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More sound chip tidying
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@mattgodbolt
mattgodbolt committed Dec 31, 2024
1 parent 6463942 commit 0e8954a
Showing 1 changed file with 67 additions and 70 deletions.
137 changes: 67 additions & 70 deletions src/soundchip.js
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Original file line number Diff line number Diff line change
@@ -1,10 +1,29 @@
const FloatType = typeof Float64Array !== "undefined" ? Float64Array : Float32Array;

const volumeTable = new FloatType(16);
(() => {
let f = 1.0;
for (let i = 0; i < 15; ++i) {
volumeTable[i] = f / 4; // Bakes in the per channel volume
f *= Math.pow(10, -0.1);
}
volumeTable[15] = 0;
})();

function makeSineTable(attenuation) {
const sineTable = new FloatType(8192);
for (let i = 0; i < sineTable.length; ++i) {
sineTable[i] = Math.sin((2 * Math.PI * i) / sineTable.length) * attenuation;
}
return sineTable;
}

export class SoundChip {
constructor(sampleRate) {
this.cpuFreq = 1 / (2 * 1000 * 1000); // TODO hacky here
// 4MHz input signal. Internal divide-by-8
this.soundchipFreq = 4000000.0 / 8;
// Square wave changes every time a counter hits zero. Thus a full wave
// needs to be 2x counter zeros.
// Square wave changes every time a counter hits zero: A full wave needs to be 2x counter zeros.
this.waveDecrementPerSecond = this.soundchipFreq / 2;
// Each sample in the buffer represents (1/sampleRate) time, so each time
// we generate a sample, we need to decrement the counters by this amount:
Expand All @@ -13,32 +32,19 @@ export class SoundChip {
this.samplesPerCycle = sampleRate * this.cpuFreq;
this.minCyclesWELow = 14; // Somewhat empirically derived; Repton 2 has only 14 cycles between WE low and WE high (@0x2caa)

this.registers = [0, 0, 0, 0];
this.counter = [0, 0, 0, 0];
this.registers = new Uint16Array(4);
this.counter = new FloatType(4);
this.outputBit = [false, false, false, false];
this.volume = [0, 0, 0, 0];
this.generators = [];
for (let i = 0; i < 3; ++i) {
this.generators[i] = this.toneChannel.bind(this);
}
this.generators[3] = this.noiseChannel.bind(this);
this.generators[4] = this.sineChannel.bind(this);

this.volumeTable = [];
let f = 1.0;
for (let i = 0; i < 16; ++i) {
this.volumeTable[i] = f / this.generators.length; // Bakes in the per channel volume
f *= Math.pow(10, -0.1);
}
this.volumeTable[15] = 0;

const floatType = typeof Float64Array !== "undefined" ? Float64Array : Float32Array;

this.sineTable = new floatType(8192);

for (let i = 0; i < this.sineTable.length; ++i) {
this.sineTable[i] = Math.sin((2 * Math.PI * i) / this.sineTable.length) / this.generators.length;
}
this.volume = new FloatType(4);
this.generators = [
this.toneChannel.bind(this),
this.toneChannel.bind(this),
this.toneChannel.bind(this),
this.noiseChannel.bind(this),
this.sineChannel.bind(this),
];

this.sineTable = makeSineTable(1 / this.generators.length);
this.sineStep = 0;
this.sineOn = false;
this.sineTime = 0;
Expand All @@ -53,8 +59,7 @@ export class SoundChip {

this.residual = 0;
this.position = 0;
this.maxBufferSize = 4096;
this.buffer = new floatType(this.maxBufferSize);
this.buffer = new FloatType(4096);

this.latchedRegister = 0;
this.slowDataBus = 0;
Expand All @@ -74,27 +79,32 @@ export class SoundChip {
}

sineChannel(channel, out, offset, length) {
if (!this.sineOn) {
return;
}
if (!this.sineOn) return;

for (let i = 0; i < length; ++i) {
out[i + offset] += this.sineTable[this.sineTime & (this.sineTable.length - 1)];
this.sineTime += this.sineStep;
}
while (this.sineTime > this.sineTable.length) this.sineTime -= this.sineTable.length;
}

_doChannelStep(channel, addAmount) {
const newValue = this.counter[channel] - this.sampleDecrement;
if (newValue < 0) {
this.counter[channel] = Math.max(0, newValue + addAmount);
this.outputBit[channel] = !this.outputBit[channel];
return this.outputBit[channel];
} else {
this.counter[channel] = newValue;
return false;
}
}

toneChannel(channel, out, offset, length) {
let reg = this.registers[channel];
const reg = this.registers[channel] === 0 ? 1024 : this.registers[channel];
const vol = this.volume[channel];
if (reg === 0) reg = 1024;
for (let i = 0; i < length; ++i) {
this.counter[channel] -= this.sampleDecrement;
if (this.counter[channel] < 0) {
this.counter[channel] += reg;
if (this.counter[channel] < 0) this.counter[channel] = 0;
this.outputBit[channel] = !this.outputBit[channel];
}
this._doChannelStep(channel, reg);
out[i + offset] += this.outputBit[channel] * vol;
}
}
Expand Down Expand Up @@ -133,13 +143,7 @@ export class SoundChip {
const add = this.addFor(channel),
vol = this.volume[channel];
for (let i = 0; i < length; ++i) {
this.counter[channel] -= this.sampleDecrement;
if (this.counter[channel] < 0) {
this.counter[channel] += add;
if (this.counter[channel] < 0) this.counter[channel] = 0;
this.outputBit[channel] = !this.outputBit[channel];
if (this.outputBit[channel]) this.shiftLfsr();
}
if (this._doChannelStep(channel, add)) this.shiftLfsr();
out[i + offset] += (this.lfsr & 1) * vol;
}
}
Expand All @@ -150,10 +154,10 @@ export class SoundChip {
this.registers[1] = c1 & 0xffffff;
this.registers[2] = c2 & 0xffffff;
this.registers[3] = c3 & 0xffffff;
this.volume[0] = this.volumeTable[v0];
this.volume[1] = this.volumeTable[v1];
this.volume[2] = this.volumeTable[v2];
this.volume[3] = this.volumeTable[v3];
this.volume[0] = volumeTable[v0];
this.volume[1] = volumeTable[v1];
this.volume[2] = volumeTable[v2];
this.volume[3] = volumeTable[v3];
this.noisePoked();
}

Expand All @@ -171,22 +175,16 @@ export class SoundChip {

catchUp() {
const cyclesPending = this.scheduler.epoch - this.lastRunEpoch;
if (cyclesPending > 0) {
this.advance(cyclesPending);
}
if (cyclesPending > 0) this.advance(cyclesPending);
this.lastRunEpoch = this.scheduler.epoch;
}

setScheduler(scheduler_) {
this.scheduler = scheduler_;
this.lastRunEpoch = this.scheduler.epoch;
this.activeTask = this.scheduler.newTask(
function () {
if (this.active) {
this.poke(this.slowDataBus);
}
}.bind(this),
);
this.activeTask = this.scheduler.newTask(() => {
if (this.active) this.poke(this.slowDataBus);
});
}

render(out, offset, length) {
Expand All @@ -210,8 +208,8 @@ export class SoundChip {
const num = time * this.samplesPerCycle + this.residual;
let rounded = num | 0;
this.residual = num - rounded;
if (this.position + rounded >= this.maxBufferSize) {
rounded = this.maxBufferSize - this.position;
if (this.position + rounded >= this.buffer.length) {
rounded = this.buffer.length - this.position;
}
if (rounded === 0) return;
this.generate(this.buffer, this.position, rounded);
Expand All @@ -233,7 +231,7 @@ export class SoundChip {
if (command & 0x10) {
// Volume setting
const newVolume = value & 0x0f;
this.volume[channel] = this.volumeTable[newVolume];
this.volume[channel] = volumeTable[newVolume];
} else if (channel === 3) {
// For noise channel we always update the bottom bits.
this.registers[channel] = value & 0x0f;
Expand All @@ -250,11 +248,9 @@ export class SoundChip {
updateSlowDataBus(slowDataBus, active) {
this.slowDataBus = slowDataBus;
this.active = active;
// TODO: this probably isn't modeled correctly. Currently the
// sound chip "notices" a new data bus value some fixed number of
// cycles after WE (write enable) is triggered.
// In reality, the sound chip likely pulls data off the bus at a
// fixed point in its cycle, iff WE is active.
// TODO: this probably isn't modeled correctly. Currently the sound chip "notices" a new data bus value some
// fixed number of cycles after WE (write enable) is triggered. In reality, the sound chip likely pulls data off
// the bus at a fixed point in its cycle, iff WE is active.
if (active) {
this.activeTask.ensureScheduled(true, this.minCyclesWELow);
}
Expand All @@ -265,7 +261,8 @@ export class SoundChip {
for (let i = 0; i < 4; ++i) {
this.counter[i] = 0;
this.registers[i] = 0;
this.volume[i] = this.volumeTable[8]; // Real hardware would be volumeTable[0] but that's really quite loud and surprising...
// Real hardware would be volumeTable[0] but that's really quite loud and surprising...
this.volume[i] = volumeTable[8];
}
this.noisePoked();
this.advance(100000);
Expand Down

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