length / Wave Pattern Duty
     pub(crate) fn duty(&self) -> u8 {
         u8::from(self.duty) | 0x3F
@@ -591,7 +592,11 @@ impl Channel2 {
 
     /// 0xFF17 | NR22 - Channel 2 Volume ENvelope
     pub(crate) fn set_envelope(&mut self, byte: u8) {
-        self.envelope = byte.into()
+        self.envelope = byte.into();
+
+        if !self.is_dac_enabled() {
+            self.enabled = false;
+        }
     }
 
     /// 0xFF18 | NR23 - Channel 2 Frequency low (lower 8 bits only)
@@ -618,19 +623,45 @@ impl Channel2 {
                 self.length_timer = 64;
             }
 
+            if self.is_dac_enabled() {
                 self.enabled = true;
             }
         }
+    }
+
+    fn amplitude(&self) -> f32 {
+        if self.is_dac_enabled() && self.enabled {
+            let input = self.duty.wave_pattern().amplitude(self.duty_pos) * self.current_volume;
+            (input as f32 / 7.5) - 1.0
+        } else {
+            0.0
+        }
+    }
+
+    fn tick(&mut self) {
+        if self.freq_timer != 0 {
+            self.freq_timer -= 1;
+        }
+
+        if self.freq_timer == 0 {
+            self.freq_timer = (2048 - self.frequency()) * 4;
+            self.duty_pos = (self.duty_pos + 1) % 8;
+        }
+    }
 
     fn frequency(&self) -> u16 {
         (self.freq_hi.freq_bits() as u16) << 8 | self.freq_lo as u16
     }
+
+    fn is_dac_enabled(&self) -> bool {
+        self.envelope.0 & 0xF8 != 0x00
+    }
 }
 
 #[derive(Debug, Default)]
 pub(crate) struct Channel3 {
     /// 0xFF1A | NR30 - Channel 3 Sound on/off
-    enabled: bool,
+    dac_enabled: bool,
     /// 0xFF1B | NR31 - Sound Length
     len: u8,
     /// 0xFF1C | NR32 - Channel 3 Volume
@@ -647,6 +678,8 @@ pub(crate) struct Channel3 {
 
     freq_timer: u16,
     offset: u8,
+
+    enabled: bool,
 }
 
 impl BusIo for Channel3 {
@@ -671,13 +704,17 @@ impl Channel3 {
     const WAVE_RAM_START_ADDR: u16 = 0xFF30;
 
     /// 0xFF1A | NR30 - Channel 3 Sound on/off
-    pub(crate) fn enabled(&self) -> u8 {
+    pub(crate) fn dac_enabled(&self) -> u8 {
-        ((self.enabled as u8) << 7) | 0x7F
+        ((self.dac_enabled as u8) << 7) | 0x7F
     }
 
     /// 0xFF1A | NR30 - Channel 3 Sound on/off
-    pub(crate) fn set_enabled(&mut self, byte: u8) {
+    pub(crate) fn set_dac_enabled(&mut self, byte: u8) {
-        self.enabled = (byte >> 7) & 0x01 == 0x01;
+        self.dac_enabled = (byte >> 7) & 0x01 == 0x01;
+
+        if !self.dac_enabled {
+            self.enabled = false;
+        }
     }
 
     /// 0xFF1B | NR31 - Sound Length
@@ -724,18 +761,13 @@ impl Channel3 {
                 self.length_timer = 256;
             }
 
+            if self.dac_enabled {
                 self.enabled = true;
             }
         }
-
-    fn amplitude(&self) -> f32 {
-        let dac_input =
-            (self.read_sample(self.offset) >> self.volume.shift_count()) * self.enabled as u8;
-
-        (dac_input as f32 / 7.5) - 1.0
     }
 
-    fn clock(&mut self) {
+    fn tick(&mut self) {
         if self.freq_timer != 0 {
             self.freq_timer -= 1;
         }
@@ -746,6 +778,15 @@ impl Channel3 {
         }
     }
 
+    fn amplitude(&self) -> f32 {
+        if self.dac_enabled && self.enabled {
+            let input = self.read_sample(self.offset) >> self.volume.shift_count();
+            (input as f32 / 7.5) - 1.0
+        } else {
+            0.0
+        }
+    }
+
     fn read_sample(&self, index: u8) -> u8 {
         let i = (index / 2) as usize;
 
@@ -803,7 +844,11 @@ impl Channel4 {
 
     /// 0xFF21 | NR42 - Channel 4 Volume Envelope
     pub(crate) fn set_envelope(&mut self, byte: u8) {
-        self.envelope = byte.into()
+        self.envelope = byte.into();
+
+        if !self.is_dac_enabled() {
+            self.enabled = false;
+        }
     }
 
     /// 0xFF22 | NR43 - Chanel 4 Polynomial Counter
@@ -838,17 +883,13 @@ impl Channel4 {
             // LFSR behaviour during trigger event
             self.lf_shift = 0x7FFF;
 
+            if self.is_dac_enabled() {
                 self.enabled = true;
             }
         }
-
-    fn amplitude(&self) -> f32 {
-        let dac_input = (!self.lf_shift & 0x01) as u8 * self.current_volume;
-
-        (dac_input as f32 / 7.5) - 1.0
     }
 
-    fn clock(&mut self) {
+    fn tick(&mut self) {
         if self.freq_timer != 0 {
             self.freq_timer -= 1;
         }
@@ -866,6 +907,19 @@ impl Channel4 {
         }
     }
 
+    fn amplitude(&self) -> f32 {
+        if self.is_dac_enabled() && self.enabled {
+            let input = (!self.lf_shift & 0x01) as u8 * self.current_volume;
+            (input as f32 / 7.5) - 1.0
+        } else {
+            0.0
+        }
+    }
+
+    fn is_dac_enabled(&self) -> bool {
+        self.envelope.0 & 0xF8 != 0x00
+    }
+
     fn divisor(code: u8) -> u8 {
         if code == 0 {
             return 8;

src/apu/gen.rs

@@ -48,7 +48,7 @@ impl<T> SampleProducer<T> {
         self.inner.slots() > 2
     }
 
-    pub(crate) fn available_block(&self) -> bool {
+    pub(crate) fn available_blocking(&self) -> bool {
         loop {
             if self.inner.slots() > 2 {
                 break true;

src/apu/types.rs

@@ -73,7 +73,7 @@ pub(crate) mod ch1 {
     }
 }
 
-pub(crate) mod ch3 {
+pub(super) mod ch3 {
     #[derive(Debug, Clone, Copy)]
     pub(crate) enum Volume {
         Mute = 0,
@@ -102,7 +102,7 @@ pub(crate) mod ch3 {
     }
 }
 
-pub(crate) mod ch4 {
+pub(super) mod ch4 {
     use super::bitfield;
 
     bitfield! {
@@ -217,7 +217,7 @@ pub(crate) mod ch4 {
     }
 }
 
-pub(crate) mod common {
+pub(super) mod common {
     use super::bitfield;
 
     bitfield! {
@@ -508,3 +508,52 @@ impl From<ChannelControl> for u8 {
         ctrl.0
     }
 }
+
+pub(super) mod fs {
+    #[derive(Debug)]
+    pub(crate) struct FrameSequencer {
+        step: u8,
+        state: State,
+    }
+
+    impl Default for FrameSequencer {
+        fn default() -> Self {
+            Self {
+                step: Default::default(),
+                state: State::Length,
+            }
+        }
+    }
+
+    impl FrameSequencer {
+        pub(crate) fn next(&mut self) {
+            use State::*;
+
+            self.step = (self.step + 1) % 8;
+            self.state = match self.step {
+                1 | 3 | 5 => Nothing,
+                0 | 4 => Length,
+                2 | 6 => LengthAndSweep,
+                7 => Envelope,
+                _ => unreachable!("Step {} is invalid for the Frame Sequencer", self.step),
+            };
+        }
+
+        pub(crate) fn state(&self) -> State {
+            self.state
+        }
+
+        pub(crate) fn reset(&mut self) {
+            self.step = Default::default();
+            self.state = State::Length;
+        }
+    }
+
+    #[derive(Debug, Clone, Copy)]
+    pub(crate) enum State {
+        Length,
+        Nothing,
+        LengthAndSweep,
+        Envelope,
+    }
+}

src/main.rs

@@ -63,16 +63,16 @@ fn main() -> Result<()> {
     };
 
     // Initialize Audio
-    // let spsc: AudioSPSC<f32> = Default::default();
+    let spsc: AudioSPSC<f32> = Default::default();
-    // let (prod, cons) = spsc.init();
+    let (prod, cons) = spsc.init();
-    // let (_stream, stream_handle) = OutputStream::try_default().expect("Initialized Audio");
+    let (_stream, stream_handle) = OutputStream::try_default().expect("Initialized Audio");
-    // let sink = Sink::try_new(&stream_handle)?;
+    let sink = Sink::try_new(&stream_handle)?;
-    // sink.append(cons);
+    sink.append(cons);
-    // game_boy.apu_mut().set_producer(prod);
+    game_boy.apu_mut().attach_producer(prod);
 
-    // std::thread::spawn(move || {
+    std::thread::spawn(move || {
-    //     sink.sleep_until_end();
+        sink.sleep_until_end();
-    // });
+    });
 
     let mut start = Instant::now();
     let frame_time = Duration::from_secs_f64(1.0 / 59.73); // 59.73 Hz on Host