Press n or j to go to the next uncovered block, b, p or k for the previous block.
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import { ungzip } from "./archive.js";
import { hexword } from "./hex.js";
function secsToClocks(secs, cpuSpeed) {
return (cpuSpeed * secs) | 0;
}
// Atom tape encoding: wavebits sent one per poll via receiveBit().
// '0' bit = 4 cycles at 1200 Hz (toggle every 2 wavebits).
// '1' bit = 8 cycles at 2400 Hz (toggle every 1 wavebit).
// Carrier = continuous '1' bits.
function parityOf(curByte) {
let parity = false;
while (curByte) {
parity = !parity;
curByte >>>= 1;
}
return parity;
}
const ParityN = "N".charCodeAt(0);
class UefTape {
constructor(stream, model) {
this.stream = stream;
this.baseFrequency = 1200;
this.isAtom = model.isAtom;
this.cpuSpeed = model.cyclesPerSecond;
this.rewind();
}
get name() {
return this.stream.name;
}
/** @returns {Number} how far through the image the head is, 0 to 1 */
get position() {
const chunk = this.curChunk?.stream;
const chunkLeft = chunk ? chunk.end - chunk.pos : 0;
return (this.stream.pos - chunkLeft) / this.stream.end;
}
rewind() {
this.dummyData = [false, false, true, false, true, false, true, false, true, true];
this.state = -1;
this.count = 0;
this.curByte = 0;
this.numDataBits = 8;
this.parity = ParityN;
this.numParityBits = 0;
this.numStopBits = 1;
this.carrierBefore = 0;
this.carrierAfter = 0;
this.shortWave = 0;
this.atomPhase = 0;
this.atomSubCount = 0;
this.atomWavebitsLeft = 0;
this.atomToggleEvery = 1;
this.stream.seek(10);
const minor = this.stream.readByte();
const major = this.stream.readByte();
if (major !== 0x00) throw "Unsupported UEF version " + major + "." + minor;
// No chunk yet: the first poll reads one. null, later, means the tape has run off the end.
this.curChunk = undefined;
}
readChunk() {
const chunkId = this.stream.readInt16();
const length = this.stream.readInt32();
return {
id: chunkId,
stream: this.stream.substream(length),
};
}
// On BBC, acia is the ACIA (6850); on Atom, it's the PPIA (8255).
// Both provide setTapeCarrier(), tone(), and receive/receiveBit().
poll(acia) {
Iif (this.curChunk === null) return;
// Atom: deliver one wavebit per poll.
if (this.isAtom && this.atomWavebitsLeft > 0) {
if (++this.atomSubCount >= this.atomToggleEvery) {
this.atomPhase ^= 1;
this.atomSubCount = 0;
}
acia.receiveBit(this.atomPhase);
this.atomWavebitsLeft--;
return secsToClocks(0.25 / this.baseFrequency, this.cpuSpeed);
}
if (this.state === -1) {
if (this.stream.eof()) {
this.curChunk = null;
return;
}
this.curChunk = this.readChunk();
}
let gap;
switch (this.curChunk.id) {
case 0x0000:
console.log("Origin: " + this.curChunk.stream.readNulString());
break;
case 0x0100:
acia.setTapeCarrier(false);
if (this.state === -1) {
this.state = 0;
this.curByte = this.curChunk.stream.readByte();
acia.tone(this.baseFrequency); // Start bit
} else if (this.state < 9) {
if (this.state === 0) {
// Start bit
acia.tone(this.baseFrequency);
if (this.isAtom) this.queueAtomBit(false);
} else {
const bit = this.curByte & (1 << (this.state - 1));
acia.tone(bit ? 2 * this.baseFrequency : this.baseFrequency);
if (this.isAtom) this.queueAtomBit(!!bit);
}
this.state++;
} else {
acia.receive(this.curByte);
acia.tone(2 * this.baseFrequency); // Stop bit
if (this.isAtom) this.queueAtomBit(true);
if (this.curChunk.stream.eof()) {
this.state = -1;
} else {
this.state = 0;
this.curByte = this.curChunk.stream.readByte();
}
}
if (this.isAtom) return 0; // wavebits queued, drained on next poll
return this.cycles(1);
case 0x0104: // Defined data
acia.setTapeCarrier(false);
if (this.state === -1) {
this.numDataBits = this.curChunk.stream.readByte();
this.parity = this.curChunk.stream.readByte();
this.numStopBits = this.curChunk.stream.readByte();
this.numParityBits = this.parity !== ParityN ? 1 : 0;
// Atom: negative stop bits (high bit set) means short wave
this.shortWave = 0;
if (this.isAtom && this.numStopBits & 0x80) {
this.numStopBits = Math.abs(this.numStopBits - 256);
this.shortWave = 1;
}
console.log(
`Defined data with ${this.numDataBits}${String.fromCharCode(this.parity)}${this.shortWave ? "-" : ""}${this.numStopBits}`,
);
this.state = 0;
}
if (this.state === 0) {
if (this.curChunk.stream.eof()) {
this.state = -1;
} else {
this.curByte = this.curChunk.stream.readByte() & ((1 << this.numDataBits) - 1);
acia.tone(this.baseFrequency); // Start bit
if (this.isAtom) this.queueAtomBit(false);
this.state++;
}
} else if (this.state < 1 + this.numDataBits) {
const bit = this.curByte & (1 << (this.state - 1));
acia.tone(bit ? 2 * this.baseFrequency : this.baseFrequency);
if (this.isAtom) this.queueAtomBit(!!bit);
this.state++;
} else if (this.state < 1 + this.numDataBits + this.numParityBits) {
let bit = parityOf(this.curByte);
if (this.parity === ParityN) bit = !bit;
acia.tone(bit ? 2 * this.baseFrequency : this.baseFrequency);
if (this.isAtom) this.queueAtomBit(!!bit);
this.state++;
} else if (this.state < 1 + this.numDataBits + this.numParityBits + this.numStopBits) {
acia.tone(2 * this.baseFrequency); // Stop bits
if (this.isAtom) this.queueAtomBit(true);
this.state++;
} else {
acia.receive(this.curByte);
this.state = 0;
return 0;
}
if (this.isAtom) return 0;
return this.cycles(1);
case 0x0111: // Carrier tone with dummy data
if (this.state === -1) {
this.state = 0;
this.carrierBefore = this.curChunk.stream.readInt16();
this.carrierAfter = this.curChunk.stream.readInt16();
console.log("Carrier with", this.carrierBefore, this.carrierAfter);
}
if (this.state === 0) {
acia.setTapeCarrier(true);
acia.tone(2 * this.baseFrequency);
if (this.isAtom) this.queueAtomBit(true);
this.carrierBefore--;
if (this.carrierBefore <= 0) this.state = 1;
} else if (this.state < 11) {
acia.setTapeCarrier(false);
acia.tone(this.dummyData[this.state - 1] ? this.baseFrequency : 2 * this.baseFrequency);
if (this.isAtom) this.queueAtomBit(!this.dummyData[this.state - 1]);
if (this.state === 10) {
acia.receive(0xaa);
}
this.state++;
} else {
acia.setTapeCarrier(true);
acia.tone(2 * this.baseFrequency);
if (this.isAtom) this.queueAtomBit(true);
this.carrierAfter--;
if (this.carrierAfter <= 0) this.state = -1;
}
if (this.isAtom) return 0;
return this.cycles(1);
case 0x0114:
console.log("Ignoring security cycles");
break;
case 0x0115:
console.log("Ignoring polarity change");
break;
case 0x0110: // Carrier tone.
Eif (this.state === -1) {
this.state = 0;
this.count = this.curChunk.stream.readInt16();
// Each Atom carrier cycle expands to 16 wavebits, so
// divide the count to avoid 16x too many cycles.
if (this.isAtom) this.count = Math.max(1, (this.count / 16) | 0);
}
acia.setTapeCarrier(true);
acia.tone(2 * this.baseFrequency);
if (this.isAtom) this.queueAtomBit(true);
this.count--;
Eif (this.count <= 0) this.state = -1;
if (this.isAtom) return 0;
return this.cycles(1);
case 0x0113:
this.baseFrequency = this.curChunk.stream.readFloat32();
console.log("Frequency change ", this.baseFrequency);
break;
case 0x0112:
acia.setTapeCarrier(false);
gap = 1 / (2 * this.curChunk.stream.readInt16() * this.baseFrequency);
console.log("Tape gap of " + gap + "s");
acia.tone(0);
return secsToClocks(gap, this.cpuSpeed);
case 0x0116:
acia.setTapeCarrier(false);
gap = this.curChunk.stream.readFloat32();
console.log("Tape gap of " + gap + "s");
acia.tone(0);
return secsToClocks(gap, this.cpuSpeed);
default:
console.log("Skipping unknown chunk " + hexword(this.curChunk.id));
break;
}
return this.cycles(1);
}
// Queue 16 wavebits for an Atom tape bit. atomPhase and atomSubCount
// carry across calls so bit boundaries don't break carrier detection.
queueAtomBit(isOne) {
this.atomWavebitsLeft = 16;
this.atomToggleEvery = isOne ? 1 : 2;
}
cycles(count) {
return secsToClocks(count / this.baseFrequency, this.cpuSpeed);
}
}
const dividerTable = [1, 16, 64, -1];
class TapefileTape {
constructor(stream, model) {
this.count = 0;
this.stream = stream;
this.cpuSpeed = model.cyclesPerSecond;
}
rate(acia) {
let bitsPerByte = 9;
Eif (!(acia.cr & 0x80)) {
bitsPerByte++; // Not totally correct if the AUG is to be believed.
}
const divider = dividerTable[acia.cr & 0x03];
// http://beebwiki.mdfs.net/index.php/Serial_ULA says the serial rate is ignored
// for cassette mode.
const cpp = this.cpuSpeed / (19200 / divider);
return Math.floor(bitsPerByte * cpp);
}
get name() {
return this.stream.name;
}
/** @returns {Number} how far through the image the head is, 0 to 1 */
get position() {
return this.stream.pos / this.stream.end;
}
rewind() {
this.stream.seek(10);
}
poll(acia) {
if (this.stream.eof()) return 100000;
let byte = this.stream.readByte();
if (byte === 0xff) {
byte = this.stream.readByte();
if (byte === 0) {
acia.setTapeCarrier(false);
return 0;
} else if (byte === 0x04) {
acia.setTapeCarrier(true);
// Simulate 5 seconds of carrier.
return secsToClocks(5, this.cpuSpeed);
} else Iif (byte !== 0xff) {
throw "Got a weird byte in the tape";
}
}
acia.receive(byte);
return this.rate(acia);
}
}
export async function loadTapeFromData(name, data, model) {
const raw = stringToUint8Array(data);
Iif (raw && raw.length > 4 && raw[0] === 0x1f && raw[1] === 0x8b) {
console.log("Ungzipping " + name);
data = await ungzip(raw);
}
const stream = new DataStream(name, data);
if (stream.readByte(0) === 0xff && stream.readByte(1) === 0x04) {
console.log("Detected a 'tapefile' tape");
return new TapefileTape(stream, model);
}
if (stream.readNulString(0) === "UEF File!") {
console.log("Detected a UEF tape");
return new UefTape(stream, model);
}
throw new Error(`${name} is not a UEF or tapefile tape image`);
}
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