feat: implement ch1

TODO: It's really loud

src/apu.zig

@@ -24,7 +24,8 @@ pub const Apu = struct {
     chB: DmaSound(.B),
 
     bias: io.SoundBias,
-    ch_vol_cnt: io.ChannelVolumeControl,
+    /// NR51
+    psg_cnt: io.ChannelVolumeControl,
     dma_cnt: io.DmaSoundControl,
     cnt: io.SoundControl,
 
@@ -32,16 +33,19 @@ pub const Apu = struct {
     stream: *SDL.SDL_AudioStream,
     sched: *Scheduler,
 
+    fs: FrameSequencer,
+    capacitor: f32,
+
     pub fn init(sched: *Scheduler) Self {
         const apu: Self = .{
-            .ch1 = ToneSweep.init(),
+            .ch1 = ToneSweep.init(sched),
             .ch2 = Tone.init(),
             .ch3 = Wave.init(),
             .ch4 = Noise.init(),
             .chA = DmaSound(.A).init(),
             .chB = DmaSound(.B).init(),
 
-            .ch_vol_cnt = .{ .raw = 0 },
+            .psg_cnt = .{ .raw = 0 },
             .dma_cnt = .{ .raw = 0 },
             .cnt = .{ .raw = 0 },
             .bias = .{ .raw = 0x0200 },
@@ -49,13 +53,23 @@ pub const Apu = struct {
             .sampling_cycle = 0b00,
             .stream = SDL.SDL_NewAudioStream(SDL.AUDIO_F32, 2, 1 << 15, SDL.AUDIO_F32, 2, host_sample_rate) orelse unreachable,
             .sched = sched,
+
+            .capacitor = 0,
+            .fs = FrameSequencer.init(),
         };
 
         sched.push(.SampleAudio, sched.now() + apu.sampleTicks());
+        sched.push(.{ .ApuChannel = 0 }, sched.now() + SquareWave.ticks);
+        sched.push(.FrameSequencer, sched.now() + ((1 << 24) / 512));
 
         return apu;
     }
 
+    fn reset(self: *Self) void {
+        self.ch1.reset();
+        // TODO: Reset the rest of the channels
+    }
+
     pub fn setDmaCnt(self: *Self, value: u16) void {
         const new: io.DmaSoundControl = .{ .raw = value };
 
@@ -67,16 +81,42 @@ pub const Apu = struct {
         self.dma_cnt = new;
     }
 
+    /// NR52
     pub fn setSoundCntX(self: *Self, value: bool) void {
         self.cnt.apu_enable.write(value);
+
+        if (value) {
+            self.fs.step = 0; // Reset Frame Sequencer
+
+            // TODO: Reset Duty Position for Ch2 Square
+            self.ch1.square.pos = 0;
+
+            // TODO: Reset Channel 3 offset ptr
+        } else {
+            self.reset();
+        }
     }
 
+    /// NR52
+    pub fn soundCntX(self: *const Self) u32 {
+        const apu_enable = @boolToInt(self.cnt.apu_enable.read());
+
+        const ch1_enable = @boolToInt(self.ch1.enabled);
+        const ch2_enable = @boolToInt(self.ch2.enabled);
+        const ch3_enable = @boolToInt(self.ch3.enabled);
+        const ch4_enable = @boolToInt(self.ch4.enabled);
+
+        return apu_enable << 7 | ch4_enable << 3 | ch3_enable << 2 | ch2_enable << 1 | ch1_enable;
+    }
+
+    /// NR50
     pub fn setSoundCntLLow(self: *Self, byte: u8) void {
-        self.ch_vol_cnt.raw = (self.ch_vol_cnt.raw & 0xFF00) | byte;
+        self.psg_cnt.raw = (self.psg_cnt.raw & 0xFF00) | byte;
     }
 
+    /// NR51
     pub fn setSoundCntLHigh(self: *Self, byte: u8) void {
-        self.ch_vol_cnt.raw = @as(u16, byte) << 8 | (self.ch_vol_cnt.raw & 0xFF);
+        self.psg_cnt.raw = @as(u16, byte) << 8 | (self.psg_cnt.raw & 0xFF);
     }
 
     pub fn setBiasHigh(self: *Self, byte: u8) void {
@@ -84,16 +124,48 @@ pub const Apu = struct {
     }
 
     pub fn sampleAudio(self: *Self, late: u64) void {
-        const chA = if (self.dma_cnt.chA_vol.read()) self.chA.amplitude() else self.chA.amplitude() / 2;
-        const chA_left = if (self.dma_cnt.chA_left.read()) chA else 0;
-        const chA_right = if (self.dma_cnt.chA_right.read()) chA else 0;
 
-        const chB = if (self.dma_cnt.chB_vol.read()) self.chB.amplitude() else self.chB.amplitude() / 2;
-        const chB_left = if (self.dma_cnt.chB_left.read()) chB else 0;
-        const chB_right = if (self.dma_cnt.chB_right.read()) chB else 0;
+        // Sample Channel 1
+        const ch1_sample = self.highPassFilter(self.ch1.amplitude(), self.ch1.enabled);
+        const ch1_left = if (self.psg_cnt.ch1_left.read()) ch1_sample else 0;
+        const ch1_right = if (self.psg_cnt.ch1_right.read()) ch1_sample else 0;
 
-        const left = (chA_left + chB_left) / 2;
-        const right = (chA_right + chB_right) / 2;
+        const mixed_left = ch1_left;
+        const mixed_right = ch1_right;
+
+        // Apply NR50 Volume Modifications
+        const nr50_left = (@intToFloat(f32, self.psg_cnt.left_vol.read()) + 1.0) * mixed_left;
+        const nr50_right = (@intToFloat(f32, self.psg_cnt.right_vol.read()) + 1.0) * mixed_right;
+
+        // Apply SOUNDCNT_H Volume Modifications
+        const psg_left = switch (self.dma_cnt.ch_vol.read()) {
+            0b00 => nr50_left * 0.25,
+            0b01 => nr50_left * 0.5,
+            0b10 => nr50_left * 0.75,
+            0b11 => nr50_left, // Prohibited
+        };
+
+        const psg_right = switch (self.dma_cnt.ch_vol.read()) {
+            0b00 => nr50_right * 0.25,
+            0b01 => nr50_right * 0.5,
+            0b10 => nr50_right * 0.75,
+            0b11 => nr50_right, // Prohibited
+        };
+
+        // Sample Dma Channels
+        // const chA = if (self.dma_cnt.chA_vol.read()) self.chA.amplitude() else self.chA.amplitude() / 2;
+        // const chA_left = if (self.dma_cnt.chA_left.read()) chA else 0;
+        // const chA_right = if (self.dma_cnt.chA_right.read()) chA else 0;
+
+        // const chB = if (self.dma_cnt.chB_vol.read()) self.chB.amplitude() else self.chB.amplitude() / 2;
+        // const chB_left = if (self.dma_cnt.chB_left.read()) chB else 0;
+        // const chB_right = if (self.dma_cnt.chB_right.read()) chB else 0;
+
+        // Mix all Channels
+        // const left = (chA_left + chB_left + psg_left) / 3;
+        // const right = (chA_right + chB_right + psg_right) / 3
+        const left = psg_left;
+        const right = psg_right;
 
         if (self.sampling_cycle != self.bias.sampling_cycle.read()) {
             log.warn("Sampling Cycle changed from {} to {}", .{ self.sampling_cycle, self.bias.sampling_cycle.read() });
@@ -121,6 +193,36 @@ pub const Apu = struct {
         return @as(u64, 1) << (15 + @as(u6, self.bias.sampling_cycle.read()));
     }
 
+    pub fn tickFrameSequencer(self: *Self, late: u64) void {
+        self.fs.tick();
+
+        switch (self.fs.step) {
+            7 => self.tickEnvelopes(), // Clock Envelope
+            0, 4 => self.tickLengths(), // Clock Length
+            2, 6 => {
+                // Clock Length and Sweep
+                self.tickLengths();
+                self.ch1.tickSweep();
+            },
+            1, 3, 5 => {},
+        }
+
+        self.sched.push(.FrameSequencer, self.sched.now() + ((1 << 24) / 512) - late);
+    }
+
+    fn tickLengths(self: *Self) void {
+        self.ch1.tickLength();
+        self.ch2.tickLength();
+        self.ch3.tickLength();
+        self.ch4.tickLength();
+    }
+
+    fn tickEnvelopes(self: *Self) void {
+        self.ch1.tickEnvelope();
+        self.ch2.tickEnvelope();
+        self.ch4.tickEnvelope();
+    }
+
     pub fn handleTimerOverflow(self: *Self, cpu: *Arm7tdmi, tim_id: u3) void {
         if (!self.cnt.apu_enable.read()) return;
 
@@ -134,6 +236,18 @@ pub const Apu = struct {
             if (self.chB.len() <= 15) cpu.bus.dma._2.enableSoundDma(0x0400_00A4);
         }
     }
+
+    fn highPassFilter(self: *Self, sample: f32, ch_enabled: bool) f32 {
+        const charge_factor = 0.999958;
+
+        var output: f32 = 0;
+        if (ch_enabled) {
+            output = sample - self.capacitor;
+            self.capacitor = sample - output * std.math.pow(f32, charge_factor, @intToFloat(f32, (1 << 22) / self.sampleRate()));
+        }
+
+        return output;
+    }
 };
 
 const ToneSweep = struct {
@@ -148,21 +262,185 @@ const ToneSweep = struct {
     /// NR13, NR14
     freq: io.Frequency,
 
-    fn init() Self {
+    /// Length Functionality
+    len_dev: Length,
+    /// Sweep Functionality
+    sweep_dev: Sweep,
+    /// Envelope Functionality
+    env_dev: Envelope,
+    /// Frequency Timer Functionality
+    square: SquareWave,
+    enabled: bool,
+
+    sample: u8,
+
+    const Sweep = struct {
+        const This = @This();
+
+        timer: u8,
+        enabled: bool,
+        shadow: u11,
+
+        pub fn init() This {
+            return .{
+                .timer = 0,
+                .enabled = false,
+                .shadow = 0,
+            };
+        }
+
+        pub fn tick(this: *This, ch1: *Self) void {
+            if (this.timer != 0) this.timer -= 1;
+
+            if (this.timer == 0) {
+                const period = ch1.sweep.period.read();
+                this.timer = if (period == 0) 8 else period;
+
+                if (this.enabled and period != 0) {
+                    const new_freq = this.calcFrequency(ch1);
+
+                    if (new_freq <= 0x7FF and ch1.sweep.shift.read() != 0) {
+                        ch1.freq.frequency.write(@truncate(u11, new_freq));
+                        this.shadow = @truncate(u11, new_freq);
+
+                        _ = this.calcFrequency(ch1);
+                    }
+                }
+            }
+        }
+
+        fn calcFrequency(this: *This, ch1: *Self) u12 {
+            const shadow = @as(u12, this.shadow);
+            const shadow_shifted = shadow >> ch1.sweep.shift.read();
+            const decrease = ch1.sweep.direction.read();
+
+            const freq = if (decrease) shadow - shadow_shifted else shadow + shadow_shifted;
+
+            if (freq > 0x7FF) ch1.enabled = false;
+
+            return freq;
+        }
+    };
+
+    fn init(sched: *Scheduler) Self {
         return .{
             .sweep = .{ .raw = 0 },
             .duty = .{ .raw = 0 },
             .envelope = .{ .raw = 0 },
             .freq = .{ .raw = 0 },
+            .sample = 0,
+            .enabled = false,
+
+            .square = SquareWave.init(sched),
+            .len_dev = Length.init(),
+            .sweep_dev = Sweep.init(),
+            .env_dev = Envelope.init(),
         };
     }
 
+    fn reset(self: *Self) void {
+        self.sweep.raw = 0;
+        self.duty.raw = 0;
+        self.envelope.raw = 0;
+        self.freq.raw = 0;
+
+        self.sample = 0;
+        self.enabled = false;
+    }
+
+    fn tickSweep(self: *Self) void {
+        self.sweep_dev.tick(self);
+    }
+
+    pub fn tickLength(self: *Self) void {
+        self.len_dev.tick(self.freq, &self.enabled);
+    }
+
+    pub fn tickEnvelope(self: *Self) void {
+        self.env_dev.tick(self.envelope);
+    }
+
+    pub fn channelTimerOverflow(self: *Self, late: u64) void {
+        self.square.handleTimerOverflow(self.freq, late);
+
+        self.sample = 0;
+        if (!self.isDacEnabled()) return;
+        self.sample = if (self.enabled) self.square.sample(self.duty) * self.env_dev.vol else 0;
+    }
+
+    fn amplitude(self: *const Self) f32 {
+        return (@intToFloat(f32, self.sample) / 7.5) - 1.0;
+    }
+
+    /// NR11, NR12
+    pub fn setSoundCntH(self: *Self, value: u16) void {
+        self.setDuty(@truncate(u8, value));
+        self.setEnvelope(@truncate(u8, value >> 8));
+    }
+
+    /// NR11
+    pub fn setDuty(self: *Self, value: u8) void {
+        self.duty.raw = value;
+        self.len_dev.timer = @as(u7, self.duty.length.read() ^ 0x3F);
+    }
+
+    /// NR12
+    pub fn setEnvelope(self: *Self, value: u8) void {
+        self.envelope.raw = value;
+        if (!self.isDacEnabled()) self.enabled = false;
+    }
+
+    /// NR13, NR14
+    pub fn setFreq(self: *Self, fs: *const FrameSequencer, value: u16) void {
+        self.setFreqLow(@truncate(u8, value));
+        self.setFreqHigh(fs, @truncate(u8, value >> 8));
+    }
+
+    /// NR13
     pub fn setFreqLow(self: *Self, byte: u8) void {
         self.freq.raw = (self.freq.raw & 0xFF00) | byte;
     }
 
-    pub fn setFreqHigh(self: *Self, byte: u8) void {
-        self.freq.raw = (@as(u16, byte) << 8) | (self.freq.raw & 0xFF);
+    /// NR14
+    pub fn setFreqHigh(self: *Self, fs: *const FrameSequencer, byte: u8) void {
+        var new: io.Frequency = .{ .raw = (@as(u16, byte) << 8) | (self.freq.raw & 0xFF) };
+
+        if (new.trigger.read()) {
+            self.enabled = true; // FIXME: is this necessary?
+
+            if (self.len_dev.timer == 0) {
+                self.len_dev.timer = 64;
+
+                // We unset this on the old frequency because of the obscure
+                // behaviour outside of this if statement's scope
+                self.freq.length_enable.write(false);
+            }
+
+            // TODO: Reload Frequency Timer
+            self.square.reloadTimer(self.freq.frequency.read());
+
+            // Reload Envelope period and timer
+            self.env_dev.timer = self.envelope.period.read();
+            self.env_dev.vol = self.envelope.init_vol.read();
+
+            // Sweep Trigger Behaviour
+            const sw_period = self.sweep.period.read();
+            const sw_shift = self.sweep.shift.read();
+
+            self.sweep_dev.shadow = self.freq.frequency.read();
+            self.sweep_dev.timer = if (sw_period == 0) 8 else sw_period;
+            self.sweep_dev.enabled = sw_period != 0 or sw_shift != 0;
+            if (sw_shift != 0) _ = self.sweep_dev.calcFrequency(self);
+
+            self.enabled = self.isDacEnabled();
+        }
+
+        self.square.updateLength(fs, self, new);
+        self.freq = new;
+    }
+
+    fn isDacEnabled(self: *const Self) bool {
+        return self.envelope.raw & 0xF8 != 0;
     }
 };
 
@@ -176,14 +454,34 @@ const Tone = struct {
     /// NR23, NR24
     freq: io.Frequency,
 
+    /// Length Functionarlity
+    len_dev: Length,
+
+    /// Envelope Functionality
+    env_dev: Envelope,
+
+    enabled: bool,
+
     fn init() Self {
         return .{
             .duty = .{ .raw = 0 },
             .envelope = .{ .raw = 0 },
             .freq = .{ .raw = 0 },
+            .enabled = false,
+
+            .len_dev = Length.init(),
+            .env_dev = Envelope.init(),
         };
     }
 
+    pub fn tickLength(self: *Self) void {
+        self.len_dev.tick(self.freq, &self.enabled);
+    }
+
+    pub fn tickEnvelope(self: *Self) void {
+        self.env_dev.tick(self.envelope);
+    }
+
     pub fn setFreqLow(self: *Self, byte: u8) void {
         self.freq.raw = (self.freq.raw & 0xFF00) | byte;
     }
@@ -206,15 +504,27 @@ const Wave = struct {
     /// NR33, NR34
     freq: io.Frequency,
 
+    /// Length Functionarlity
+    len_dev: Length,
+
+    enabled: bool,
+
     fn init() Self {
         return .{
             .select = .{ .raw = 0 },
             .vol = .{ .raw = 0 },
             .freq = .{ .raw = 0 },
             .length = 0,
+
+            .len_dev = Length.init(),
+            .enabled = false,
         };
     }
 
+    pub fn tickLength(self: *Self) void {
+        self.len_dev.tick(self.freq, &self.enabled);
+    }
+
     pub fn setFreqLow(self: *Self, byte: u8) void {
         self.freq.raw = (self.freq.raw & 0xFF00) | byte;
     }
@@ -237,14 +547,34 @@ const Noise = struct {
     /// NR44
     cnt: io.NoiseControl,
 
+    /// Length Functionarlity
+    len_dev: Length,
+
+    /// Envelope Functionality
+    env_dev: Envelope,
+
+    enabled: bool,
+
     fn init() Self {
         return .{
             .len = 0,
             .envelope = .{ .raw = 0 },
             .poly = .{ .raw = 0 },
             .cnt = .{ .raw = 0 },
+            .enabled = false,
+
+            .len_dev = Length.init(),
+            .env_dev = Envelope.init(),
         };
     }
+
+    pub fn tickLength(self: *Self) void {
+        self.len_dev.ch4Tick(self.cnt, &self.enabled);
+    }
+
+    pub fn tickEnvelope(self: *Self) void {
+        self.env_dev.tick(self.envelope);
+    }
 };
 
 pub fn DmaSound(comptime kind: DmaSoundKind) type {
@@ -285,3 +615,141 @@ const DmaSoundKind = enum {
     A,
     B,
 };
+
+const FrameSequencer = struct {
+    const Self = @This();
+
+    step: u3,
+
+    pub fn init() Self {
+        return .{ .step = 0 };
+    }
+
+    pub fn tick(self: *Self) void {
+        self.step +%= 1;
+    }
+
+    fn lengthIsNext(self: *const Self) bool {
+        return (self.step +% 1) & 1 == 0; // Steps, 0, 2, 4, and 6 clock length
+    }
+};
+
+const Length = struct {
+    const Self = @This();
+
+    timer: u7,
+
+    pub fn init() Self {
+        return .{ .timer = 0 };
+    }
+
+    fn tick(self: *Self, freq: io.Frequency, ch_enabled: *bool) void {
+        const len_enable = freq.length_enable.read();
+
+        if (len_enable and self.timer > 0) {
+            self.timer -= 1;
+
+            // if length timer is now 0
+            if (self.timer == 0) ch_enabled.* = false;
+        }
+    }
+
+    fn ch4Tick(self: *Self, cnt: io.NoiseControl, ch_enabled: *bool) void {
+        const len_enable = cnt.length_enable.read();
+
+        if (len_enable and self.timer > 0) {
+            self.timer -= 1;
+
+            // if length timer is now 0
+            if (self.timer == 0) ch_enabled.* = false;
+        }
+    }
+};
+
+const Envelope = struct {
+    const Self = @This();
+
+    /// Period Timer
+    timer: u3,
+    /// Current Volume
+    vol: u4,
+
+    pub fn init() Self {
+        return .{ .timer = 0, .vol = 0 };
+    }
+
+    pub fn tick(self: *Self, cnt: io.Envelope) void {
+        if (cnt.period.read() != 0) {
+            if (self.timer != 0) self.timer -= 1;
+
+            if (self.timer == 0) {
+                self.timer = cnt.period.read();
+
+                if (cnt.direction.read()) {
+                    if (self.vol < 0xF) self.vol += 1;
+                } else {
+                    if (self.vol > 0x0) self.vol -= 1;
+                }
+            }
+        }
+    }
+};
+
+const SquareWave = struct {
+    const Self = @This();
+    const ticks: u64 = (1 << 24) / (1 << 22);
+
+    pos: u3,
+    sched: *Scheduler,
+    timer: u12,
+
+    pub fn init(sched: *Scheduler) Self {
+        return .{
+            .timer = 0,
+            .pos = 0,
+            .sched = sched,
+        };
+    }
+
+    /// Obscure NRx4 Behaviour
+    fn updateLength(_: *Self, fs: *const FrameSequencer, ch1: *ToneSweep, new_cnt: io.Frequency) void {
+        if (!fs.lengthIsNext() and !ch1.freq.length_enable.read() and new_cnt.length_enable.read() and ch1.len_dev.timer != 0) {
+            ch1.len_dev.timer -= 1;
+
+            if (ch1.len_dev.timer == 0 and !new_cnt.trigger.read()) ch1.enabled = false;
+        }
+    }
+
+    fn handleTimerOverflow(self: *Self, cnt: io.Frequency, late: u64) void {
+        const timer = (2048 - @as(u64, cnt.frequency.read())) * 4;
+
+        self.timer = @truncate(u12, timer);
+        self.pos = (self.pos +% 1) & 7;
+
+        self.sched.push(.{ .ApuChannel = 0 }, self.sched.now() + timer * ticks - late);
+    }
+
+    fn reloadTimer(self: *Self, value: u11) void {
+        self.sched.removeScheduledEvent(.{ .ApuChannel = 0 });
+
+        const tmp: u64 = (2048 - @as(u64, value)) * 4; // What Freq Timer should be assuming no weird behaviour
+        const timer = (tmp & ~@as(u64, 0x3)) | self.timer & 0x3; // Keep the last two bits from the old timer
+        self.timer = @truncate(u12, timer);
+
+        self.sched.push(.{ .ApuChannel = 0 }, self.sched.now() + timer * ticks);
+    }
+
+    fn sample(self: *const Self, cnt: io.Duty) u1 {
+        const pattern = cnt.pattern.read();
+
+        const i = self.pos ^ 7; // index of 0 should get highest bit
+        const result = switch (pattern) {
+            0b00 => @as(u8, 0b00000001) >> i, // 12.5%
+            0b01 => @as(u8, 0b00000011) >> i, // 25%
+            0b10 => @as(u8, 0b00001111) >> i, // 50%
+            0b11 => @as(u8, 0b11111100) >> i, // 75%
+        };
+
+        return @truncate(u1, result);
+    }
+};

src/bus/io.zig

@@ -118,7 +118,7 @@ pub fn read(bus: *const Bus, comptime T: type, address: u32) T {
             0x0400_0073 => bus.apu.ch3.vol.raw,
             0x0400_0079 => bus.apu.ch4.envelope.raw,
             0x0400_007C => bus.apu.ch4.poly.raw,
-            0x0400_0081 => @truncate(T, bus.apu.ch_vol_cnt.raw >> 8),
+            0x0400_0081 => @truncate(T, bus.apu.psg_cnt.raw >> 8),
             0x0400_0089 => @truncate(T, bus.apu.bias.raw >> 8),
 
             // Serial Communication 1
@@ -151,7 +151,7 @@ pub fn write(bus: *Bus, comptime T: type, address: u32, value: T) void {
 
             // Sound
             0x0400_0080 => {
-                bus.apu.ch_vol_cnt.raw = @truncate(u16, value);
+                bus.apu.psg_cnt.raw = @truncate(u16, value);
                 bus.apu.dma_cnt.raw = @truncate(u16, value >> 16);
             },
             0x0400_00A0 => bus.apu.chA.push(value),
@@ -232,7 +232,10 @@ pub fn write(bus: *Bus, comptime T: type, address: u32, value: T) void {
             0x0400_004E, 0x0400_0056 => {}, // Not used
 
             // Sound
-            0x0400_0080 => bus.apu.ch_vol_cnt.raw = value,
+            0x0400_0060 => bus.apu.ch1.sweep.raw = @truncate(u8, value),
+            0x0400_0062 => bus.apu.ch1.setSoundCntH(value),
+            0x0400_0064 => bus.apu.ch1.setFreq(&bus.apu.fs, value),
+            0x0400_0080 => bus.apu.psg_cnt.raw = value,
             0x0400_0082 => bus.apu.setDmaCnt(value),
             0x0400_0084 => bus.apu.setSoundCntX(value >> 7 & 1 == 1),
             0x0400_0088 => bus.apu.bias.raw = value,
@@ -314,7 +317,7 @@ pub fn write(bus: *Bus, comptime T: type, address: u32, value: T) void {
             0x0400_0062 => bus.apu.ch1.duty.raw = value,
             0x0400_0063 => bus.apu.ch1.envelope.raw = value,
             0x0400_0064 => bus.apu.ch1.setFreqLow(value),
-            0x0400_0065 => bus.apu.ch1.setFreqHigh(value),
+            0x0400_0065 => bus.apu.ch1.setFreqHigh(&bus.apu.fs, value),
             0x0400_0068 => bus.apu.ch2.duty.raw = value,
             0x0400_0069 => bus.apu.ch2.envelope.raw = value,
             0x0400_006C => bus.apu.ch2.setFreqLow(value),
@@ -578,8 +581,8 @@ pub const NoiseControl = extern union {
 
 /// Read / Write
 pub const ChannelVolumeControl = extern union {
-    left_vol: Bitfield(u16, 0, 3),
-    right_vol: Bitfield(u16, 4, 3),
+    right_vol: Bitfield(u16, 0, 3),
+    left_vol: Bitfield(u16, 4, 3),
 
     ch1_right: Bit(u16, 8),
     ch2_right: Bit(u16, 9),

src/scheduler.zig

@@ -51,6 +51,13 @@ pub const Scheduler = struct {
                         3 => cpu.bus.tim._3.handleOverflow(cpu, late),
                     }
                 },
+                .ApuChannel => |id| {
+                    switch (id) {
+                        0 => cpu.bus.apu.ch1.channelTimerOverflow(late),
+                        else => {},
+                    }
+                },
+                .FrameSequencer => cpu.bus.apu.tickFrameSequencer(late),
                 .SampleAudio => cpu.bus.apu.sampleAudio(late),
                 .HBlank => cpu.bus.ppu.handleHBlankEnd(cpu, late), // The end of a HBlank
                 .VBlank => cpu.bus.ppu.handleHDrawEnd(cpu, late), // The end of a VBlank
@@ -104,4 +111,6 @@ pub const EventKind = union(enum) {
     Draw,
     TimerOverflow: u2,
     SampleAudio,
+    FrameSequencer,
+    ApuChannel: u2,
 };