in progress refactor

Needs profiling

.vscode/extensions.json

@@ -0,0 +1,8 @@
+{
+    "recommendations": [
+        "matklad.rust-analyzer",
+        "tamasfe.even-better-toml",
+        "serayuzgur.crates",
+        "vadimcn.vscode-lldb",
+    ]
+}

Cargo.toml

@@ -3,6 +3,7 @@ name = "gb"
 version = "0.1.0"
 authors = ["Rekai Musuka <rekai@musuka.dev>"]
 edition = "2018"
+resolver = "2"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
@@ -11,7 +12,7 @@ anyhow = "^1.0"
 bitfield = "^0.13"
 clap = "^2.33"
 gilrs = "^0.8"
-pixels = "^0.5"
+pixels = "^0.6"
 winit = "^0.25"
 winit_input_helper = "^0.10"
 rodio = "^0.14"

src/apu.rs

@@ -5,7 +5,8 @@ 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::{ChannelControl, FrameSequencerState, SoundOutput};
+use types::fs::{FrameSequencer, State as FrameSequencerState};
+use types::{ChannelControl, SoundOutput};
 
 pub mod gen;
 mod types;
@@ -25,9 +26,8 @@ pub struct Apu {
     /// Noise
     ch4: Channel4,
 
-    // Frame Sequencer
-    frame_seq_state: FrameSequencerState,
-    div_prev: Option<u8>,
+    sequencer: FrameSequencer,
+    div_prev: Option<u16>,
 
     prod: Option<SampleProducer<f32>>,
     sample_counter: u64,
@@ -43,11 +43,9 @@ impl BusIo for Apu {
             0x16 => self.ch2.duty(),
             0x17 => self.ch2.envelope(),
             0x19 => self.ch2.freq_hi(),
-            0x1A => self.ch3.enabled(),
-            0x1B => self.ch3.len(),
+            0x1A => self.ch3.dac_enabled(),
             0x1C => self.ch3.volume(),
             0x1E => self.ch3.freq_hi(),
-            0x20 => self.ch4.len(),
             0x21 => self.ch4.envelope(),
             0x22 => self.ch4.poly(),
             0x23 => self.ch4.frequency(),
@@ -73,7 +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),
@@ -96,92 +94,84 @@ impl BusIo for Apu {
 }
 
 impl Apu {
-    pub(crate) fn clock(&mut self, div: u16) {
-        use FrameSequencerState::*;
+    pub(crate) fn tick(&mut self, div: u16) {
         self.sample_counter += SAMPLE_INCREMENT;
 
-        // the 5th bit of the high byte
-        let bit_5 = (div >> 13 & 0x01) as u8;
+        // Frame Sequencer (512Hz)
+        if self.is_falling_edge(12, div) {
+            use FrameSequencerState::*;
 
-        if let Some(0x01) = self.div_prev {
-            if bit_5 == 0x00 {
-                // Falling Edge, step the Frame Sequencer
-                self.frame_seq_state.step();
-
-                match self.frame_seq_state {
-                    Step0Length => self.handle_length(),
-                    Step2LengthAndSweep => {
-                        self.handle_length();
-                        self.handle_sweep();
-                    }
-                    Step4Length => self.handle_length(),
-                    Step6LengthAndSweep => {
-                        self.handle_length();
-                        self.handle_sweep();
-                    }
-                    Step7VolumeEnvelope => self.handle_volume(),
-                    Step1Nothing | Step3Nothing | Step5Nothing => {}
-                };
+            match self.sequencer.state() {
+                Length => self.clock_length(),
+                LengthAndSweep => {
+                    self.clock_length();
+                    self.clock_sweep();
                 }
+                Envelope => self.clock_envelope(),
+                Nothing => {}
             }
 
-        self.ch1.clock();
-        self.ch2.clock();
-        self.ch3.clock();
-        self.ch4.clock();
+            self.sequencer.next();
+        }
 
-        self.div_prev = Some(bit_5);
+        self.div_prev = Some(div);
+
+        self.ch1.tick();
+        self.ch2.tick();
+        self.ch3.tick();
+        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;
-                    let ch1_right = self.ctrl.output.ch1_right() as u8 as f32 * ch1_amplitude;
 
-                    let ch2_amplitude = self.ch2.amplitude();
-                    let ch2_left = self.ctrl.output.ch2_left() as u8 as f32 * ch2_amplitude;
-                    let ch2_right = self.ctrl.output.ch2_right() as u8 as f32 * ch2_amplitude;
+                    let (left, right) = self.ctrl.out.ch1();
+                    let ch1_left = if left { self.ch1.amplitude() } else { 0.0 };
+                    let ch1_right = if right { self.ch1.amplitude() } else { 0.0 };
 
-                    let ch3_amplitude = self.ch3.amplitude();
-                    let ch3_left = self.ctrl.output.ch3_left() as u8 as f32 * ch3_amplitude;
-                    let ch3_right = self.ctrl.output.ch3_right() as u8 as f32 * ch3_amplitude;
+                    let (left, right) = self.ctrl.out.ch2();
+                    let ch2_left = if left { self.ch2.amplitude() } else { 0.0 };
+                    let ch2_right = if right { self.ch2.amplitude() } else { 0.0 };
 
-                    let ch4_amplitude = self.ch4.amplitude();
-                    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, right) = self.ctrl.out.ch3();
+                    let ch3_left = if left { self.ch3.amplitude() } else { 0.0 };
+                    let ch3_right = if right { self.ch3.amplitude() } else { 0.0 };
 
-                    let left = (ch1_left + ch2_left + ch3_left + ch4_left) / 4.0;
-                    let right = (ch1_right + ch2_right + ch3_right + ch4_right) / 4.0;
+                    let (left, right) = self.ctrl.out.ch4();
+                    let ch4_left = if left { self.ch4.amplitude() } else { 0.0 };
+                    let ch4_right = if right { self.ch4.amplitude() } else { 0.0 };
 
-                    prod.push(left)
-                        .and(prod.push(right))
+                    let left_mixed = (ch1_left + ch2_left + ch3_left + ch4_left) / 4.0;
+                    let right_mixed = (ch1_right + ch2_right + ch3_right + ch4_right) / 4.0;
+
+                    let left_sample = (self.ctrl.channel.left_volume() + 1.0) * left_mixed;
+                    let right_sample = (self.ctrl.channel.right_volume() + 1.0) * right_mixed;
+
+                    prod.push(left_sample)
+                        .and(prod.push(right_sample))
                         .expect("Add samples to ring buffer");
                 }
             }
         }
     }
 
-    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
-            self.frame_seq_state = Default::default();
+            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 {
@@ -190,9 +180,11 @@ impl Apu {
         }
     }
 
-    fn reset(&mut self) {
-        // TODO: Clear readable sound registers
+    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();
         self.ch1.envelope = Default::default();
@@ -204,7 +196,7 @@ 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();
@@ -216,15 +208,16 @@ impl Apu {
         self.ch4.freq = Default::default();
 
         self.ctrl.channel = Default::default();
-        self.ctrl.output = Default::default();
+        self.ctrl.out = 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;
 
@@ -236,7 +229,7 @@ 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;
 
@@ -248,33 +241,33 @@ impl Apu {
         }
     }
 
-    fn handle_length(&mut self) {
-        Self::clock_length(
+    fn clock_length(&mut self) {
+        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;
         }
@@ -296,7 +289,7 @@ 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 {
@@ -316,27 +309,34 @@ 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 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,
+        }
+    }
 }
 
 #[derive(Debug, Default)]
@@ -344,7 +344,7 @@ pub(crate) struct SoundControl {
     /// 0xFF24 | NR50 - Channel Control
     channel: ChannelControl,
     /// 0xFF25 | NR51 - Selection of Sound output terminal
-    output: SoundOutput,
+    out: SoundOutput,
 
     enabled: bool,
 }
@@ -364,13 +364,13 @@ impl SoundControl {
 
     /// 0xFF25 | NR51 - Selection of Sound output terminal
     pub(crate) fn output(&self) -> u8 {
-        u8::from(self.output)
+        u8::from(self.out)
     }
 
     /// 0xFF25 | NR51 - Selection of Sound output terminal
     pub(crate) fn set_output(&mut self, byte: u8) {
         if self.enabled {
-            self.output = byte.into();
+            self.out = byte.into();
         }
     }
 
@@ -417,24 +417,6 @@ 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 {
-            // TODO: Why is this 2048?
-            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
@@ -463,7 +445,11 @@ 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)
@@ -482,22 +468,8 @@ impl Channel1 {
 
         // If this bit is set, a trigger event occurs
         if self.freq_hi.initial() {
-            // Envelope Behaviour during trigger event
-            self.period_timer = self.envelope.period();
-            self.current_volume = self.envelope.init_vol();
-
-            // Sweep behaviour during trigger event
-            let sweep_period = self.sweep.period();
-            let sweep_shift = self.sweep.shift_count();
-            self.shadow_freq = self.frequency();
-            self.sweep_timer = if sweep_period == 0 { 8 } else { sweep_period };
-
-            if sweep_period != 0 || sweep_shift != 0 {
-                self.sweep_enabled = true;
-            }
-
-            if sweep_shift != 0 {
-                let _ = self.calc_sweep_freq();
+            if self.is_dac_enabled() {
+                self.enabled = true;
             }
 
             // Length behaviour during trigger event
@@ -505,7 +477,44 @@ impl Channel1 {
                 self.length_timer = 64;
             }
 
-            self.enabled = true;
+            // Envelope Behaviour during trigger event
+            self.period_timer = self.envelope.period();
+            self.current_volume = self.envelope.init_vol();
+
+            // Sweep behaviour during trigger event
+            let sweep_period = self.sweep.period();
+            let sweep_shift = self.sweep.shift_count();
+
+            self.shadow_freq = self.frequency();
+            self.sweep_timer = if sweep_period == 0 { 8 } else { sweep_period };
+
+            self.sweep_enabled = sweep_period != 0 || sweep_shift != 0;
+
+            if sweep_shift != 0 {
+                let _ = self.calc_sweep_freq();
+            }
+        }
+    }
+
+    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() {
+            let sample = self.duty.wave_pattern().amplitude(self.duty_pos) * self.current_volume;
+            let input = if self.enabled { sample } else { 0 };
+
+            (input as f32 / 7.5) - 1.0
+        } else {
+            0.0
         }
     }
 
@@ -536,6 +545,10 @@ 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)]
@@ -563,24 +576,6 @@ 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 {
-            // TODO: Why is this 2048?
-            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
@@ -599,7 +594,11 @@ 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)
@@ -626,19 +625,47 @@ impl Channel2 {
                 self.length_timer = 64;
             }
 
+            if self.is_dac_enabled() {
                 self.enabled = true;
             }
         }
+    }
+
+    fn amplitude(&self) -> f32 {
+        if self.is_dac_enabled() {
+            let sample = self.duty.wave_pattern().amplitude(self.duty_pos) * self.current_volume;
+            let input = if self.enabled { sample } else { 0 };
+
+            (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
@@ -655,12 +682,14 @@ pub(crate) struct Channel3 {
 
     freq_timer: u16,
     offset: u8,
+
+    enabled: bool,
 }
 
 impl BusIo for Channel3 {
     fn read_byte(&self, addr: u16) -> u8 {
         if self.enabled {
-            self.wave_ram[self.offset as usize]
+            self.wave_ram[self.offset as usize / 2]
         } else {
             self.wave_ram[(addr - Self::WAVE_RAM_START_ADDR) as usize]
         }
@@ -668,7 +697,7 @@ impl BusIo for Channel3 {
 
     fn write_byte(&mut self, addr: u16, byte: u8) {
         if self.enabled {
-            self.wave_ram[self.offset as usize] = byte;
+            self.wave_ram[self.offset as usize / 2] = byte;
         } else {
             self.wave_ram[(addr - Self::WAVE_RAM_START_ADDR) as usize] = byte;
         }
@@ -679,18 +708,17 @@ impl Channel3 {
     const WAVE_RAM_START_ADDR: u16 = 0xFF30;
 
     /// 0xFF1A | NR30 - Channel 3 Sound on/off
-    pub(crate) fn enabled(&self) -> u8 {
-        ((self.enabled as u8) << 7) | 0x7F
+    pub(crate) fn dac_enabled(&self) -> u8 {
+        ((self.dac_enabled as u8) << 7) | 0x7F
     }
 
     /// 0xFF1A | NR30 - Channel 3 Sound on/off
-    pub(crate) fn set_enabled(&mut self, byte: u8) {
-        self.enabled = (byte >> 7) & 0x01 == 0x01;
-    }
+    pub(crate) fn set_dac_enabled(&mut self, byte: u8) {
+        self.dac_enabled = (byte >> 7) & 0x01 == 0x01;
 
-    /// 0xFF1B | NR31 - Sound Length
-    pub(crate) fn len(&self) -> u8 {
-        self.len | 0xFF
+        if !self.dac_enabled {
+            self.enabled = false;
+        }
     }
 
     /// 0xFF1B | NR31 - Sound Length
@@ -737,17 +765,13 @@ 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();
-
-        (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;
         }
@@ -758,6 +782,17 @@ impl Channel3 {
         }
     }
 
+    fn amplitude(&self) -> f32 {
+        if self.dac_enabled {
+            let sample = self.read_sample(self.offset) >> self.volume.shift_count();
+            let input = if self.enabled { sample } else { 0 };
+
+            (input as f32 / 7.5) - 1.0
+        } else {
+            0.0
+        }
+    }
+
     fn read_sample(&self, index: u8) -> u8 {
         let i = (index / 2) as usize;
 
@@ -802,15 +837,10 @@ pub(crate) struct Channel4 {
 }
 
 impl Channel4 {
-    /// 0xFF20 | NR41 - Channel 4 Sound Length
-    pub(crate) fn len(&self) -> u8 {
-        self.len | 0xFF
-    }
-
     /// 0xFF20 | NR41 - Channel 4 Sound Length
     pub(crate) fn set_len(&mut self, byte: u8) {
         self.len = byte & 0x3F;
-        self.length_timer = 256 - self.len as u16;
+        self.length_timer = 64 - self.len as u16;
     }
 
     /// 0xFF21 | NR42 - Channel 4 Volume Envelope
@@ -820,7 +850,11 @@ 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
@@ -855,17 +889,13 @@ 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;
         }
@@ -883,6 +913,21 @@ impl Channel4 {
         }
     }
 
+    fn amplitude(&self) -> f32 {
+        if self.is_dac_enabled() {
+            let sample = (!self.lf_shift & 0x01) as u8 * self.current_volume;
+            let input = if self.enabled { sample } else { 0 };
+
+            (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

@@ -3,7 +3,7 @@ use rtrb::{Consumer, Producer, PushError, RingBuffer};
 
 pub(crate) const SAMPLE_RATE: u32 = 48000; // Hz
 const CHANNEL_COUNT: usize = 2;
-const BUFFER_CAPACITY: usize = 4096 * CHANNEL_COUNT; // # of samples * the # of channels
+const BUFFER_CAPACITY: usize = 2048 * CHANNEL_COUNT; // # of samples * the # of channels
 
 pub struct AudioSPSC<T> {
     inner: RingBuffer<T>,
@@ -43,11 +43,12 @@ impl<T> SampleProducer<T> {
         self.inner.push(value)
     }
 
+    #[allow(dead_code)]
     pub(crate) fn available(&self) -> bool {
         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! {
@@ -178,7 +178,7 @@ pub(crate) mod ch4 {
         pub struct Frequency(u8);
         impl Debug;
         _initial, _: 7;
-        _length_disable, _: 6; // TODO: same as FrequencyHigh, figure out what this is
+        _length_disable, _: 6;
     }
 
     impl Frequency {
@@ -217,14 +217,14 @@ pub(crate) mod ch4 {
     }
 }
 
-pub(crate) mod common {
+pub(super) mod common {
     use super::bitfield;
 
     bitfield! {
         pub struct FrequencyHigh(u8);
         impl Debug;
         _initial, _: 7;
-        _length_disable, _: 6; // TODO: Figure out what the hell this is
+        _length_disable, _: 6;
         pub freq_bits, set_freq_bits: 2, 0;
     }
 
@@ -342,7 +342,7 @@ pub(crate) mod common {
         pub struct SoundDuty(u8);
         impl Debug;
         from into WavePattern, _wave_pattern, _: 7, 6;
-        _sound_length, _: 5, 0; // TODO: Getter only used if bit 6 in NR14 is set
+        _sound_length, _: 5, 0;
     }
 
     impl SoundDuty {
@@ -427,41 +427,6 @@ pub(crate) mod common {
     }
 }
 
-#[derive(Debug, Clone, Copy)]
-pub(crate) enum FrameSequencerState {
-    Step0Length,
-    Step1Nothing,
-    Step2LengthAndSweep,
-    Step3Nothing,
-    Step4Length,
-    Step5Nothing,
-    Step6LengthAndSweep,
-    Step7VolumeEnvelope,
-}
-
-impl FrameSequencerState {
-    pub(crate) fn step(&mut self) {
-        use FrameSequencerState::*;
-
-        *self = match *self {
-            Step0Length => Step1Nothing,
-            Step1Nothing => Step2LengthAndSweep,
-            Step2LengthAndSweep => Step3Nothing,
-            Step3Nothing => Step4Length,
-            Step4Length => Step5Nothing,
-            Step5Nothing => Step6LengthAndSweep,
-            Step6LengthAndSweep => Step7VolumeEnvelope,
-            Step7VolumeEnvelope => Step0Length,
-        };
-    }
-}
-
-impl Default for FrameSequencerState {
-    fn default() -> Self {
-        Self::Step0Length
-    }
-}
-
 bitfield! {
     pub struct SoundOutput(u8);
     impl Debug;
@@ -475,6 +440,24 @@ bitfield! {
     pub ch1_right, _: 0;
 }
 
+impl SoundOutput {
+    pub(super) fn ch1(&self) -> (bool, bool) {
+        (self.ch1_left(), self.ch1_right())
+    }
+
+    pub(super) fn ch2(&self) -> (bool, bool) {
+        (self.ch2_left(), self.ch2_right())
+    }
+
+    pub(super) fn ch3(&self) -> (bool, bool) {
+        (self.ch3_left(), self.ch3_right())
+    }
+
+    pub(super) fn ch4(&self) -> (bool, bool) {
+        (self.ch4_left(), self.ch4_right())
+    }
+}
+
 impl Copy for SoundOutput {}
 impl Clone for SoundOutput {
     fn clone(&self) -> Self {
@@ -503,10 +486,20 @@ impl From<SoundOutput> for u8 {
 bitfield! {
     pub struct ChannelControl(u8);
     impl Debug;
-    vin_so2, _: 7;
-    so2_level, _: 6, 4;
-    vin_so1, _: 3;
-    so1_level, _: 2, 0;
+    vin_left, _: 7;
+    _left_volume, _: 6, 4;
+    vin_right, _: 3;
+    _right_volume, _: 2, 0;
+}
+
+impl ChannelControl {
+    pub(crate) fn left_volume(&self) -> f32 {
+        self._left_volume() as f32
+    }
+
+    pub(crate) fn right_volume(&self) -> f32 {
+        self._right_volume() as f32
+    }
 }
 
 impl Copy for ChannelControl {}
@@ -533,3 +526,52 @@ 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/bus.rs

@@ -7,14 +7,13 @@ use crate::ppu::{Ppu, PpuMode};
 use crate::serial::Serial;
 use crate::timer::Timer;
 use crate::work_ram::{VariableWorkRam, WorkRam};
-use std::{fs::File, io::Read};
 
-const BOOT_ROM_SIZE: usize = 0x100;
+pub(crate) const BOOT_SIZE: usize = 0x100;
 
 #[derive(Debug)]
 pub struct Bus {
-    boot: Option<[u8; BOOT_ROM_SIZE]>, // Boot ROM is 256b long
-    cartridge: Option<Cartridge>,
+    boot: Option<[u8; BOOT_SIZE]>, // Boot ROM is 256b long
+    cart: Option<Cartridge>,
     pub(crate) ppu: Ppu,
     work_ram: WorkRam,
     var_ram: VariableWorkRam,
@@ -30,7 +29,7 @@ impl Default for Bus {
     fn default() -> Self {
         Self {
             boot: None,
-            cartridge: None,
+            cart: None,
             ppu: Default::default(),
             work_ram: Default::default(),
             var_ram: Default::default(),
@@ -45,25 +44,19 @@ impl Default for Bus {
 }
 
 impl Bus {
-    pub(crate) fn with_boot(path: &str) -> anyhow::Result<Self> {
-        let mut file = File::open(path)?;
-        let mut boot_rom = [0u8; 256];
-
-        file.read_exact(&mut boot_rom)?;
-
-        Ok(Self {
-            boot: Some(boot_rom),
+    pub(crate) fn with_boot(rom: [u8; 256]) -> Self {
+        Self {
+            boot: Some(rom),
             ..Default::default()
-        })
+        }
     }
 
-    pub(crate) fn load_cartridge(&mut self, path: &str) -> std::io::Result<()> {
-        self.cartridge = Some(Cartridge::new(path)?);
-        Ok(())
+    pub(crate) fn load_cart(&mut self, rom: Vec<u8>) {
+        self.cart = Some(Cartridge::new(rom));
     }
 
-    pub(crate) fn rom_title(&self) -> Option<&str> {
-        self.cartridge.as_ref()?.title()
+    pub(crate) fn cart_title(&self) -> Option<&str> {
+        self.cart.as_ref()?.title()
     }
 
     #[allow(dead_code)]
@@ -72,14 +65,20 @@ impl Bus {
     }
 
     pub(crate) fn clock(&mut self) {
-        self.ppu.clock();
-        self.timer.clock();
-        self.apu.clock(self.timer.divider);
-        self.clock_dma();
+        self.tick(4);
     }
 
-    fn clock_dma(&mut self) {
-        if let Some((src_addr, dest_addr)) = self.ppu.dma.clock() {
+    fn tick(&mut self, limit: u8) {
+        for _ in 0..limit {
+            self.timer.tick();
+            self.ppu.tick();
+            self.apu.tick(self.timer.divider);
+            self.dma_tick()
+        }
+    }
+
+    fn dma_tick(&mut self) {
+        if let Some((src_addr, dest_addr)) = self.ppu.dma.tick() {
             let byte = self.oam_read_byte(src_addr);
             self.oam_write_byte(dest_addr, byte);
         }
@@ -98,13 +97,13 @@ impl Bus {
                     }
                 }
 
-                match self.cartridge.as_ref() {
+                match self.cart.as_ref() {
                     Some(cart) => cart.read_byte(addr),
                     None => panic!("Tried to read from a non-existent cartridge"),
                 }
             }
             0x8000..=0x9FFF => self.ppu.read_byte(addr), // 8KB Video RAM
-            0xA000..=0xBFFF => match self.cartridge.as_ref() {
+            0xA000..=0xBFFF => match self.cart.as_ref() {
                 // 8KB External RAM
                 Some(cart) => cart.read_byte(addr),
                 None => panic!("Tried to read from a non-existent cartridge"),
@@ -151,7 +150,7 @@ impl BusIo for Bus {
                     }
                 }
 
-                match self.cartridge.as_ref() {
+                match self.cart.as_ref() {
                     Some(cart) => cart.read_byte(addr),
                     None => panic!("Tried to read from a non-existent cartridge"),
                 }
@@ -163,7 +162,7 @@ impl BusIo for Bus {
                     _ => self.ppu.read_byte(addr),
                 }
             }
-            0xA000..=0xBFFF => match self.cartridge.as_ref() {
+            0xA000..=0xBFFF => match self.cart.as_ref() {
                 // 8KB External RAM
                 Some(cart) => cart.read_byte(addr),
                 None => panic!("Tried to read from a non-existent cartridge"),
@@ -217,7 +216,7 @@ impl BusIo for Bus {
                     0x01 => self.serial.next,
                     0x02 => self.serial.ctrl.into(),
                     0x04 => (self.timer.divider >> 8) as u8,
-                    0x05 => self.timer.counter,
+                    0x05 => self.timer.tima(),
                     0x06 => self.timer.modulo,
                     0x07 => self.timer.ctrl.into(),
                     0x0F => self.interrupt_flag().into(),
@@ -234,7 +233,6 @@ impl BusIo for Bus {
                     0x49 => self.ppu.monochrome.obj_palette_1.into(),
                     0x4A => self.ppu.pos.window_y,
                     0x4B => self.ppu.pos.window_x,
-                    0x4D => 0xFF, // TODO: CGB Specific Register
                     _ => {
                         eprintln!("Read 0xFF from unused IO register {:#06X}.", addr);
                         0xFF
@@ -257,7 +255,7 @@ impl BusIo for Bus {
             0x0000..=0x7FFF => {
                 // 16KB ROM bank 00 (ends at 0x3FFF)
                 // and 16KB ROM Bank 01 -> NN (switchable via MB)
-                match self.cartridge.as_mut() {
+                match self.cart.as_mut() {
                     Some(cart) => cart.write_byte(addr, byte),
                     None => panic!("Tried to write into non-existent cartridge"),
                 }
@@ -271,7 +269,7 @@ impl BusIo for Bus {
             }
             0xA000..=0xBFFF => {
                 // 8KB External RAM
-                match self.cartridge.as_mut() {
+                match self.cart.as_mut() {
                     Some(cart) => cart.write_byte(addr, byte),
                     None => panic!("Tried to write into non-existent cartridge"),
                 }
@@ -306,7 +304,7 @@ impl BusIo for Bus {
                     _ => {}
                 }
             }
-            0xFEA0..=0xFEFF => {} // TODO: As far as I know, writes to here do nothing.
+            0xFEA0..=0xFEFF => {} // FIXME: As far as I know, writes to here do nothing.
             0xFF00..=0xFF7F => {
                 // IO Registers
 
@@ -317,7 +315,7 @@ impl BusIo for Bus {
                     0x01 => self.serial.next = byte,
                     0x02 => self.serial.ctrl = byte.into(),
                     0x04 => self.timer.divider = 0x0000,
-                    0x05 => self.timer.counter = byte,
+                    0x05 => self.timer.set_tima(byte),
                     0x06 => self.timer.modulo = byte,
                     0x07 => self.timer.ctrl = byte.into(),
                     0x0F => self.set_interrupt_flag(byte),
@@ -368,17 +366,6 @@ impl BusIo for Bus {
     }
 }
 
-impl Bus {
-    pub(crate) fn read_word(&self, addr: u16) -> u16 {
-        (self.read_byte(addr + 1) as u16) << 8 | self.read_byte(addr) as u16
-    }
-
-    pub(crate) fn write_word(&mut self, addr: u16, word: u16) {
-        self.write_byte(addr + 1, (word >> 8) as u8);
-        self.write_byte(addr, (word & 0x00FF) as u8);
-    }
-}
-
 impl Bus {
     fn interrupt_flag(&self) -> InterruptFlag {
         // Read the current interrupt information from the PPU

src/cartridge.rs

@@ -1,7 +1,3 @@
-use std::fs::File;
-use std::io::{self, Read};
-use std::path::Path;
-
 use crate::bus::BusIo;
 
 const RAM_SIZE_ADDRESS: usize = 0x0149;
@@ -17,81 +13,45 @@ pub(crate) struct Cartridge {
 }
 
 impl Cartridge {
-    pub(crate) fn new<P: AsRef<Path> + ?Sized>(path: &P) -> io::Result<Self> {
-        let mut memory = vec![];
-        let mut rom = File::open(path)?;
-        rom.read_to_end(&mut memory)?;
-
+    pub(crate) fn new(memory: Vec<u8>) -> Self {
         let title = Self::find_title(&memory);
         eprintln!("Cartridge Title: {:?}", title);
 
-        Ok(Self {
+        Self {
             mbc: Self::detect_mbc(&memory),
             title,
             memory,
-        })
+        }
     }
 
     fn detect_mbc(memory: &[u8]) -> Box<dyn MBCIo> {
-        let ram_size = Self::find_ram_size(memory);
-        let bank_count = Self::find_bank_count(memory);
+        let ram_size = Self::detect_ram_info(memory);
+        let rom_size = Self::detect_rom_info(memory);
         let mbc_kind = Self::find_mbc(memory);
-        let ram_byte_count = ram_size.len();
+        let ram_cap = ram_size.capacity();
+        let rom_cap = rom_size.capacity();
 
-        eprintln!("Cartridge Ram Size: {} bytes", ram_size.len());
-        eprintln!("Cartridge ROM Size: {} bytes", bank_count.size());
+        eprintln!("Cartridge Ram Size: {} bytes", ram_cap);
+        eprintln!("Cartridge ROM Size: {} bytes", rom_size.capacity());
         eprintln!("MBC Type: {:?}", mbc_kind);
 
         match mbc_kind {
-            MBCKind::None => Box::new(NoMBC {}),
-            MBCKind::MBC1 => {
-                let mbc = MBC1 {
-                    ram_size,
-                    ram: vec![0; ram_byte_count as usize],
-                    bank_count,
-                    ..Default::default()
-                };
-
-                Box::new(mbc)
-            }
-            MBCKind::MBC1WithBattery => {
-                // TODO: Implement Saving
-                let mbc = MBC1 {
-                    ram_size,
-                    ram: vec![0; ram_byte_count as usize],
-                    bank_count,
-                    ..Default::default()
-                };
-
-                Box::new(mbc)
-            }
-            MBCKind::MBC3WithBattery => {
-                // TODO: Implement Saving
-                let mbc = MBC3 {
-                    ram_size,
-                    ram: vec![0; ram_byte_count as usize],
-                    ..Default::default()
-                };
-
-                Box::new(mbc)
-            }
-            MBCKind::MBC3 => {
-                let mbc = MBC3 {
-                    ram_size,
-                    ram: vec![0; ram_byte_count as usize],
-                    ..Default::default()
-                };
-
-                Box::new(mbc)
-            }
-            MBCKind::MBC5 => todo!("Implement MBC5"),
+            MBCKind::None => Box::new(NoMBC),
+            MBCKind::MBC1 => Box::new(MBC1::new(ram_size, rom_size)),
+            MBCKind::MBC1WithBattery => Box::new(MBC1::new(ram_size, rom_size)), // TODO: Implement Saving
+            MBCKind::MBC2 => Box::new(MBC2::new(rom_cap)),
+            MBCKind::MBC2WithBattery => Box::new(MBC2::new(rom_cap)), // TODO: Implement Saving
+            MBCKind::MBC3 => Box::new(MBC3::new(ram_cap)),
+            MBCKind::MBC3WithBattery => Box::new(MBC3::new(ram_cap)), // TODO: Implement Saving
+            MBCKind::MBC5 => Box::new(MBC5::new(ram_cap, rom_cap)),
+            MBCKind::MBC5WithBattery => Box::new(MBC5::new(ram_cap, rom_cap)), // TDO: Implement Saving
         }
     }
 
     fn find_title(memory: &[u8]) -> Option<String> {
         let slice = &memory[ROM_TITLE_RANGE];
         let with_nulls = std::str::from_utf8(slice).ok();
-        let trimmed = with_nulls.map(|s| s.trim_matches('\0'));
+        let trimmed = with_nulls.map(|s| s.trim_matches('\0').trim());
 
         match trimmed {
             Some("") | None => None,
@@ -103,29 +63,30 @@ impl Cartridge {
         self.title.as_deref()
     }
 
-    fn find_ram_size(memory: &[u8]) -> RamSize {
+    fn detect_ram_info(memory: &[u8]) -> RamSize {
         let id = memory[RAM_SIZE_ADDRESS];
         id.into()
     }
 
-    fn find_bank_count(memory: &[u8]) -> BankCount {
+    fn detect_rom_info(memory: &[u8]) -> RomSize {
         let id = memory[ROM_SIZE_ADDRESS];
         id.into()
     }
 
     fn find_mbc(memory: &[u8]) -> MBCKind {
-        let id = memory[MBC_TYPE_ADDRESS];
+        use MBCKind::*;
 
-        // TODO: Refactor this to match the other enums in this module
-        match id {
-            0x00 => MBCKind::None,
-            0x01 => MBCKind::MBC1,
-            0x02 => MBCKind::MBC1,
-            0x03 => MBCKind::MBC1WithBattery,
-            0x19 => MBCKind::MBC5,
-            0x13 => MBCKind::MBC3WithBattery,
-            0x11 => MBCKind::MBC3,
-            _ => unimplemented!("id {:#04X} is an unsupported MBC", id),
+        match memory[MBC_TYPE_ADDRESS] {
+            0x00 => None,
+            0x01 | 0x02 => MBC1,
+            0x03 => MBC1WithBattery,
+            0x05 => MBC2,
+            0x06 => MBC2WithBattery,
+            0x19 | 0x1A => MBC5,
+            0x1B => MBC5WithBattery,
+            0x13 => MBC3WithBattery,
+            0x11 | 0x12 => MBC3,
+            id => unimplemented!("id {:#04X} is an unsupported MBC", id),
         }
     }
 }
@@ -153,84 +114,82 @@ struct MBC1 {
     ram_bank: u8,
     mode: bool,
     ram_size: RamSize,
-    ram: Vec<u8>,
-    bank_count: BankCount,
-    ram_enabled: bool,
-}
-
-impl Default for MBC1 {
-    fn default() -> Self {
-        Self {
-            rom_bank: 0x01,
-            ram_bank: Default::default(),
-            mode: Default::default(),
-            ram_size: Default::default(),
-            ram: Default::default(),
-            bank_count: Default::default(),
-            ram_enabled: Default::default(),
-        }
-    }
+    memory: Vec<u8>,
+    rom_size: RomSize,
+    mem_enabled: bool,
 }
 
 impl MBC1 {
-    fn zero_bank(&self) -> u8 {
-        use BankCount::*;
+    fn new(ram_size: RamSize, rom_size: RomSize) -> Self {
+        Self {
+            rom_bank: 0x01,
+            memory: vec![0; ram_size.capacity() as usize],
+            ram_size,
+            rom_size,
+            ram_bank: Default::default(),
+            mode: Default::default(),
+            mem_enabled: Default::default(),
+        }
+    }
 
-        match self.bank_count {
+    fn zero_bank(&self) -> u8 {
+        use RomSize::*;
+
+        match self.rom_size {
             None | Four | Eight | Sixteen | ThirtyTwo => 0x00,
             SixtyFour => (self.ram_bank & 0x01) << 5,
-            OneHundredTwentyEight => (self.ram_bank & 0x03) << 5,
-            _ => unreachable!("{:?} is not a valid MBC1 BankCount", self.bank_count),
+            OneTwentyEight => (self.ram_bank & 0x03) << 5,
+            _ => unreachable!("{:?} is not a valid MBC1 BankCount", self.rom_size),
         }
     }
 
     fn _mbcm_zero_bank(&self) -> u8 {
-        use BankCount::*;
+        use RomSize::*;
 
-        match self.bank_count {
+        match self.rom_size {
             None | Four | Eight | Sixteen | ThirtyTwo => 0x00,
             SixtyFour => (self.ram_bank & 0x03) << 4,
-            OneHundredTwentyEight => (self.ram_bank & 0x03) << 5,
-            _ => unreachable!("{:?} is not a valid MBC1 BankCount", self.bank_count),
+            OneTwentyEight => (self.ram_bank & 0x03) << 5,
+            _ => unreachable!("{:?} is not a valid MBC1 BankCount", self.rom_size),
         }
     }
 
     fn high_bank(&self) -> u8 {
-        use BankCount::*;
+        use RomSize::*;
 
         let base = self.rom_bank & self.rom_size_mask();
 
-        match self.bank_count {
+        match self.rom_size {
             None | Four | Eight | Sixteen | ThirtyTwo => base,
             SixtyFour => base & !(0x01 << 5) | ((self.ram_bank & 0x01) << 5),
-            OneHundredTwentyEight => base & !(0x03 << 5) | ((self.ram_bank & 0x03) << 5),
-            _ => unreachable!("{:?} is not a valid MBC1 BankCount", self.bank_count),
+            OneTwentyEight => base & !(0x03 << 5) | ((self.ram_bank & 0x03) << 5),
+            _ => unreachable!("{:?} is not a valid MBC1 BankCount", self.rom_size),
         }
     }
 
     fn rom_size_mask(&self) -> u8 {
-        use BankCount::*;
+        use RomSize::*;
 
-        match self.bank_count {
+        match self.rom_size {
             None => 0b00000001,
             Four => 0b00000011,
             Eight => 0b00000111,
             Sixteen => 0b00001111,
-            ThirtyTwo | SixtyFour | OneHundredTwentyEight => 0b00011111,
-            _ => unreachable!("{:?} is not a valid MBC1 BankCount", self.bank_count),
+            ThirtyTwo | SixtyFour | OneTwentyEight => 0b00011111,
+            _ => unreachable!("{:?} is not a valid MBC1 BankCount", self.rom_size),
         }
     }
 
-    fn ram_addr(&self, addr: u16) -> u16 {
+    fn ram_addr(&self, addr: u16) -> usize {
         use RamSize::*;
 
         match self.ram_size {
-            _2KB | _8KB => (addr - 0xA000) % self.ram_size.len() as u16,
-            _32KB => {
+            Unused | One => (addr as usize - 0xA000) % self.ram_size.capacity(),
+            Four => {
                 if self.mode {
-                    0x2000 * self.ram_bank as u16 + (addr - 0xA000)
+                    0x2000 * self.ram_bank as usize + (addr as usize - 0xA000)
                 } else {
-                    addr - 0xA000
+                    addr as usize - 0xA000
                 }
             }
             _ => unreachable!("RAM size can not be greater than 32KB on MBC1"),
@@ -243,44 +202,34 @@ impl MBCIo for MBC1 {
         use MBCResult::*;
 
         match addr {
-            0x0000..=0x3FFF => {
-                if self.mode {
+            0x0000..=0x3FFF if self.mode => {
                 Address(0x4000 * self.zero_bank() as usize + addr as usize)
-                } else {
-                    Address(addr as usize)
-                }
             }
+            0x0000..=0x3FFF => Address(addr as usize),
             0x4000..=0x7FFF => {
                 Address(0x4000 * self.high_bank() as usize + (addr as usize - 0x4000))
             }
-            0xA000..=0xBFFF => {
-                if self.ram_enabled {
-                    Value(self.ram[self.ram_addr(addr) as usize])
-                } else {
-                    Value(0xFF)
-                }
+            0xA000..=0xBFFF if self.mem_enabled && self.ram_size != RamSize::None => {
+                Value(self.memory[self.ram_addr(addr)])
             }
+            0xA000..=0xBFFF => Value(0xFF),
             _ => unreachable!("A read from {:#06X} should not be handled by MBC1", addr),
         }
     }
 
     fn handle_write(&mut self, addr: u16, byte: u8) {
         match addr {
-            0x0000..=0x1FFF => self.ram_enabled = (byte & 0x0F) == 0x0A,
+            0x0000..=0x1FFF => self.mem_enabled = (byte & 0x0F) == 0x0A,
             0x2000..=0x3FFF => {
-                self.rom_bank = if byte == 0x00 {
-                    0x01
-                } else {
-                    byte & self.rom_size_mask()
-                };
-
-                self.rom_bank &= 0x1F;
+                let value = byte & 0x1F;
+                let masked_value = byte & self.rom_size_mask();
+                self.rom_bank = if value == 0 { 0x01 } else { masked_value };
             }
             0x4000..=0x5FFF => self.ram_bank = byte & 0x03,
             0x6000..=0x7FFF => self.mode = (byte & 0x01) == 0x01,
-            0xA000..=0xBFFF if self.ram_enabled => {
-                let ram_addr = self.ram_addr(addr) as usize;
-                self.ram[ram_addr] = byte;
+            0xA000..=0xBFFF if self.mem_enabled && self.ram_size != RamSize::None => {
+                let ram_addr = self.ram_addr(addr);
+                self.memory[ram_addr] = byte;
             }
             0xA000..=0xBFFF => {} // Ram isn't enabled, ignored write
             _ => unreachable!("A write to {:#06X} should not be handled by MBC1", addr),
@@ -294,22 +243,34 @@ enum MBC3Device {
     RealTimeClock,
 }
 
-#[derive(Debug, Default)]
+#[derive(Debug)]
 struct MBC3 {
     /// 7-bit Number
     rom_bank: u8,
     /// 2-bit Number
     ram_bank: u8,
 
-    devices_enabled: bool,
-    currently_mapped: Option<MBC3Device>,
-    ram_size: RamSize,
-    ram: Vec<u8>,
+    devs_enabled: bool,
+    mapped: Option<MBC3Device>,
+    memory: Vec<u8>,
 
     // RTC Data Latch Previous Write
     prev_latch_write: Option<u8>,
 }
 
+impl MBC3 {
+    fn new(ram_cap: usize) -> Self {
+        Self {
+            memory: vec![0; ram_cap],
+            rom_bank: Default::default(),
+            ram_bank: Default::default(),
+            devs_enabled: Default::default(),
+            mapped: Default::default(),
+            prev_latch_write: Default::default(),
+        }
+    }
+}
+
 impl MBCIo for MBC3 {
     fn handle_read(&self, addr: u16) -> MBCResult {
         use MBCResult::*;
@@ -317,11 +278,11 @@ impl MBCIo for MBC3 {
         let res = match addr {
             0x0000..=0x3FFF => Address(addr as usize),
             0x4000..=0x7FFF => Address(0x4000 * self.rom_bank as usize + (addr as usize - 0x4000)),
-            0xA000..=0xBFFF => match self.currently_mapped {
-                Some(MBC3Device::ExternalRam) if self.devices_enabled => {
-                    Value(self.ram[0x2000 * self.ram_bank as usize + (addr as usize - 0xA000)])
+            0xA000..=0xBFFF => match self.mapped {
+                Some(MBC3Device::ExternalRam) if self.devs_enabled => {
+                    Value(self.memory[0x2000 * self.ram_bank as usize + (addr as usize - 0xA000)])
                 }
-                Some(MBC3Device::RealTimeClock) if self.devices_enabled => {
+                Some(MBC3Device::RealTimeClock) if self.devs_enabled => {
                     todo!("Return Latched value of register")
                 }
                 _ => Value(0xFF),
@@ -334,7 +295,7 @@ impl MBCIo for MBC3 {
 
     fn handle_write(&mut self, addr: u16, byte: u8) {
         match addr {
-            0x000..=0x1FFF => self.devices_enabled = (byte & 0x0F) == 0x0A, // Enable External RAM and Access to RTC if there is one
+            0x000..=0x1FFF => self.devs_enabled = (byte & 0x0F) == 0x0A, // Enable External RAM and Access to RTC if there is one
             0x2000..=0x3FFF => {
                 self.rom_bank = match byte {
                     0x00 => 0x01,
@@ -344,10 +305,10 @@ impl MBCIo for MBC3 {
             0x4000..=0x5FFF => match byte {
                 0x00 | 0x01 | 0x02 | 0x03 => {
                     self.ram_bank = byte & 0x03;
-                    self.currently_mapped = Some(MBC3Device::ExternalRam);
+                    self.mapped = Some(MBC3Device::ExternalRam);
                 }
                 0x08 | 0x09 | 0x0A | 0x0B | 0x0C => {
-                    self.currently_mapped = Some(MBC3Device::RealTimeClock);
+                    self.mapped = Some(MBC3Device::RealTimeClock);
                 }
                 _ => {}
             },
@@ -359,11 +320,11 @@ impl MBCIo for MBC3 {
                 }
                 self.prev_latch_write = Some(byte);
             }
-            0xA000..=0xBFFF => match self.currently_mapped {
-                Some(MBC3Device::ExternalRam) if self.devices_enabled => {
-                    self.ram[0x2000 * self.ram_bank as usize + (addr as usize - 0xA000)] = byte
+            0xA000..=0xBFFF => match self.mapped {
+                Some(MBC3Device::ExternalRam) if self.devs_enabled => {
+                    self.memory[0x2000 * self.ram_bank as usize + (addr as usize - 0xA000)] = byte
                 }
-                Some(MBC3Device::RealTimeClock) if self.devices_enabled => {
+                Some(MBC3Device::RealTimeClock) if self.devs_enabled => {
                     todo!("Write to RTC")
                 }
                 _ => {}
@@ -374,7 +335,127 @@ impl MBCIo for MBC3 {
 }
 
 #[derive(Debug)]
-struct NoMBC {}
+struct MBC5 {
+    /// 9-bit number
+    rom_bank: u16,
+    /// 4-bit number
+    ram_bank: u8,
+
+    rom_cap: usize,
+
+    memory: Vec<u8>,
+    mem_enabled: bool,
+}
+
+impl MBC5 {
+    fn new(ram_cap: usize, rom_cap: usize) -> Self {
+        Self {
+            rom_bank: 0x01,
+            memory: vec![0; ram_cap],
+            rom_cap,
+            ram_bank: Default::default(),
+            mem_enabled: Default::default(),
+        }
+    }
+
+    fn bank_addr(&self, addr: u16) -> usize {
+        (0x4000 * self.rom_bank as usize + (addr as usize - 0x4000)) % self.rom_cap
+    }
+}
+
+impl MBCIo for MBC5 {
+    fn handle_read(&self, addr: u16) -> MBCResult {
+        use MBCResult::*;
+
+        match addr {
+            0x0000..=0x3FFF => Address(addr as usize),
+            0x4000..=0x7FFF => Address(self.bank_addr(addr)),
+            0xA000..=0xBFFF if self.mem_enabled => {
+                Value(self.memory[0x2000 * self.ram_bank as usize + (addr as usize - 0xA000)])
+            }
+            0xA000..=0xBFFF => Value(0xFF),
+            _ => unreachable!("A read from {:#06X} should not be handled by MBC5", addr),
+        }
+    }
+
+    fn handle_write(&mut self, addr: u16, byte: u8) {
+        match addr {
+            0x0000..=0x1FFF => self.mem_enabled = (byte & 0x0F) == 0x0A,
+            0x2000..=0x2FFF => self.rom_bank = (self.rom_bank & 0x0100) | byte as u16,
+            0x3000..=0x3FFF => self.rom_bank = (self.rom_bank & 0x00FF) | (byte as u16 & 0x01) << 8,
+            0x4000..=0x5FFF => self.ram_bank = byte & 0x0F,
+            0xA000..=0xBFFF if self.mem_enabled => {
+                self.memory[0x2000 * self.ram_bank as usize + (addr as usize - 0xA000)] = byte;
+            }
+            0xA000..=0xBFFF => {}
+            _ => unreachable!("A write to {:#06X} should not be handled by MBC5", addr),
+        }
+    }
+}
+
+#[derive(Debug)]
+struct MBC2 {
+    /// 4-bit number
+    rom_bank: u8,
+    memory: Box<[u8; Self::RAM_SIZE]>,
+    mem_enabled: bool,
+
+    rom_cap: usize,
+}
+
+impl MBC2 {
+    const RAM_SIZE: usize = 0x0200;
+
+    fn new(rom_cap: usize) -> Self {
+        Self {
+            rom_bank: 0x01,
+            memory: Box::new([0; Self::RAM_SIZE]),
+            mem_enabled: Default::default(),
+            rom_cap,
+        }
+    }
+
+    fn rom_addr(&self, addr: u16) -> usize {
+        (0x4000 * self.rom_bank as usize + (addr as usize - 0x4000)) % self.rom_cap
+    }
+}
+
+impl MBCIo for MBC2 {
+    fn handle_read(&self, addr: u16) -> MBCResult {
+        use MBCResult::*;
+
+        match addr {
+            0x0000..=0x3FFF => Address(addr as usize),
+            0x4000..=0x7FFF => Address(self.rom_addr(addr)),
+            0xA000..=0xBFFF if self.mem_enabled => {
+                let mbc2_addr = addr as usize & (Self::RAM_SIZE - 1);
+                Value(self.memory[mbc2_addr] | 0xF0)
+            }
+            0xA000..=0xBFFF => Value(0xFF),
+            _ => unreachable!("A read from {:#06X} should not be handled by MBC2", addr),
+        }
+    }
+
+    fn handle_write(&mut self, addr: u16, byte: u8) {
+        let nybble = byte & 0x0F;
+
+        match addr {
+            0x0000..=0x3FFF if addr >> 8 & 0x01 == 0x01 => {
+                self.rom_bank = if nybble == 0x00 { 0x01 } else { nybble };
+            }
+            0x0000..=0x3FFF => self.mem_enabled = nybble == 0x0A,
+            0xA000..=0xBFFF if self.mem_enabled => {
+                let mbc2_addr = addr as usize & (Self::RAM_SIZE - 1);
+                self.memory[mbc2_addr] = nybble;
+            }
+            0x4000..=0x7FFF | 0xA000..=0xBFFF => {}
+            _ => unreachable!("A write to {:#06X} should not be handled by MBC2", addr),
+        }
+    }
+}
+
+#[derive(Debug)]
+struct NoMBC;
 
 impl MBCIo for NoMBC {
     fn handle_read(&self, addr: u16) -> MBCResult {
@@ -402,9 +483,12 @@ enum MBCKind {
     None,
     MBC1,
     MBC1WithBattery,
-    MBC5,
-    MBC3WithBattery,
+    MBC2,
+    MBC2WithBattery,
     MBC3,
+    MBC3WithBattery,
+    MBC5,
+    MBC5WithBattery,
 }
 
 impl Default for MBCKind {
@@ -413,27 +497,27 @@ impl Default for MBCKind {
     }
 }
 
-#[derive(Debug, Clone, Copy)]
+#[derive(Debug, Clone, Copy, PartialEq)]
 enum RamSize {
     None = 0x00,
-    _2KB = 0x01,
-    _8KB = 0x02,
-    _32KB = 0x03,  // Split into 4 RAM banks
-    _128KB = 0x04, // Split into 16 RAM banks
-    _64KB = 0x05,  // Split into 8 RAm Banks
+    Unused = 0x01,
+    One = 0x02,
+    Four = 0x03,
+    Sixteen = 0x04,
+    Eight = 0x05,
 }
 
 impl RamSize {
-    fn len(&self) -> u32 {
+    fn capacity(&self) -> usize {
         use RamSize::*;
 
         match *self {
             None => 0,
-            _2KB => 2_048,
-            _8KB => 8_192,
-            _32KB => 32_768,
-            _128KB => 131_072,
-            _64KB => 65_536,
+            Unused => 0x800,
+            One => 0x2000,
+            Four => 0x8000,
+            Sixteen => 0x20000,
+            Eight => 0x10000,
         }
     }
 }
@@ -450,63 +534,49 @@ impl From<u8> for RamSize {
 
         match byte {
             0x00 => None,
-            0x01 => _2KB,
-            0x02 => _8KB,
-            0x03 => _32KB,
-            0x04 => _128KB,
-            0x05 => _64KB,
+            0x01 => Unused,
+            0x02 => One,
+            0x03 => Four,
+            0x04 => Sixteen,
+            0x05 => Eight,
             _ => unreachable!("{:#04X} is not a valid value for RAMSize", byte),
         }
     }
 }
 
 #[derive(Debug, Clone, Copy)]
-enum BankCount {
+enum RomSize {
     None = 0x00,              // 32KB (also called Two)
     Four = 0x01,              // 64KB
     Eight = 0x02,             // 128KB
     Sixteen = 0x03,           // 256KB
     ThirtyTwo = 0x04,         // 512KB
     SixtyFour = 0x05,         // 1MB
-    OneHundredTwentyEight = 0x06, // 2MB
-    TwoHundredFiftySix = 0x07,    // 4MB
+    OneTwentyEight = 0x06,    // 2MB
+    TwoFiftySix = 0x07,       // 4MB
     FiveHundredTwelve = 0x08, // 8MB
     SeventyTwo = 0x52,        // 1.1MB
     Eighty = 0x53,            // 1.2MB
     NinetySix = 0x54,         // 1.5MB
 }
 
-impl Default for BankCount {
-    fn default() -> Self {
-        Self::None
-    }
-}
-
-impl BankCount {
+impl RomSize {
     // https://hacktix.github.io/GBEDG/mbcs/#rom-size
-    fn size(&self) -> u32 {
-        use BankCount::*;
+    fn capacity(&self) -> usize {
+        use RomSize::*;
 
         match self {
-            None => 32_768,
-            Four => 65_536,
-            Eight => 131_072,
-            Sixteen => 262_144,
-            ThirtyTwo => 524_288,
-            SixtyFour => 1_048_576,
-            OneHundredTwentyEight => 2_097_152,
-            TwoHundredFiftySix => 4_194_304,
-            FiveHundredTwelve => 8_388_608,
-            SeventyTwo => 1_179_648,
-            Eighty => 1_310_720,
-            NinetySix => 1_572_864,
+            SeventyTwo => 0x120000,
+            Eighty => 0x140000,
+            NinetySix => 0x180000,
+            _ => 0x8000 << *self as u8,
         }
     }
 }
 
-impl From<u8> for BankCount {
+impl From<u8> for RomSize {
     fn from(byte: u8) -> Self {
-        use BankCount::*;
+        use RomSize::*;
 
         match byte {
             0x00 => None,
@@ -515,8 +585,8 @@ impl From<u8> for BankCount {
             0x03 => Sixteen,
             0x04 => ThirtyTwo,
             0x05 => SixtyFour,
-            0x06 => OneHundredTwentyEight,
-            0x07 => TwoHundredFiftySix,
+            0x06 => OneTwentyEight,
+            0x07 => TwoFiftySix,
             0x08 => FiveHundredTwelve,
             0x52 => SeventyTwo,
             0x53 => Eighty,
@@ -534,6 +604,6 @@ impl std::fmt::Debug for Box<dyn MBCIo> {
 
 impl Default for Box<dyn MBCIo> {
     fn default() -> Self {
-        Box::new(MBC1::default())
+        Box::new(NoMBC)
     }
 }

src/cpu.rs

@@ -1,10 +1,7 @@
-use crate::apu::Apu;
-use crate::bus::{Bus, BusIo};
-use crate::instruction::cycle::Cycle;
+use crate::bus::{Bus, BusIo, BOOT_SIZE};
 use crate::instruction::Instruction;
 use crate::interrupt::{InterruptEnable, InterruptFlag};
-use crate::joypad::Joypad;
-use crate::ppu::Ppu;
+use crate::Cycle;
 use bitfield::bitfield;
 use std::fmt::{Display, Formatter, Result as FmtResult};
 
@@ -14,13 +11,11 @@ pub struct Cpu {
     reg: Registers,
     flags: Flags,
     ime: ImeState,
-    // TODO: Merge halted and state properties
-    halted: Option<HaltState>,
     state: State,
 }
 
 impl Cpu {
-    pub fn new() -> Self {
+    pub(crate) fn without_boot() -> Self {
         Self {
             reg: Registers {
                 a: 0x01,
@@ -38,114 +33,115 @@ impl Cpu {
         }
     }
 
-    pub fn boot_new(path: &str) -> anyhow::Result<Self> {
-        Ok(Self {
-            bus: Bus::with_boot(path)?,
+    pub(crate) fn with_boot(rom: [u8; BOOT_SIZE]) -> Self {
+        Self {
+            bus: Bus::with_boot(rom),
             ..Default::default()
-        })
+        }
     }
 
-    pub(crate) fn ime(&self) -> &ImeState {
-        &self.ime
+    pub(crate) fn ime(&self) -> ImeState {
+        self.ime
     }
 
     pub(crate) fn set_ime(&mut self, state: ImeState) {
         self.ime = state;
     }
 
-    pub(crate) fn halt(&mut self, state: HaltState) {
-        self.halted = Some(state);
+    pub(crate) fn halt_cpu(&mut self, kind: HaltKind) {
+        self.state = State::Halt(kind);
     }
 
-    fn resume(&mut self) {
-        self.halted = None;
+    fn resume_execution(&mut self) {
+        self.state = State::Execute;
     }
 
-    pub(crate) fn halted(&self) -> Option<&HaltState> {
-        self.halted.as_ref()
+    pub(crate) fn is_halted(&self) -> bool {
+        match self.state {
+            State::Halt(_) => true,
+            _ => false,
+        }
     }
 
-    fn inc_pc(&mut self) {
-        self.reg.pc += 1;
+    pub(crate) fn halt_kind(&self) -> Option<HaltKind> {
+        match self.state {
+            State::Halt(kind) => Some(kind),
+            _ => None,
         }
-
-    pub fn load_cartridge(&mut self, path: &str) -> std::io::Result<()> {
-        self.bus.load_cartridge(path)
-    }
-
-    pub fn rom_title(&self) -> Option<&str> {
-        self.bus.rom_title()
     }
 }
 
 impl Cpu {
-    fn fetch(&self) -> u8 {
-        self.bus.read_byte(self.reg.pc)
-    }
-
-    pub(crate) fn imm_byte(&mut self) -> u8 {
-        let byte = self.bus.read_byte(self.reg.pc);
+    /// Fetch an [Instruction] from the memory bus
+    /// (4 cycles)
+    fn fetch(&mut self) -> u8 {
+        let byte = self.read_byte(self.reg.pc);
+        self.bus.clock();
         self.reg.pc += 1;
         byte
     }
 
-    pub(crate) fn imm_word(&mut self) -> u16 {
-        let word = self.bus.read_word(self.reg.pc);
-        self.reg.pc += 2;
-        word
-    }
-
+    /// Decode a byte into an [SM83](Cpu) [Instruction]
+    ///
+    /// If opcode == 0xCB, then decoding costs 4 cycles.
+    /// Otherwise, decoding is free
     pub(crate) fn decode(&mut self, opcode: u8) -> Instruction {
         if opcode == 0xCB {
-            Instruction::decode(self.imm_byte(), true)
+            Instruction::decode(self.fetch(), true)
         } else {
             Instruction::decode(opcode, false)
         }
     }
 
+    /// Execute an [Instruction].
+    ///
+    /// The amount of cycles necessary to execute an instruction range from
+    /// 0 to 20 T-cycles
     fn execute(&mut self, instruction: Instruction) -> Cycle {
         Instruction::execute(self, instruction)
     }
 
+    /// Perform the [`Cpu::fetch()`] [`Cpu::decode()`] [`Cpu::execute()`]
+    /// routine.
+    ///
+    /// Handle HALT and interrupts.
     pub fn step(&mut self) -> Cycle {
         // Log instructions
-        // if !self.bus.boot_mapped() {
+        // if self.reg.pc > 0xFF {
         //     let out = std::io::stdout();
-        //     let _ = self._log_state(out.lock());
+        //     let _ = self._print_logs(out.lock());
         // }
 
-        // FIXME: The Halt instruction takes less cycles than it should in Blargg's 2nd cpu_instrs test
-        let cycles = match self.halted() {
-            Some(state) => {
-                use HaltState::*;
+        if let Some(elapsed) = self.handle_interrupt() {
+            return elapsed;
+        }
 
-                match state {
-                    ImeEnabled | NonePending => Cycle::new(4),
+        if let Some(kind) = self.halt_kind() {
+            use HaltKind::*;
+
+            self.bus.clock();
+
+            let elapsed = match kind {
+                ImeEnabled | NonePending => 4,
                 SomePending => todo!("Implement HALT bug"),
-                }
-            }
-            None => {
-                let opcode = self.fetch();
-                self.inc_pc();
-
-                let instr = self.decode(opcode);
-                let cycles = self.execute(instr);
-
-                self.check_ime();
-
-                cycles
-            }
             };
 
-        let pending: u32 = cycles.into();
-        for _ in 0..pending {
-            self.bus.clock();
+            return elapsed;
         }
 
-        // TODO: This is in the wrong place
-        self.handle_interrupts();
+        let opcode = self.fetch();
+        let instr = self.decode(opcode);
+        let elapsed = self.execute(instr);
+        self.handle_ei();
 
-        cycles
+        // For use in Blargg's Test ROMs
+        if self.read_byte(0xFF02) == 0x81 {
+            let c = self.read_byte(0xFF01) as char;
+            self.write_byte(0xFF02, 0x00);
+            eprint!("{}", c);
+        }
+
+        elapsed
     }
 }
 
@@ -160,87 +156,80 @@ impl BusIo for Cpu {
 }
 
 impl Cpu {
-    pub(crate) fn write_word(&mut self, addr: u16, word: u16) {
-        self.bus.write_word(addr, word)
-    }
-}
-
-impl Cpu {
-    pub fn ppu(&mut self) -> &Ppu {
-        &self.bus.ppu
+    pub(crate) fn bus(&self) -> &Bus {
+        &self.bus
     }
 
-    pub fn apu_mut(&mut self) -> &mut Apu {
-        &mut self.bus.apu
+    pub(crate) fn bus_mut(&mut self) -> &mut Bus {
+        &mut self.bus
     }
 
-    pub(crate) fn joypad_mut(&mut self) -> &mut Joypad {
-        &mut self.bus.joypad
-    }
-
-    fn check_ime(&mut self) {
+    fn handle_ei(&mut self) {
         match self.ime {
-            ImeState::Pending => {
-                // This is within the context of the EI instruction, we need to not update EI until the end of the
-                // next executed Instruction
-                self.ime = ImeState::PendingEnd;
-            }
-            ImeState::PendingEnd => {
-                // The Instruction after EI has now been executed, so we want to enable the IME flag here
-                self.ime = ImeState::Enabled;
-            }
-            ImeState::Disabled | ImeState::Enabled => {} // Do Nothing
+            ImeState::EiExecuted => self.ime = ImeState::Pending,
+            ImeState::Pending => self.ime = ImeState::Enabled,
+            ImeState::Disabled | ImeState::Enabled => {}
         }
     }
 
-    fn handle_interrupts(&mut self) {
-        let req = self.read_byte(0xFF0F);
-        let enabled = self.read_byte(0xFFFF);
+    pub(crate) fn int_request(&self) -> u8 {
+        self.read_byte(0xFF0F)
+    }
 
-        if self.halted.is_some() {
+    pub(crate) fn int_enable(&self) -> u8 {
+        self.read_byte(0xFFFF)
+    }
+
+    fn handle_interrupt(&mut self) -> Option<Cycle> {
+        let irq = self.int_request();
+        let enable = self.int_enable();
+
+        // TODO: Ensure that this behaviour is correct
+        if self.is_halted() {
             // When we're here either a HALT with IME set or
             // a HALT with IME not set and No pending Interrupts was called
 
-            if req & enabled != 0 {
+            if irq & enable != 0 {
                 // The if self.ime() below correctly follows the "resuming from HALT" behaviour so
                 // nothing actually needs to be added here. This is just documentation
                 // since it's a bit weird why nothing is being done
 
-                self.resume()
+                self.resume_execution();
             }
         }
 
-        if let ImeState::Enabled = self.ime() {
-            let mut req: InterruptFlag = req.into();
-            let enabled: InterruptEnable = enabled.into();
+        match self.ime() {
+            ImeState::Enabled => {
+                let mut irq: InterruptFlag = irq.into();
+                let enable: InterruptEnable = enable.into();
 
-            let vector = if req.vblank() && enabled.vblank() {
+                let rst_vector = if irq.vblank() && enable.vblank() {
                     // Handle VBlank Interrupt
-                req.set_vblank(false);
+                    irq.set_vblank(false);
 
                     // INT 40h
                     Some(0x40)
-            } else if req.lcd_stat() && enabled.lcd_stat() {
+                } else if irq.lcd_stat() && enable.lcd_stat() {
                     // Handle LCD STAT Interrupt
-                req.set_lcd_stat(false);
+                    irq.set_lcd_stat(false);
 
                     // INT 48h
                     Some(0x48)
-            } else if req.timer() && enabled.timer() {
+                } else if irq.timer() && enable.timer() {
                     // Handle Timer Interrupt
-                req.set_timer(false);
+                    irq.set_timer(false);
 
                     // INT 50h
                     Some(0x50)
-            } else if req.serial() && enabled.serial() {
+                } else if irq.serial() && enable.serial() {
                     // Handle Serial Interrupt
-                req.set_serial(false);
+                    irq.set_serial(false);
 
                     // INT 58h
                     Some(0x58)
-            } else if req.joypad() && enabled.joypad() {
+                } else if irq.joypad() && enable.joypad() {
                     // Handle Joypad Interrupt
-                req.set_joypad(false);
+                    irq.set_joypad(false);
 
                     // INT 60h
                     Some(0x60)
@@ -248,17 +237,19 @@ impl Cpu {
                     None
                 };
 
-            let _ = match vector {
-                Some(address) => {
+                match rst_vector {
+                    Some(vector) => {
                         //  Write the Changes to 0xFF0F and 0xFFFF registers
-                    self.write_byte(0xFF0F, req.into());
+                        self.write_byte(0xFF0F, irq.into());
 
                         // Disable all future interrupts
                         self.set_ime(ImeState::Disabled);
-                    Instruction::reset(self, address)
+                        Some(Instruction::reset(self, vector))
                     }
-                None => Cycle::new(0), // NO Interrupts were enabled and / or requested
-            };
+                    None => None,
+                }
+            }
+            _ => None,
         }
     }
 }
@@ -266,7 +257,7 @@ impl Cpu {
 #[derive(Debug, Clone, Copy)]
 enum State {
     Execute,
-    // Halt,
+    Halt(HaltKind),
     // Stop,
 }
 
@@ -363,10 +354,9 @@ impl Cpu {
 }
 
 impl Cpu {
-    fn _debug_log(&self, mut w: impl std::io::Write, instr: &Instruction) -> std::io::Result<()> {
-        let pc = self.reg.pc - 1;
+    fn _print_debug(&self, mut w: impl std::io::Write) -> std::io::Result<()> {
         write!(w, "A: {:02X} ", self.reg.a)?;
-        write!(w, "F: {:04b} ", u8::from(self.flags) >> 4)?;
+        write!(w, "F: {:02X} ", u8::from(self.flags))?;
         write!(w, "B: {:02X} ", self.reg.b)?;
         write!(w, "C: {:02X} ", self.reg.c)?;
         write!(w, "D: {:02X} ", self.reg.d)?;
@@ -374,31 +364,40 @@ impl Cpu {
         write!(w, "H: {:02X} ", self.reg.h)?;
         write!(w, "L: {:02X} ", self.reg.l)?;
         write!(w, "SP: {:04X} ", self.reg.sp)?;
-        write!(w, "PC: 00:{:04X} ", pc)?;
-        write!(w, "({:02X} ", self.read_byte(pc))?;
-        write!(w, "{:02X} ", self.read_byte(pc + 1))?;
-        write!(w, "{:02X} ", self.read_byte(pc + 2))?;
-        write!(w, "{:02X}) ", self.read_byte(pc + 3))?;
-        writeln!(w, "| {:?}", instr)?;
+        write!(w, "PC: 00:{:04X} ", self.reg.pc)?;
+        write!(w, "({:02X} ", self.read_byte(self.reg.pc))?;
+        write!(w, "{:02X} ", self.read_byte(self.reg.pc + 1))?;
+        write!(w, "{:02X} ", self.read_byte(self.reg.pc + 2))?;
+        write!(w, "{:02X})", self.read_byte(self.reg.pc + 3))?;
+        writeln!(w, "| {:?}", self._dbg_instr())?;
         w.flush()
     }
 
-    fn _log_state(&self, mut writer: impl std::io::Write) -> std::io::Result<()> {
-        write!(writer, "A: {:02X} ", self.reg.a)?;
-        write!(writer, "F: {:02X} ", u8::from(self.flags))?;
-        write!(writer, "B: {:02X} ", self.reg.b)?;
-        write!(writer, "C: {:02X} ", self.reg.c)?;
-        write!(writer, "D: {:02X} ", self.reg.d)?;
-        write!(writer, "E: {:02X} ", self.reg.e)?;
-        write!(writer, "H: {:02X} ", self.reg.h)?;
-        write!(writer, "L: {:02X} ", self.reg.l)?;
-        write!(writer, "SP: {:04X} ", self.reg.sp)?;
-        write!(writer, "PC: 00:{:04X} ", self.reg.pc)?;
-        write!(writer, "({:02X} ", self.read_byte(self.reg.pc))?;
-        write!(writer, "{:02X} ", self.read_byte(self.reg.pc + 1))?;
-        write!(writer, "{:02X} ", self.read_byte(self.reg.pc + 2))?;
-        writeln!(writer, "{:02X})", self.read_byte(self.reg.pc + 3))?;
-        writer.flush()
+    fn _print_logs(&self, mut w: impl std::io::Write) -> std::io::Result<()> {
+        write!(w, "A: {:02X} ", self.reg.a)?;
+        write!(w, "F: {:02X} ", u8::from(self.flags))?;
+        write!(w, "B: {:02X} ", self.reg.b)?;
+        write!(w, "C: {:02X} ", self.reg.c)?;
+        write!(w, "D: {:02X} ", self.reg.d)?;
+        write!(w, "E: {:02X} ", self.reg.e)?;
+        write!(w, "H: {:02X} ", self.reg.h)?;
+        write!(w, "L: {:02X} ", self.reg.l)?;
+        write!(w, "SP: {:04X} ", self.reg.sp)?;
+        write!(w, "PC: 00:{:04X} ", self.reg.pc)?;
+        write!(w, "({:02X} ", self.read_byte(self.reg.pc))?;
+        write!(w, "{:02X} ", self.read_byte(self.reg.pc + 1))?;
+        write!(w, "{:02X} ", self.read_byte(self.reg.pc + 2))?;
+        writeln!(w, "{:02X})", self.read_byte(self.reg.pc + 3))?;
+        w.flush()
+    }
+
+    fn _dbg_instr(&self) -> Instruction {
+        let byte = self.read_byte(self.reg.pc);
+        if byte == 0xCB {
+            Instruction::decode(self.read_byte(self.reg.pc + 1), true)
+        } else {
+            Instruction::decode(byte, false)
+        }
     }
 }
 
@@ -508,7 +507,7 @@ impl From<u8> for Flags {
 }
 
 #[derive(Debug, Clone, Copy)]
-pub(crate) enum HaltState {
+pub(crate) enum HaltKind {
     ImeEnabled,
     NonePending,
     SomePending,
@@ -517,8 +516,8 @@ pub(crate) enum HaltState {
 #[derive(Debug, Clone, Copy)]
 pub(crate) enum ImeState {
     Disabled,
+    EiExecuted,
     Pending,
-    PendingEnd,
     Enabled,
 }
 

src/emu.rs

@@ -1,73 +1,121 @@
-use crate::cpu::Cpu as SM83;
-use crate::instruction::cycle::Cycle;
-use crate::joypad;
-use crate::ppu::Ppu;
-use anyhow::Result;
+use crate::apu::gen::SampleProducer;
+use crate::cpu::Cpu;
+use crate::joypad::{self, Joypad};
+use crate::{Cycle, GB_HEIGHT, GB_WIDTH};
 use gilrs::Gilrs;
 use std::time::Duration;
 use winit_input_helper::WinitInputHelper;
 
 pub const SM83_CYCLE_TIME: Duration = Duration::from_nanos(1_000_000_000 / SM83_CLOCK_SPEED);
-pub const CYCLES_IN_FRAME: Cycle = Cycle::new(456 * 154); // 456 Cycles times 154 scanlines
+pub const CYCLES_IN_FRAME: Cycle = 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 {
-        Some(path) => SM83::boot_new(path)?,
-        None => SM83::new(),
-    };
+pub fn run_frame(emu: &mut Emulator, gamepad: &mut Gilrs, key: &WinitInputHelper) -> Cycle {
+    let mut elapsed = 0;
 
-    eprintln!("Initialized GB Emulator");
-
-    cpu.load_cartridge(rom_path)?;
-    Ok(cpu)
-}
-
-pub fn rom_title(game_boy: &SM83) -> &str {
-    game_boy.rom_title().unwrap_or(DEFAULT_TITLE)
-}
-
-pub fn run(
-    game_boy: &mut SM83,
-    gamepad: &mut Gilrs,
-    input: &WinitInputHelper,
-    target: Cycle,
-) -> Cycle {
-    let mut elapsed = Cycle::new(0);
-
-    while elapsed < target {
-        if GAMEPAD_ENABLED {
     if let Some(event) = gamepad.next_event() {
-                joypad::handle_gamepad_input(game_boy.joypad_mut(), event);
-            }
+        joypad::handle_gamepad_input(emu.joyp_mut(), event);
     }
 
-        joypad::handle_keyboard_input(game_boy.joypad_mut(), input);
-        elapsed += game_boy.step();
-    }
-
-    elapsed
-}
-
-pub fn run_frame(game_boy: &mut SM83, gamepad: &mut Gilrs, input: &WinitInputHelper) -> Cycle {
-    let mut elapsed = Cycle::new(0);
-
+    joypad::handle_keyboard_input(emu.joyp_mut(), key);
     while elapsed < CYCLES_IN_FRAME {
-        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);
-        elapsed += game_boy.step();
+        elapsed += emu.step();
     }
 
     elapsed
 }
 
-pub fn draw(ppu: &Ppu, frame: &mut [u8]) {
-    ppu.copy_to_gui(frame);
+pub fn draw_frame(emu: &Emulator, buf: &mut [u8; GB_HEIGHT * GB_WIDTH * 4]) {
+    buf.copy_from_slice(emu.cpu.bus().ppu.frame_buf());
+}
+
+pub struct Emulator {
+    cpu: Cpu,
+    timestamp: Cycle,
+}
+
+impl Emulator {
+    fn new(cpu: Cpu) -> Self {
+        Self {
+            cpu,
+            timestamp: Default::default(),
+        }
+    }
+
+    fn step(&mut self) -> Cycle {
+        self.cpu.step()
+    }
+
+    fn load_cart(&mut self, rom: Vec<u8>) {
+        self.cpu.bus_mut().load_cart(rom)
+    }
+
+    fn joyp_mut(&mut self) -> &mut Joypad {
+        &mut self.cpu.bus_mut().joypad
+    }
+
+    pub fn set_prod(&mut self, prod: SampleProducer<f32>) {
+        self.cpu.bus_mut().apu.attach_producer(prod)
+    }
+
+    pub fn title(&self) -> &str {
+        self.cpu.bus().cart_title().unwrap_or(DEFAULT_TITLE)
+    }
+}
+
+pub mod build {
+    use std::fs::File;
+    use std::io::{Read, Result};
+    use std::path::Path;
+
+    use crate::bus::BOOT_SIZE;
+    use crate::cpu::Cpu;
+
+    use super::Emulator;
+
+    #[derive(Debug, Default)]
+    pub struct EmulatorBuilder {
+        boot: Option<[u8; BOOT_SIZE]>,
+        cart: Option<Vec<u8>>,
+    }
+
+    impl EmulatorBuilder {
+        pub fn new() -> Self {
+            Default::default()
+        }
+
+        pub fn with_boot<P: AsRef<Path>>(mut self, path: P) -> Result<Self> {
+            let mut file = File::open(path.as_ref())?;
+
+            let mut buf = [0x00; BOOT_SIZE];
+            file.read_exact(&mut buf)?;
+
+            self.boot = Some(buf);
+            Ok(self)
+        }
+
+        pub fn with_cart<P: AsRef<Path>>(mut self, path: P) -> Result<Self> {
+            let mut file = File::open(path.as_ref())?;
+
+            let mut buf = Vec::new();
+            file.read_to_end(&mut buf)?;
+
+            self.cart = Some(buf);
+            Ok(self)
+        }
+
+        pub fn finish(mut self) -> Emulator {
+            let mut emu = Emulator::new(match self.boot {
+                Some(rom) => Cpu::with_boot(rom),
+                None => Cpu::without_boot(),
+            });
+
+            if let Some(rom) = self.cart.take() {
+                emu.load_cart(rom)
+            }
+
+            emu
+        }
+    }
 }

src/joypad.rs

@@ -120,49 +120,57 @@ pub fn handle_keyboard_input(pad: &mut Joypad, input: &WinitInputHelper) {
 
     if input.key_pressed(VirtualKeyCode::Down) {
         state.dpad_down.update(true, irq);
-    } else if input.key_released(VirtualKeyCode::Down) {
+    }
+    if input.key_released(VirtualKeyCode::Down) {
         state.dpad_down.update(false, irq);
     }
 
     if input.key_pressed(VirtualKeyCode::Up) {
         state.dpad_up.update(true, irq);
-    } else if input.key_released(VirtualKeyCode::Up) {
+    }
+    if input.key_released(VirtualKeyCode::Up) {
         state.dpad_up.update(false, irq);
     }
 
     if input.key_pressed(VirtualKeyCode::Left) {
         state.dpad_left.update(true, irq);
-    } else if input.key_released(VirtualKeyCode::Left) {
+    }
+    if input.key_released(VirtualKeyCode::Left) {
         state.dpad_left.update(false, irq);
     }
 
     if input.key_pressed(VirtualKeyCode::Right) {
         state.dpad_right.update(true, irq);
-    } else if input.key_released(VirtualKeyCode::Right) {
+    }
+    if input.key_released(VirtualKeyCode::Right) {
         state.dpad_right.update(false, irq);
     }
 
     if input.key_pressed(VirtualKeyCode::T) {
         state.start.update(true, irq);
-    } else if input.key_released(VirtualKeyCode::T) {
+    }
+    if input.key_released(VirtualKeyCode::T) {
         state.start.update(false, irq);
     }
 
     if input.key_pressed(VirtualKeyCode::Y) {
         state.select.update(true, irq);
-    } else if input.key_released(VirtualKeyCode::Y) {
+    }
+    if input.key_released(VirtualKeyCode::Y) {
         state.select.update(false, irq);
     }
 
     if input.key_pressed(VirtualKeyCode::Z) {
         state.south.update(true, irq);
-    } else if input.key_released(VirtualKeyCode::Z) {
+    }
+    if input.key_released(VirtualKeyCode::Z) {
         state.south.update(false, irq);
     }
 
     if input.key_pressed(VirtualKeyCode::X) {
         state.east.update(true, irq);
-    } else if input.key_released(VirtualKeyCode::X) {
+    }
+    if input.key_released(VirtualKeyCode::X) {
         state.east.update(false, irq);
     }
 }

src/lib.rs

@@ -1,5 +1,5 @@
 pub use apu::gen::AudioSPSC;
-pub use instruction::cycle::Cycle;
+pub type Cycle = u64;
 
 pub const GB_WIDTH: usize = 160;
 pub const GB_HEIGHT: usize = 144;

src/main.rs

@@ -1,17 +1,20 @@
+use std::convert::TryInto;
+
 use anyhow::{anyhow, Result};
 use clap::{crate_authors, crate_description, crate_name, crate_version, App, Arg};
+use gb::emu::build::EmulatorBuilder;
 use gb::{AudioSPSC, Cycle, GB_HEIGHT, GB_WIDTH};
 use gilrs::Gilrs;
 use pixels::{PixelsBuilder, SurfaceTexture};
 use rodio::{OutputStream, Sink};
-use std::time::{Duration, Instant};
-use winit::dpi::LogicalSize;
+use winit::dpi::{LogicalSize, PhysicalSize};
 use winit::event::{Event, VirtualKeyCode};
 use winit::event_loop::{ControlFlow, EventLoop};
 use winit::window::{Window, WindowBuilder};
 use winit_input_helper::WinitInputHelper;
 
-const WINDOW_SCALE: f64 = 2.0;
+const WINDOW_SCALE: usize = 3;
+const AUDIO_ENABLED: bool = false;
 
 fn main() -> Result<()> {
     let app = App::new(crate_name!())
@@ -38,13 +41,15 @@ fn main() -> Result<()> {
         )
         .get_matches();
 
-    let rom_path = m
-        .value_of("rom")
-        .expect("Required value 'rom' was provided");
+    let mut emu_build =
+        EmulatorBuilder::new().with_cart(m.value_of("rom").expect("ROM path provided"))?;
 
-    let mut game_boy =
-        gb::emu::init(m.value_of("boot"), rom_path).expect("Initialize DMG-01 Emulator");
-    let rom_title = gb::emu::rom_title(&game_boy);
+    if let Some(path) = m.value_of("boot") {
+        emu_build = emu_build.with_boot(path)?;
+    }
+
+    let mut emu = emu_build.finish();
+    let rom_title = emu.title();
 
     let mut gamepad = Gilrs::new().expect("Initialize Controller Support");
 
@@ -63,19 +68,25 @@ fn main() -> Result<()> {
     };
 
     // Initialize Audio
+    let (_stream, stream_handle) = OutputStream::try_default().expect("Initialized Audio");
+
+    if AUDIO_ENABLED {
         let spsc: AudioSPSC<f32> = Default::default();
         let (prod, cons) = spsc.init();
-    let (_stream, stream_handle) = OutputStream::try_default().expect("Initialized Audio");
-    let sink = Sink::try_new(&stream_handle)?;
-    sink.append(cons);
-    game_boy.apu_mut().set_producer(prod);
+        let sink = {
+            let s = Sink::try_new(&stream_handle)?;
+            s.append(cons);
+            s.set_volume(0.1);
+            s
+        };
+
+        emu.set_prod(prod);
 
         std::thread::spawn(move || {
             sink.sleep_until_end();
         });
+    }
 
-    let mut start = Instant::now();
-    let frame_time = Duration::from_secs_f64(1.0 / 60.0); // 60 Hz on Host
     let mut cycle_count: Cycle = Default::default();
 
     event_loop.run(move |event, _, control_flow| {
@@ -100,54 +111,34 @@ fn main() -> Result<()> {
                 pixels.resize_surface(size.width, size.height);
             }
 
-            let mut diff = Instant::now() - start;
-            while diff.subsec_nanos() < frame_time.subsec_nanos() {
-                if cycle_count < gb::emu::CYCLES_IN_FRAME {
-                    cycle_count += gb::emu::run_frame(&mut game_boy, &mut gamepad, &input);
-                }
-
-                diff = Instant::now() - start;
-            }
-            start = Instant::now();
+            cycle_count += gb::emu::run_frame(&mut emu, &mut gamepad, &input);
 
             if cycle_count >= gb::emu::CYCLES_IN_FRAME {
                 cycle_count %= gb::emu::CYCLES_IN_FRAME;
 
-                gb::emu::draw(game_boy.ppu(), pixels.get_frame());
+                let buf: &mut [u8; GB_WIDTH * GB_HEIGHT * 4] = pixels
+                    .get_frame()
+                    .try_into()
+                    .expect("Size of Pixel Buffer is GB_WIDTH * GB_HEIGHT * 4");
+
+                gb::emu::draw_frame(&emu, buf);
                 window.request_redraw();
             }
         }
     });
 }
 
-#[cfg(not(windows))]
 fn create_window(event_loop: &EventLoop<()>, title: &str) -> Result<Window> {
-    let size = LogicalSize::new((GB_WIDTH as f64) * SCALE, (GB_HEIGHT as f64) * SCALE);
-    Ok(WindowBuilder::new()
-        .with_title(title)
-        .with_inner_size(size)
-        .with_min_inner_size(size)
-        .with_resizable(true)
-        .with_decorations(true)
-        .with_transparent(false)
-        .build(event_loop)?)
-}
-
-#[cfg(windows)]
-fn create_window(event_loop: &EventLoop<()>, title: &str) -> Result<Window> {
-    use winit::platform::windows::WindowBuilderExtWindows;
-
-    let size = LogicalSize::new(
-        (GB_WIDTH as f64) * WINDOW_SCALE,
-        (GB_HEIGHT as f64) * WINDOW_SCALE,
+    let logical = LogicalSize::new(GB_WIDTH as f64, GB_HEIGHT as f64);
+    let physical = PhysicalSize::new(
+        (GB_WIDTH * WINDOW_SCALE) as f32,
+        (GB_HEIGHT * WINDOW_SCALE) as f32,
     );
+
     Ok(WindowBuilder::new()
         .with_title(title)
-        .with_inner_size(size)
-        .with_min_inner_size(size)
+        .with_min_inner_size(logical)
+        .with_inner_size(physical)
         .with_resizable(true)
-        .with_decorations(true)
-        .with_transparent(false)
-        .with_drag_and_drop(false)
         .build(event_loop)?)
 }

src/ppu.rs

@@ -1,5 +1,5 @@
 use crate::bus::BusIo;
-use crate::instruction::cycle::Cycle;
+use crate::Cycle;
 use crate::GB_HEIGHT;
 use crate::GB_WIDTH;
 use dma::DirectMemoryAccess;
@@ -70,7 +70,7 @@ impl BusIo for Ppu {
 }
 
 impl Ppu {
-    pub(crate) fn clock(&mut self) {
+    pub(crate) fn tick(&mut self) {
         self.cycle += 1;
 
         if !self.ctrl.lcd_enabled() {
@@ -79,7 +79,7 @@ impl Ppu {
 
         match self.stat.mode() {
             PpuMode::OamScan => {
-                if self.cycle >= 80.into() {
+                if self.cycle >= 80 {
                     self.stat.set_mode(PpuMode::Drawing);
                 }
 
@@ -88,7 +88,7 @@ impl Ppu {
             PpuMode::Drawing => {
                 if self.ctrl.lcd_enabled() {
                     // Only Draw when the LCD Is Enabled
-                    self.draw(self.cycle.into());
+                    self.draw(self.cycle);
                 } else {
                     self.reset();
                 }
@@ -125,7 +125,7 @@ impl Ppu {
             PpuMode::HBlank => {
                 // This mode will always end at 456 cycles
 
-                if self.cycle >= 456.into() {
+                if self.cycle >= 456 {
                     self.cycle %= 456;
                     self.pos.line_y += 1;
 
@@ -167,7 +167,7 @@ impl Ppu {
                 }
             }
             PpuMode::VBlank => {
-                if self.cycle > 456.into() {
+                if self.cycle > 456 {
                     self.cycle %= 456;
                     self.pos.line_y += 1;
 
@@ -228,23 +228,26 @@ impl Ppu {
         self.scan_state.next();
     }
 
-    fn draw(&mut self, _cycle: u32) {
+    fn draw(&mut self, _cycle: Cycle) {
         use FetcherState::*;
 
-        let iter = &mut self.obj_buffer.iter();
+        let mut iter = self.obj_buffer.iter_mut();
+        let default = &mut None;
 
         let obj_attr = loop {
-            match iter.flatten().next() {
-                Some(attr) => {
+            match iter.next() {
+                Some(attr_opt) => {
+                    if let Some(attr) = attr_opt {
                         if attr.x <= (self.x_pos + 8) {
                             self.fetch.back.reset();
                             self.fetch.back.pause();
                             self.fifo.pause();
 
-                        break Some(*attr);
+                            break attr_opt;
                         }
                     }
-                None => break None,
+                }
+                None => break default,
             }
         };
 
@@ -252,10 +255,10 @@ impl Ppu {
             match self.fetch.obj.state {
                 TileNumber => {
                     self.fetch.obj.tile.with_id(attr.tile_index);
-                    self.fetch.obj.next(ToLowByteSleep);
+                    self.fetch.obj.next(SleepOne);
                 }
-                ToLowByteSleep => self.fetch.obj.next(TileLowByte),
-                TileLowByte => {
+                SleepOne => self.fetch.obj.next(TileLow),
+                TileLow => {
                     let obj_size = self.ctrl.obj_size();
 
                     let addr = PixelFetcher::get_obj_addr(&attr, &self.pos, obj_size);
@@ -263,10 +266,10 @@ impl Ppu {
                     let byte = self.read_byte(addr);
                     self.fetch.obj.tile.with_low_byte(byte);
 
-                    self.fetch.obj.next(ToHighByteSleep);
+                    self.fetch.obj.next(SleepTwo);
                 }
-                ToHighByteSleep => self.fetch.obj.next(TileHighByte),
-                TileHighByte => {
+                SleepTwo => self.fetch.obj.next(TileHigh),
+                TileHigh => {
                     let obj_size = self.ctrl.obj_size();
 
                     let addr = PixelFetcher::get_obj_addr(&attr, &self.pos, obj_size);
@@ -274,10 +277,10 @@ impl Ppu {
                     let byte = self.read_byte(addr + 1);
                     self.fetch.obj.tile.with_high_byte(byte);
 
-                    self.fetch.obj.next(ToFifoSleep);
+                    self.fetch.obj.next(SleepThree);
                 }
-                ToFifoSleep => self.fetch.obj.next(SendToFifoOne),
-                SendToFifoOne => {
+                SleepThree => self.fetch.obj.next(ToFifoOne),
+                ToFifoOne => {
                     // Load into Fifo
                     let (high, low) = self
                         .fetch
@@ -289,13 +292,12 @@ impl Ppu {
                     let tbpp = Pixels::from_bytes(high, low);
 
                     let palette_kind = attr.flags.palette();
-
-                    let end = Pixels::PIXEL_COUNT - self.fifo.obj.len();
-                    let start = Pixels::PIXEL_COUNT - end;
-
                     let x_flip = attr.flags.x_flip();
 
-                    for i in start..Pixels::PIXEL_COUNT {
+                    let pixel_count = (attr.x - self.x_pos) as usize;
+                    let start = self.fifo.obj.len();
+
+                    for i in start..pixel_count {
                         let x = if x_flip { 7 - i } else { i };
 
                         let priority = attr.flags.priority();
@@ -312,11 +314,11 @@ impl Ppu {
 
                     self.fetch.back.resume();
                     self.fifo.resume();
-                    self.obj_buffer.remove(&attr);
+                    let _ = std::mem::take(obj_attr);
 
-                    self.fetch.obj.next(SendToFifoTwo);
+                    self.fetch.obj.next(ToFifoTwo);
                 }
-                SendToFifoTwo => self.fetch.obj.reset(),
+                ToFifoTwo => self.fetch.obj.reset(),
             }
         }
 
@@ -346,31 +348,31 @@ impl Ppu {
                     self.fetch.back.tile.with_id(id);
 
                     // Move on to the Next state in 2 T-cycles
-                    self.fetch.back.next(ToLowByteSleep);
+                    self.fetch.back.next(SleepOne);
                 }
-                ToLowByteSleep => self.fetch.back.next(TileLowByte),
-                TileLowByte => {
+                SleepOne => self.fetch.back.next(TileLow),
+                TileLow => {
                     let addr = self.fetch.bg_byte_addr(&self.ctrl, &self.pos);
 
                     let low = self.read_byte(addr);
                     self.fetch.back.tile.with_low_byte(low);
 
-                    self.fetch.back.next(ToHighByteSleep);
+                    self.fetch.back.next(SleepTwo);
                 }
-                ToHighByteSleep => self.fetch.back.next(TileHighByte),
-                TileHighByte => {
+                SleepTwo => self.fetch.back.next(TileHigh),
+                TileHigh => {
                     let addr = self.fetch.bg_byte_addr(&self.ctrl, &self.pos);
 
                     let high = self.read_byte(addr + 1);
                     self.fetch.back.tile.with_high_byte(high);
 
-                    self.fetch.back.next(ToFifoSleep);
+                    self.fetch.back.next(SleepThree);
                 }
-                ToFifoSleep => self.fetch.back.next(SendToFifoOne),
-                SendToFifoOne => {
-                    self.fetch.back.next(SendToFifoTwo);
+                SleepThree => self.fetch.back.next(ToFifoOne),
+                ToFifoOne => {
+                    self.fetch.back.next(ToFifoTwo);
                 }
-                SendToFifoTwo => {
+                ToFifoTwo => {
                     if let Ok(()) = self.fetch.send_to_fifo(&mut self.fifo) {
                         self.fetch.x_pos += 1;
                         self.fetch.back.next(TileNumber);
@@ -381,12 +383,12 @@ impl Ppu {
         }
 
         if self.fifo.is_enabled() {
-            if self.x_pos == 0 && !self.fifo.back.is_empty() && self.scanline_start {
+            if self.x_pos == 0 && self.scanline_start {
                 self.to_discard = self.pos.scroll_x % 8;
                 self.scanline_start = false;
             }
 
-            if self.to_discard > 0 {
+            if self.to_discard > 0 && !self.fifo.back.is_empty() {
                 let _ = self.fifo.back.pop_front();
                 self.to_discard -= 1;
 
@@ -416,8 +418,8 @@ impl Ppu {
         self.frame_buf.swap_with_slice(&mut blank);
     }
 
-    pub fn copy_to_gui(&self, frame: &mut [u8]) {
-        frame.copy_from_slice(self.frame_buf.as_ref());
+    pub(crate) fn frame_buf(&self) -> &[u8; GB_HEIGHT * GB_WIDTH * 4] {
+        &self.frame_buf
     }
 
     fn clock_fifo(&mut self) -> Option<GrayShade> {
@@ -468,7 +470,7 @@ impl Default for Ppu {
     fn default() -> Self {
         Self {
             vram: Box::new([0u8; VRAM_SIZE]),
-            cycle: Cycle::new(0),
+            cycle: Default::default(),
             frame_buf: Box::new([0; GB_WIDTH * GB_HEIGHT * 4]),
             int: Default::default(),
             ctrl: Default::default(),
@@ -608,67 +610,34 @@ impl<'a> From<&'a [u8; 4]> for ObjectAttribute {
 
 #[derive(Debug)]
 struct ObjectBuffer {
-    buf: [Option<ObjectAttribute>; OBJECT_LIMIT],
+    inner: [Option<ObjectAttribute>; OBJECT_LIMIT],
     len: usize,
 }
 
-impl ObjectBuffer {
-    fn iter(&self) -> std::slice::Iter<'_, Option<ObjectAttribute>> {
-        self.into_iter()
-    }
-}
-
-impl<'a> IntoIterator for &'a ObjectBuffer {
-    type Item = &'a Option<ObjectAttribute>;
-
-    type IntoIter = std::slice::Iter<'a, Option<ObjectAttribute>>;
-
-    fn into_iter(self) -> Self::IntoIter {
-        self.buf.iter()
-    }
-}
-
-impl<'a> IntoIterator for &'a mut ObjectBuffer {
-    type Item = &'a Option<ObjectAttribute>;
-
-    type IntoIter = std::slice::Iter<'a, Option<ObjectAttribute>>;
-
-    fn into_iter(self) -> Self::IntoIter {
-        self.buf.iter()
-    }
-}
-
 impl ObjectBuffer {
     fn is_full(&self) -> bool {
         self.len == OBJECT_LIMIT
     }
 
     fn clear(&mut self) {
-        self.buf = [Default::default(); 10];
+        self.inner = [Default::default(); 10];
         self.len = 0;
     }
 
     fn add(&mut self, attr: ObjectAttribute) {
-        self.buf[self.len] = Some(attr);
+        self.inner[self.len] = Some(attr);
         self.len += 1;
     }
 
-    fn remove(&mut self, attr: &ObjectAttribute) {
-        let maybe_index = self.buf.iter().position(|maybe_attr| match maybe_attr {
-            Some(other_attr) => attr == other_attr,
-            None => false,
-        });
-
-        if let Some(i) = maybe_index {
-            self.buf[i] = None;
-        }
+    fn iter_mut(&mut self) -> std::slice::IterMut<'_, Option<ObjectAttribute>> {
+        self.inner.iter_mut()
     }
 }
 
 impl Default for ObjectBuffer {
     fn default() -> Self {
         Self {
-            buf: [Default::default(); OBJECT_LIMIT],
+            inner: [Default::default(); OBJECT_LIMIT],
             len: Default::default(),
         }
     }
@@ -903,13 +872,13 @@ impl WindowLineCounter {
 #[derive(Debug, Clone, Copy)]
 enum FetcherState {
     TileNumber,
-    ToLowByteSleep,
-    TileLowByte,
-    ToHighByteSleep,
-    TileHighByte,
-    ToFifoSleep,
-    SendToFifoOne,
-    SendToFifoTwo,
+    SleepOne,
+    TileLow,
+    SleepTwo,
+    TileHigh,
+    SleepThree,
+    ToFifoOne,
+    ToFifoTwo,
 }
 
 impl Default for FetcherState {

src/ppu/dma.rs

@@ -1,4 +1,4 @@
-use crate::instruction::cycle::Cycle;
+use crate::Cycle;
 
 #[derive(Debug, Default)]
 pub(crate) struct DirectMemoryAccess {
@@ -9,7 +9,7 @@ pub(crate) struct DirectMemoryAccess {
 }
 
 impl DirectMemoryAccess {
-    pub(crate) fn clock(&mut self) -> Option<(u16, u16)> {
+    pub(crate) fn tick(&mut self) -> Option<(u16, u16)> {
         match self.state {
             DmaState::Pending => {
                 self.cycle += 1;
@@ -56,7 +56,7 @@ impl DirectMemoryAccess {
     }
 
     fn reset(&mut self) {
-        self.cycle = Cycle::new(0);
+        self.cycle = 0;
         self.state = DmaState::Disabled;
         self.start.0 = None;
     }

src/scheduler.rs

@@ -0,0 +1,79 @@
+use crate::Cycle;
+use std::collections::BinaryHeap;
+
+#[derive(Debug)]
+pub(crate) struct Scheduler {
+    timestamp: Cycle,
+    queue: BinaryHeap<Event>,
+}
+
+impl Scheduler {
+    pub(crate) fn init() -> Self {
+        let mut scheduler = Self {
+            timestamp: Default::default(),
+            queue: Default::default(),
+        };
+
+        scheduler.push(Event {
+            kind: EventKind::TimestampOverflow,
+            timestamp: Cycle::MAX,
+            cb: |_delay| panic!("Reached Cycle::MAX"),
+        });
+
+        scheduler
+    }
+
+    pub(crate) fn push(&mut self, event: Event) {
+        self.queue.push(event);
+    }
+
+    pub(crate) fn step(&mut self, cycles: Cycle) {
+        self.timestamp += cycles;
+
+        loop {
+            let should_pop = match self.queue.peek() {
+                Some(event) => self.timestamp >= event.timestamp,
+                None => false,
+            };
+
+            if !should_pop {
+                break;
+            }
+
+            let event = self.queue.pop().expect("Pop Event from Scheduler Queue");
+
+            (event.cb)(self.timestamp - event.timestamp);
+        }
+    }
+}
+
+#[derive(Debug)]
+pub(crate) struct Event {
+    kind: EventKind,
+    cb: fn(Cycle),
+    pub(crate) timestamp: Cycle,
+}
+
+impl Eq for Event {}
+impl PartialEq for Event {
+    fn eq(&self, other: &Self) -> bool {
+        self.kind == other.kind && self.timestamp == other.timestamp
+    }
+}
+
+impl PartialOrd for Event {
+    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl Ord for Event {
+    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
+        self.timestamp.cmp(&other.timestamp)
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(crate) enum EventKind {
+    TimestampOverflow,
+}

src/timer.rs

@@ -5,19 +5,33 @@ pub(crate) struct Timer {
     /// 0xFF07 | TAC - Timer Control
     pub(crate) ctrl: TimerControl,
     /// 0xFF05 | TIMA - Timer Counter
-    pub(crate) counter: u8,
+    counter: u8,
     /// 0xFF06 | TMA - Timer Modulo
     pub(crate) modulo: u8,
     /// 0xFF04 | DIV - Divider Register
     pub(crate) divider: u16,
-    prev_and_result: Option<u8>,
+
+    and_result: Option<u8>,
     interrupt: bool,
+    state: State,
 }
 
 impl Timer {
-    pub(crate) fn clock(&mut self) {
+    pub(crate) fn tick(&mut self) {
+        use State::*;
         use TimerSpeed::*;
 
+        match self.state {
+            TIMAOverflow(_) | AbortedTIMAOverflow(_) => self.next(),
+            LoadTMA => {
+                self.counter = self.modulo;
+                self.interrupt = true;
+
+                self.next();
+            }
+            Normal => {}
+        }
+
         self.divider = self.divider.wrapping_add(1);
 
         // Get Bit Position
@@ -29,27 +43,34 @@ impl Timer {
         };
 
         let bit = (self.divider >> bit) as u8 & 0x01;
-        let timer_enable = self.ctrl.enabled() as u8;
-        let and_result = bit & timer_enable;
+        let new_result = bit & self.ctrl.enabled() as u8;
 
-        if let Some(0x01) = self.prev_and_result {
-            if and_result == 0x00 {
+        if let Some(0x01) = self.and_result {
+            if new_result == 0x00 {
                 // Falling Edge, increase TIMA Register
-                self.increment_tima();
+                self.inc_counter();
             }
         }
 
-        self.prev_and_result = Some(and_result);
+        self.and_result = Some(new_result);
     }
 
-    fn increment_tima(&mut self) {
-        let (result, did_overflow) = self.counter.overflowing_add(1);
+    /// 0xFF05 | TIMA - Timer Counter
+    pub(crate) fn tima(&self) -> u8 {
+        self.counter
+    }
 
-        self.counter = if did_overflow {
-            self.interrupt = true;
-            self.modulo
-        } else {
-            result
+    /// 0xFF05 | TIMA - Timer Counter
+    pub(crate) fn set_tima(&mut self, byte: u8) {
+        use State::*;
+
+        match self.state {
+            Normal | AbortedTIMAOverflow(_) => self.counter = byte,
+            TIMAOverflow(step) => {
+                self.counter = byte;
+                self.state = AbortedTIMAOverflow(step);
+            }
+            LoadTMA => {}
         }
     }
 
@@ -60,6 +81,27 @@ impl Timer {
     pub(crate) fn set_interrupt(&mut self, value: bool) {
         self.interrupt = value;
     }
+
+    fn inc_counter(&mut self) {
+        let (sum, did_overflow) = self.counter.overflowing_add(1);
+        self.counter = if did_overflow { 0 } else { sum };
+
+        if did_overflow {
+            self.state = State::TIMAOverflow(0);
+        }
+    }
+
+    fn next(&mut self) {
+        use State::*;
+
+        self.state = match self.state {
+            Normal | LoadTMA => Normal,
+            AbortedTIMAOverflow(4) => Normal,
+            TIMAOverflow(4) => LoadTMA,
+            AbortedTIMAOverflow(step) => AbortedTIMAOverflow(step + 1),
+            TIMAOverflow(step) => TIMAOverflow(step + 1),
+        }
+    }
 }
 
 impl Default for Timer {
@@ -70,7 +112,8 @@ impl Default for Timer {
             modulo: 0,
             divider: 0,
             interrupt: false,
-            prev_and_result: None,
+            and_result: None,
+            state: State::Normal,
         }
     }
 }
@@ -132,3 +175,11 @@ impl From<TimerControl> for u8 {
         ctrl.0
     }
 }
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum State {
+    TIMAOverflow(u8),
+    AbortedTIMAOverflow(u8),
+    Normal,
+    LoadTMA,
+}

src/work_ram.rs

@@ -28,48 +28,25 @@ impl Default for WorkRam {
     }
 }
 
-#[derive(Debug, Clone, Copy)]
-enum BankNumber {
-    One = 1,
-    Two = 2,
-    Three = 3,
-    Four = 4,
-    Five = 5,
-    Six = 6,
-    Seven = 7,
-}
-
 #[derive(Debug)]
 pub(crate) struct VariableWorkRam {
-    current: BankNumber,
-    bank_n: Box<[[u8; VARIABLE_WORK_RAM_SIZE]; 7]>, // 4K for Variable amount of Banks (Banks 1 -> 7) in Game Boy Colour
+    buf: Box<[u8; VARIABLE_WORK_RAM_SIZE]>, // 4K for Variable amount of Banks (Banks 1 -> 7) in Game Boy Colour
 }
 
 impl Default for VariableWorkRam {
     fn default() -> Self {
         Self {
-            current: BankNumber::One,
-            bank_n: Box::new([[0u8; VARIABLE_WORK_RAM_SIZE]; 7]),
+            buf: Box::new([0u8; VARIABLE_WORK_RAM_SIZE]),
         }
     }
 }
 
-impl VariableWorkRam {
-    fn set_current_bank(&mut self, bank: BankNumber) {
-        self.current = bank;
-    }
-
-    fn get_current_bank(&self) -> &BankNumber {
-        &self.current
-    }
-}
-
 impl BusIo for VariableWorkRam {
     fn write_byte(&mut self, addr: u16, byte: u8) {
-        self.bank_n[self.current as usize][addr as usize - VARIABLE_WORK_RAM_START_ADDRESS] = byte;
+        self.buf[addr as usize - VARIABLE_WORK_RAM_START_ADDRESS] = byte;
     }
 
     fn read_byte(&self, addr: u16) -> u8 {
-        self.bank_n[self.current as usize][addr as usize - VARIABLE_WORK_RAM_START_ADDRESS]
+        self.buf[addr as usize - VARIABLE_WORK_RAM_START_ADDRESS]
     }
 }