fix(apu): increase accuracy of apu emulation
Reintroduce the Frame Sequencer and it's state enum (needed so that we can reset the FS on NR52 enable)
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75
src/apu.rs
75
src/apu.rs
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@ -5,6 +5,7 @@ use types::ch1::{Sweep, SweepDirection};
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use types::ch3::Volume as Ch3Volume;
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use types::ch4::{CounterWidth, Frequency as Ch4Frequency, PolynomialCounter};
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use types::common::{EnvelopeDirection, FrequencyHigh, SoundDuty, VolumeEnvelope};
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use types::fs::{FrameSequencer, FrameSequencerState};
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use types::{ChannelControl, SoundOutput};
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pub mod gen;
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@ -25,7 +26,7 @@ pub struct Apu {
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/// Noise
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ch4: Channel4,
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// Frame Sequencer
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sequencer: FrameSequencer,
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div_prev: Option<u16>,
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prod: Option<SampleProducer<f32>>,
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@ -42,7 +43,7 @@ impl BusIo for Apu {
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0x16 => self.ch2.duty(),
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0x17 => self.ch2.envelope(),
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0x19 => self.ch2.freq_hi(),
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0x1A => self.ch3.enabled(),
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0x1A => self.ch3.dac_enabled(),
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0x1C => self.ch3.volume(),
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0x1E => self.ch3.freq_hi(),
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0x21 => self.ch4.envelope(),
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@ -70,7 +71,7 @@ impl BusIo for Apu {
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0x17 if self.ctrl.enabled => self.ch2.set_envelope(byte),
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0x18 if self.ctrl.enabled => self.ch2.set_freq_lo(byte),
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0x19 if self.ctrl.enabled => self.ch2.set_freq_hi(byte),
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0x1A if self.ctrl.enabled => self.ch3.set_enabled(byte),
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0x1A if self.ctrl.enabled => self.ch3.set_dac_enabled(byte),
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0x1B if self.ctrl.enabled => self.ch3.set_len(byte),
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0x1C if self.ctrl.enabled => self.ch3.set_volume(byte),
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0x1D if self.ctrl.enabled => self.ch3.set_freq_lo(byte),
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@ -96,19 +97,21 @@ impl Apu {
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pub(crate) fn tick(&mut self, div: u16) {
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self.sample_counter += SAMPLE_INCREMENT;
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// Length Control (256Hz)
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if self.falling_edge(13, div) {
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self.handle_length();
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}
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// Frame Sequencer (512Hz)
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if self.falling_edge(12, div) {
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use FrameSequencerState::*;
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// Sweep (128Hz)
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if self.falling_edge(14, div) {
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self.handle_sweep();
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}
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self.sequencer.next();
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// Volume Envelope (64Hz)
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if self.falling_edge(15, div) {
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self.handle_volume();
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match self.sequencer.state() {
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Length => self.handle_length(),
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LengthAndSweep => {
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self.handle_length();
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self.handle_sweep();
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}
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Envelope => self.handle_envelope(),
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Nothing => {}
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}
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}
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self.div_prev = Some(div);
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@ -164,13 +167,14 @@ impl Apu {
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if self.ctrl.enabled {
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// Frame Sequencer reset to Step 0
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// TODO: With the current implementation of the frame sequencer, what does this even mean?
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self.sequencer.reset();
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// Square Duty units are reset to first step
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self.ch1.duty_pos = 0;
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self.ch2.duty_pos = 0;
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// Wave Channel's sample buffer reset to 0
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self.ch3.offset = 0;
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}
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if !self.ctrl.enabled {
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@ -191,7 +195,7 @@ impl Apu {
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self.ch2.freq_lo = Default::default();
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self.ch2.freq_hi = Default::default();
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self.ch3.enabled = Default::default();
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self.ch3.dac_enabled = Default::default();
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self.ch3.len = Default::default();
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self.ch3.volume = Default::default();
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self.ch3.freq_lo = Default::default();
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@ -205,9 +209,10 @@ impl Apu {
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self.ctrl.channel = Default::default();
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self.ctrl.output = Default::default();
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// Disable the rest of the channels
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// Disable the Channels
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self.ch1.enabled = Default::default();
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self.ch2.enabled = Default::default();
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self.ch3.enabled = Default::default();
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self.ch4.enabled = Default::default();
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}
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@ -303,7 +308,7 @@ impl Apu {
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}
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}
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fn handle_volume(&mut self) {
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fn handle_envelope(&mut self) {
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// Channels 1, 2 and 4 have Volume Envelopes
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Self::clock_envelope(
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@ -505,7 +510,9 @@ impl Channel1 {
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self.length_timer = 64;
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}
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self.enabled = true;
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if self.is_dac_enabled() {
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self.enabled = true;
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}
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}
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}
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@ -636,7 +643,9 @@ impl Channel2 {
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self.length_timer = 64;
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}
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self.enabled = true;
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if self.is_dac_enabled() {
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self.enabled = true;
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}
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}
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}
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@ -652,7 +661,7 @@ impl Channel2 {
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#[derive(Debug, Default)]
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pub(crate) struct Channel3 {
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/// 0xFF1A | NR30 - Channel 3 Sound on/off
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enabled: bool,
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dac_enabled: bool,
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/// 0xFF1B | NR31 - Sound Length
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len: u8,
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/// 0xFF1C | NR32 - Channel 3 Volume
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@ -669,6 +678,8 @@ pub(crate) struct Channel3 {
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freq_timer: u16,
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offset: u8,
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enabled: bool,
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}
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impl BusIo for Channel3 {
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@ -693,13 +704,17 @@ impl Channel3 {
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const WAVE_RAM_START_ADDR: u16 = 0xFF30;
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/// 0xFF1A | NR30 - Channel 3 Sound on/off
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pub(crate) fn enabled(&self) -> u8 {
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((self.enabled as u8) << 7) | 0x7F
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pub(crate) fn dac_enabled(&self) -> u8 {
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((self.dac_enabled as u8) << 7) | 0x7F
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}
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/// 0xFF1A | NR30 - Channel 3 Sound on/off
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pub(crate) fn set_enabled(&mut self, byte: u8) {
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self.enabled = (byte >> 7) & 0x01 == 0x01;
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pub(crate) fn set_dac_enabled(&mut self, byte: u8) {
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self.dac_enabled = (byte >> 7) & 0x01 == 0x01;
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if !self.dac_enabled {
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self.enabled = false;
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}
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}
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/// 0xFF1B | NR31 - Sound Length
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@ -746,12 +761,14 @@ impl Channel3 {
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self.length_timer = 256;
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}
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self.enabled = true;
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if self.dac_enabled {
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self.enabled = true;
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}
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}
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}
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fn amplitude(&self) -> f32 {
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if self.enabled {
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if self.dac_enabled && self.enabled {
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let input = self.read_sample(self.offset) >> self.volume.shift_count();
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(input as f32 / 7.5) - 1.0
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} else {
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@ -866,7 +883,9 @@ impl Channel4 {
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// LFSR behaviour during trigger event
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self.lf_shift = 0x7FFF;
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self.enabled = true;
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if self.is_dac_enabled() {
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self.enabled = true;
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}
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}
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}
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@ -73,7 +73,7 @@ pub(crate) mod ch1 {
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}
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}
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pub(crate) mod ch3 {
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pub(super) mod ch3 {
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#[derive(Debug, Clone, Copy)]
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pub(crate) enum Volume {
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Mute = 0,
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@ -102,7 +102,7 @@ pub(crate) mod ch3 {
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}
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}
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pub(crate) mod ch4 {
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pub(super) mod ch4 {
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use super::bitfield;
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bitfield! {
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@ -217,7 +217,7 @@ pub(crate) mod ch4 {
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}
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}
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pub(crate) mod common {
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pub(super) mod common {
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use super::bitfield;
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bitfield! {
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@ -508,3 +508,56 @@ impl From<ChannelControl> for u8 {
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ctrl.0
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}
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}
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pub(super) mod fs {
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#[derive(Debug)]
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pub(crate) struct FrameSequencer {
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step: u8,
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state: FrameSequencerState,
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}
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impl Default for FrameSequencer {
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fn default() -> Self {
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Self {
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step: Default::default(),
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state: FrameSequencerState::Length,
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}
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}
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}
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impl FrameSequencer {
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pub(crate) fn next(&mut self) {
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use FrameSequencerState::*;
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self.step = (self.step + 1) % 8;
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self.state = match self.step {
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0 => Length,
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1 => Nothing,
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2 => LengthAndSweep,
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3 => Nothing,
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4 => Length,
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5 => Nothing,
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6 => LengthAndSweep,
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7 => Envelope,
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_ => unreachable!("Step {} is invalid for the Frame Sequencer", self.step),
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};
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}
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pub(crate) fn state(&self) -> FrameSequencerState {
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self.state
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}
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pub(crate) fn reset(&mut self) {
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self.step = Default::default();
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self.state = FrameSequencerState::Length;
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}
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}
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#[derive(Debug, Clone, Copy)]
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pub(crate) enum FrameSequencerState {
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Length,
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Nothing,
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LengthAndSweep,
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Envelope,
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}
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}
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