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fix(apu): increase accuracy of apu emulation

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Reintroduce the Frame Sequencer and it's state enum (needed so that we
can reset the FS on NR52 enable)
This commit is contained in:
Rekai Nyangadzayi Musuka
2021-08-17 22:18:40 -05:00
parent 8fea8eb1ff
commit 22f96a10e7
2 changed files with 103 additions and 31 deletions
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75
src/apu.rs
View File

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

59
src/apu/types.rs
View File

@@ -73,7 +73,7 @@ pub(crate) mod ch1 {
}
}
pub(crate) mod ch3 {
pub(super) mod ch3 {
#[derive(Debug, Clone, Copy)]
pub(crate) enum Volume {
Mute = 0,
@@ -102,7 +102,7 @@ pub(crate) mod ch3 {
}
}
pub(crate) mod ch4 {
pub(super) mod ch4 {
use super::bitfield;
bitfield! {
@@ -217,7 +217,7 @@ pub(crate) mod ch4 {
}
}
pub(crate) mod common {
pub(super) mod common {
use super::bitfield;
bitfield! {
@@ -508,3 +508,56 @@ impl From<ChannelControl> for u8 {
ctrl.0
}
}
pub(super) mod fs {
#[derive(Debug)]
pub(crate) struct FrameSequencer {
step: u8,
state: FrameSequencerState,
}
impl Default for FrameSequencer {
fn default() -> Self {
Self {
step: Default::default(),
state: FrameSequencerState::Length,
}
}
}
impl FrameSequencer {
pub(crate) fn next(&mut self) {
use FrameSequencerState::*;
self.step = (self.step + 1) % 8;
self.state = match self.step {
0 => Length,
1 => Nothing,
2 => LengthAndSweep,
3 => Nothing,
4 => Length,
5 => Nothing,
6 => LengthAndSweep,
7 => Envelope,
_ => unreachable!("Step {} is invalid for the Frame Sequencer", self.step),
};
}
pub(crate) fn state(&self) -> FrameSequencerState {
self.state
}
pub(crate) fn reset(&mut self) {
self.step = Default::default();
self.state = FrameSequencerState::Length;
}
}
#[derive(Debug, Clone, Copy)]
pub(crate) enum FrameSequencerState {
Length,
Nothing,
LengthAndSweep,
Envelope,
}
}