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// https://github.com/scarybeasts/beebjit
import { crc32 } from "./archive.js";
import { IbmDiscFormat } from "./disc-format.js";
import { hexbyte } from "./hex.js";
export const PulsesPerWord = 32;
// The 1770 datasheet's recommended MFM gaps, in bytes.
const MfmGap1_4Es = 60;
const MfmSync00s = 12;
const MfmGap2_4Es = 22;
const MfmGap3_4Es = 24;
class TrackBuilder {
/**
* @param {Track} track
*/
constructor(track) {
this._track = track;
this._track.length = IbmDiscFormat.bytesPerTrack;
this._index = 0;
this._pulsesIndex = 0;
this._lastMfmBit = 0;
this._isMfm = false;
this._crc = 0;
}
get track() {
return this._track;
}
setTrackLength() {
Iif (this._index > this._track.pulses2Us.length)
throw new Error(`Track buffer overflow in ${this._track.description}`);
Eif (this._index !== 0) this._track.length = this._index;
return this;
}
resetCrc() {
this._crc = IbmDiscFormat.crcInit(false);
return this;
}
appendFmDataAndClocks(data, clocks) {
Iif (this._index >= this._track.pulses2Us.length)
throw new Error(`Track buffer overflow in ${this._track.description}`);
this._track.pulses2Us[this._index++] = IbmDiscFormat.fmTo2usPulses(clocks, data);
this._isMfm = false;
this._crc = IbmDiscFormat.crcAddByte(this._crc, data);
return this;
}
appendFmByte(data) {
this.appendFmDataAndClocks(data, 0xff);
return this;
}
appendRepeatFmByte(data, count) {
for (let i = 0; i < count; ++i) this.appendFmByte(data);
return this;
}
fillFmByte(data) {
Iif (this._index >= this._track.pulses2Us.length)
throw new Error(`Track buffer overflow in ${this._track.description}`);
// Fill to standard track size or buffer capacity, whichever is smaller
const fillCount = Math.min(IbmDiscFormat.bytesPerTrack, this._track.pulses2Us.length) - this._index;
this.appendRepeatFmByte(data, fillCount);
return this;
}
appendFmChunk(bytes) {
for (const byte of bytes) this.appendFmByte(byte);
return this;
}
appendCrc() {
const firstByte = (this._crc >>> 8) & 0xff;
const secondByte = this._crc & 0xff;
if (this._isMfm) {
this.appendMfmByte(firstByte);
this.appendMfmByte(secondByte);
} else {
this.appendFmByte(firstByte);
this.appendFmByte(secondByte);
}
return this;
}
appendMfmPulses(pulses) {
Iif (this._index >= this._track.pulses2Us.length)
throw new Error(`Track buffer overflow in ${this._track.description}`);
const existingPulses = this._track.pulses2Us[this._index];
const mask = 0xffff << this._pulsesIndex;
this._pulsesIndex = (this._pulsesIndex + 16) & 31;
this._track.pulses2Us[this._index] = (existingPulses & mask) | (pulses << this._pulsesIndex);
if (this._pulsesIndex === 0) this._index++;
this._isMfm = true;
return this;
}
appendMfmByte(data) {
const { lastBit, pulses } = IbmDiscFormat.mfmTo2usPulses(this._lastMfmBit, data);
this._lastMfmBit = lastBit;
this.appendMfmPulses(pulses);
this._crc = IbmDiscFormat.crcAddByte(this._crc, data);
return this;
}
appendRepeatMfmByte(data, count) {
for (let i = 0; i < count; ++i) this.appendMfmByte(data);
return this;
}
appendMfm3xA1Sync() {
for (let i = 0; i < 3; ++i) {
this.appendMfmPulses(IbmDiscFormat.mfmA1Sync);
this._crc = IbmDiscFormat.crcAddByte(this._crc, 0xa1);
}
return this;
}
appendMfmChunk(bytes) {
for (const byte of bytes) this.appendMfmByte(byte);
return this;
}
fillMfmByte(data) {
Iif (this._index >= this._track.pulses2Us.length)
throw new Error(`Track buffer overflow in ${this._track.description}`);
// Fill to standard track size or buffer capacity, whichever is smaller
const maxFill = Math.min(IbmDiscFormat.bytesPerTrack, this._track.pulses2Us.length);
while (this._index < maxFill) this.appendMfmByte(data);
return this;
}
/**
* An FM sector: its ID record, gap 2 and data record.
* @param {{idMark: number, dataMark: number, track: number, head: number, sector: number, lengthCode: number,
* data: Uint8Array}} sector
*/
appendFmSector({ idMark, dataMark, track, head, sector, lengthCode, data }) {
return this.resetCrc()
.appendFmDataAndClocks(idMark, IbmDiscFormat.markClockPattern)
.appendFmChunk([track, head, sector, lengthCode])
.appendCrc()
.appendRepeatFmByte(0xff, IbmDiscFormat.stdGap2FFs)
.appendRepeatFmByte(0x00, IbmDiscFormat.stdSync00s)
.resetCrc()
.appendFmDataAndClocks(dataMark, IbmDiscFormat.markClockPattern)
.appendFmChunk(data)
.appendCrc();
}
/**
* An MFM sector as the 1770 datasheet lays it out: the sync before its ID record, the ID record, gap 2 and the
* data record.
* @param {{idMark: number, dataMark: number, track: number, head: number, sector: number, lengthCode: number,
* data: Uint8Array}} sector
*/
appendMfmSector({ idMark, dataMark, track, head, sector, lengthCode, data }) {
return this.appendRepeatMfmByte(0x00, MfmSync00s)
.resetCrc()
.appendMfm3xA1Sync()
.appendMfmChunk([idMark, track, head, sector, lengthCode])
.appendCrc()
.appendRepeatMfmByte(0x4e, MfmGap2_4Es)
.appendRepeatMfmByte(0x00, MfmSync00s)
.resetCrc()
.appendMfm3xA1Sync()
.appendMfmByte(dataMark)
.appendMfmChunk(data)
.appendCrc();
}
}
class RawDiscReader {
/**
* @param {Track} track
* @param {Number} bitOffset
*/
constructor(track, bitOffset) {
this._track = track;
this._pos = bitOffset;
}
readPulses() {
let pulsesPos = this._pos >>> 5;
const bitPos = this._pos & 0x1f;
let sourcePulses = this._track.pulses2Us[pulsesPos];
let pulses = (sourcePulses << bitPos) & 0xfffffffff;
Iif (pulsesPos === this._track.length) {
pulsesPos = 0;
this._pos = bitPos;
} else {
pulsesPos++;
this._pos += 32;
}
if (bitPos > 0) {
sourcePulses = this._track.pulses2Us[pulsesPos];
pulses |= sourcePulses >>> (32 - bitPos);
}
return pulses;
}
}
class MfmReader {
/**
* @param {RawDiscReader} rawReader
*/
constructor(rawReader) {
this._rawReader = rawReader;
}
static pulsesPerByte = 16;
read(numBytes) {
const data = new Uint8Array(numBytes);
let pulses = 0;
for (let offset = 0; offset < numBytes; ++offset) {
if ((offset & 1) === 0) {
pulses = this._rawReader.readPulses();
} else {
pulses = (pulses << 16) & 0xffffffff;
}
data[offset] = IbmDiscFormat._2usPulsesToMfm(pulses >>> 16);
}
return { data, iffyPulses: false };
}
get initialCrc() {
let crc = IbmDiscFormat.crcInit(false);
crc = IbmDiscFormat.crcAddByte(crc, 0xa1);
crc = IbmDiscFormat.crcAddByte(crc, 0xa1);
crc = IbmDiscFormat.crcAddByte(crc, 0xa1);
return crc;
}
}
class FmReader {
/**
* @param {RawDiscReader} rawReader
*/
constructor(rawReader) {
this._rawReader = rawReader;
}
static pulsesPerByte = 32;
read(numBytes) {
const data = new Uint8Array(numBytes);
let iffyPulses = false;
for (let offset = 0; offset < numBytes; ++offset) {
const pulses = this._rawReader.readPulses();
const { data: dataByte, iffyPulses: iffy } = IbmDiscFormat._2usPulsesToFm(pulses);
data[offset] = dataByte;
iffyPulses |= iffy;
}
return { data, iffyPulses };
}
get initialCrc() {
return IbmDiscFormat.crcInit(false);
}
}
/**
* Where the sector decoder reports something odd on a track: what, and how far round the track, in
* pulses from the index.
* @typedef {function(string, number): void} DecoderWarning
*/
const ignoreWarnings = () => {};
class Sector {
/**
* @param {Track} track
* @param {boolean} isMfm
* @param {Number} idPosBitOffset
* @param {DecoderWarning} warn
*/
constructor(track, isMfm, idPosBitOffset, warn) {
this.track = track;
this.isMfm = isMfm;
this._readerType = isMfm ? MfmReader : FmReader;
this._warn = warn;
this.idPosBitOffset = idPosBitOffset;
this.dataPosBitOffset = null;
this.isDeleted = false;
this.sectorData = null;
this.hasDataCrcError = false;
this.byteLength = null;
const idReader = this._readerAt(this.idPosBitOffset);
const { data: headerData, iffyPulses } = idReader.read(6);
if (iffyPulses) {
this._warn(`iffy pulse in sector ${this.sectorNumber}'s header`, this.idPosBitOffset);
}
this.header = headerData;
let crc = idReader.initialCrc;
crc = IbmDiscFormat.crcAddByte(crc, IbmDiscFormat.idMarkDataPattern);
crc = IbmDiscFormat.crcAddBytes(crc, this.header.slice(0, 4));
const discCrc = (this.header[4] << 8) | this.header[5];
this.hasHeaderCrcError = crc !== discCrc;
}
_readerAt(bitOffset) {
return new this._readerType(new RawDiscReader(this.track, bitOffset));
}
get pulsesPerByte() {
return this._readerType.pulsesPerByte;
}
get trackNumber() {
return this.header ? this.header[0] : undefined;
}
get sectorNumber() {
return this.header ? this.header[2] : undefined;
}
get description() {
return `${this.track.description} idpos ${this.idPosBitOffset} idtrack ${this.trackNumber} idsector ${this.sectorNumber} datapos ${this.dataPosBitOffset}`;
}
/**
* @param {Sector|undefined} nextSector
*/
read(nextSector) {
if (this.dataPosBitOffset === null) {
this._warn(`sector ${this.sectorNumber}'s header has no data after it`, this.idPosBitOffset);
return;
}
const { pulsesPerByte } = this;
const dataMarker = this.isDeleted
? IbmDiscFormat.deletedDataMarkDataPattern
: IbmDiscFormat.dataMarkDataPattern;
const sectorStartByte = (this.dataPosBitOffset / pulsesPerByte) | 0;
const sectorEndByte =
(nextSector
? nextSector.idPosBitOffset / pulsesPerByte
: (this.track.length * PulsesPerWord) / pulsesPerByte) | 0;
// Account for CRC and sync bytes.
let sectorSize = Sector.toSectorSize(sectorEndByte - sectorStartByte - 5);
this.hasDataCrcError = true;
let seenIffyData;
do {
const { crcOk, sectorData, iffyPulses } = this._tryLoadSectorData(dataMarker, sectorSize);
seenIffyData = iffyPulses;
if (crcOk) {
this.byteLength = sectorSize;
this.hasDataCrcError = false;
this.sectorData = sectorData;
break;
}
sectorSize = sectorSize >>> 1;
} while (sectorSize >= 128);
if (seenIffyData) {
this._warn(`iffy pulse in sector ${this.sectorNumber}'s data`, this.dataPosBitOffset);
}
}
_tryLoadSectorData(dataMarker, sectorSize) {
const dataReader = this._readerAt(this.dataPosBitOffset);
let crc = IbmDiscFormat.crcAddByte(dataReader.initialCrc, dataMarker);
const { data: sectorData, iffyPulses } = dataReader.read(sectorSize + 2);
crc = IbmDiscFormat.crcAddBytes(crc, sectorData.slice(0, sectorSize));
const dataCrc = (sectorData[sectorSize] << 8) | sectorData[sectorSize + 1];
// The CRC bytes are used for error-checking and are not part of the actual sector data payload.
// Therefore, we exclude the last two bytes (CRC) from the returned `sectorData`.
return { crcOk: dataCrc === crc, sectorData: sectorData.slice(0, sectorSize), iffyPulses };
}
static toSectorSize(size) {
if (size < 256) return 128;
if (size < 512) return 256;
if (size < 1024) return 512;
if (size < 2048) return 1024;
return 2048;
}
}
/**
* A 64 bit shift register, held as a pair of unsigned 32 bit halves. BigInt would say this more
* directly but costs an order of magnitude more per bit shifted.
*/
export class BitWindow64 {
constructor() {
this.hi = 0;
this.lo = 0;
}
/**
* @param {Number} bit 0 or 1, shifted into bit 0
*/
shiftIn(bit) {
this.hi = ((this.hi << 1) | (this.lo >>> 31)) >>> 0;
this.lo = ((this.lo << 1) | bit) >>> 0;
}
/**
* @returns {boolean} whether all 64 bits match the halves given
*/
equals(hi, lo) {
return this.hi === hi && this.lo === lo;
}
/**
* @param {Number} nibble
* @returns {Number} the length of the run of `nibble` ending at bit 0
*/
countTrailingNibbles(nibble) {
const nibblesPerHalf = 8;
let count = 0;
for (let bits = this.lo; (bits & 0xf) === nibble; bits >>>= 4) count++;
// Only a low half that matched all the way up can have a run continuing into the high half.
if (count === nibblesPerHalf) for (let bits = this.hi; (bits & 0xf) === nibble; bits >>>= 4) count++;
return count;
}
/** @returns {string} the 64 bits as an unsigned decimal, the form snapshots store */
snapshotState() {
return ((BigInt(this.hi) << 32n) | BigInt(this.lo)).toString();
}
/** @param {string} decimal from snapshotState */
restoreState(decimal) {
const value = BigInt(decimal);
this.hi = Number(value >> 32n);
this.lo = Number(value & 0xffffffffn);
}
}
const BitWindowBits = 64;
// What the mark detector holds at an address mark. The FM case only pins down the high half,
// the tail of the zero sync run; the low half is the marker byte itself, decoded separately.
const FmSyncHi = 0x88888888;
const MfmMarkerHi = 0xaaaa4489;
const MfmMarkerLo = 0x44894489;
// FM puts each data bit's clock pulse in the top bit of its nibble.
const FmClockPulses = 0x88888888;
const FmMarkClockPulses = IbmDiscFormat.fmTo2usPulses(IbmDiscFormat.markClockPattern, 0);
// One data bit of zero, FM encoded with its clock, is the pulse nibble 0x8.
const FmZeroBitPulses = 0x8;
// FmSyncHi is eight of those, so a match has already seen this much of the sync run.
const FmSyncHiZeroBits = 8;
// Sync is counted in zero data bits, so a run no longer than two bytes' worth is short enough
// to be worth logging.
const ShortSyncZeros = 16;
class Track {
constructor(upper, trackNum, initialByte) {
this.length = IbmDiscFormat.bytesPerTrack; // Default size, will be updated when track is populated
this.upper = upper;
this.trackNum = trackNum;
// Make room for any extra pulses that might come from non-standard discs.
this.pulses2Us = new Uint32Array(IbmDiscFormat.bytesPerTrack * 2);
this.pulses2Us.fill(initialByte | (initialByte << 8) | (initialByte << 16) | (initialByte << 24));
}
get description() {
return `Track ${this.trackNum} ${this.upper ? "upper" : "lower"}`;
}
/**
* Debug functionality to try and interpret the track.
* @param {DecoderWarning} [warn] where to report anomalies; nowhere by default
* @returns {Sector[]}
*/
findSectors(warn = ignoreWarnings) {
const sectors = this.findSectorIds(warn);
for (let sectorIndex = 0; sectorIndex !== sectors.length; ++sectorIndex) {
const nextSector = sectors[sectorIndex + 1]; // Will be unset for last
sectors[sectorIndex].read(nextSector);
}
return sectors;
}
/**
* @param {Number} bitIndex
* @returns {Number} the pulse at `bitIndex`, 0 or 1; the first word's top bit is bit 0
*/
_pulseAt(bitIndex) {
const word = this.pulses2Us[Math.floor(bitIndex / PulsesPerWord)];
const bitFromTop = bitIndex % PulsesPerWord;
return (word >>> (PulsesPerWord - 1 - bitFromTop)) & 1;
}
/**
* @param {Number} lastBit
* @returns {BitWindow64} the pulses up to and including `lastBit`; bits before the track's start
* read as zero
*/
_pulseWindowEndingAt(lastBit) {
const window = new BitWindow64();
const firstBit = Math.max(0, lastBit - BitWindowBits + 1);
for (let bit = firstBit; bit <= lastBit; ++bit) window.shiftIn(this._pulseAt(bit));
return window;
}
/**
* @param {DecoderWarning} [warn] where to report anomalies; nowhere by default
* @returns {Sector[]}
*/
findSectorIds(warn = ignoreWarnings) {
const sectors = [];
// Pass 1: walk the track and find header and data markers.
const bitLength = this.length * 32;
let shiftRegister = 0;
let numShifts = 0;
let doMfmMarkerByte = false;
let isMfm = false;
let pulses = 0;
const markDetector = new BitWindow64();
let dataByte;
let sector = null;
for (let pulseIndex = 0; pulseIndex < bitLength; ++pulseIndex) {
if ((pulseIndex & 31) === 0) pulses = this.pulses2Us[pulseIndex >>> 5];
const pulseBit = pulses >>> 31;
markDetector.shiftIn(pulseBit);
shiftRegister = ((shiftRegister << 1) | pulseBit) & 0xffffffff;
numShifts++;
pulses = (pulses << 1) & 0xffffffff;
if (markDetector.hi === FmSyncHi && (markDetector.lo & FmClockPulses) >>> 0 === FmMarkClockPulses) {
const { clocks, data, iffyPulses } = IbmDiscFormat._2usPulsesToFm(markDetector.lo);
Iif (iffyPulses || clocks !== IbmDiscFormat.markClockPattern) continue;
isMfm = false;
doMfmMarkerByte = false;
const syncBefore = this._pulseWindowEndingAt(pulseIndex - BitWindowBits);
const num0s = FmSyncHiZeroBits + syncBefore.countTrailingNibbles(FmZeroBitPulses);
if (num0s <= ShortSyncZeros) {
warn("short zeros sync before an address mark", pulseIndex);
}
dataByte = data;
} else if (markDetector.equals(MfmMarkerHi, MfmMarkerLo)) {
// Next byte is MFM marker.
isMfm = true;
doMfmMarkerByte = true;
shiftRegister = 0;
numShifts = 0;
continue;
} else if (doMfmMarkerByte && numShifts === 16) {
dataByte = IbmDiscFormat._2usPulsesToMfm(shiftRegister);
doMfmMarkerByte = false;
} else {
continue;
}
switch (dataByte) {
case IbmDiscFormat.idMarkDataPattern: {
sector = new Sector(this, isMfm, pulseIndex + 1, warn);
sectors.push(sector);
shiftRegister = 0;
numShifts = 0;
break;
}
case IbmDiscFormat.dataMarkDataPattern:
case IbmDiscFormat.deletedDataMarkDataPattern:
Iif (!sector || sector.dataPosBitOffset) {
warn("sector data without a header", pulseIndex);
} else {
sector.dataPosBitOffset = pulseIndex + 1;
if (dataByte === IbmDiscFormat.deletedDataMarkDataPattern) {
sector.isDeleted = true;
}
shiftRegister = 0;
numShifts = 0;
}
break;
default:
warn(`unknown marker byte &${hexbyte(dataByte)}`, pulseIndex);
}
}
return sectors;
}
}
class Side {
constructor(upper, initialByte) {
this.tracks = [];
for (let i = 0; i < IbmDiscFormat.tracksPerDisc; ++i) this.tracks[i] = new Track(upper, i, initialByte);
}
}
/** How an image's tracks are laid out on the surface, and whether that is for the loader to decide. */
export const DiscLayout = Object.freeze({
auto: "auto",
contiguous: "contiguous",
expanded40: "expanded40",
});
export class DiscConfig {
constructor() {
this.expandTo80 = false;
this.isSkipOddTracks = false;
this.isSkipUpperSide = false;
}
}
// Acorn's *FORM puts each track's sector 0 three slots later than the track before, as do Greaseweazle and FlashFloppy
// for SSDs, which leaves room to step and settle before it comes round.
const SsdTrackSkew = 3;
// Both formats' sectors are 256 bytes, which an ID record's length code gives as 128 << 1.
const SectorLengthCode = 1;
const SsdSectorSize = 256;
const SsdSectorsPerTrack = 10;
const SsdTracksPerDisc = 80;
const SsdTrackSize = SsdSectorSize * SsdSectorsPerTrack;
/** @returns {Number} how many logical tracks of `data` hold anything, ignoring a run of trailing zeros */
function tracksWithData(data, numSides) {
let lastUsed = data.length - 1;
while (lastUsed >= 0 && data[lastUsed] === 0) lastUsed--;
return Math.floor(lastUsed / (SsdTrackSize * numSides)) + 1;
}
// The DFS catalogue is the first two sectors of a side. Sector 1 holds how many files there are and
// how many sectors the disc has.
const DfsEntryCountOffset = 0x105;
const DfsSectorCountOffset = 0x106;
const DfsEntrySize = 8;
const DfsMaxEntries = 31;
/**
* Whether an SSD or DSD image was written by a 40 track drive. Only its catalogue can say: images
* are routinely padded out or cut short, so their size means nothing.
*
* @param {Uint8Array} data
* @param {boolean} isDsd
* @returns {{is40Track: boolean, reason: string}}
*/
export function sniffDfsLayout(data, isDsd) {
const contiguous = (reason) => ({ is40Track: false, reason });
if (data.length < 2 * SsdSectorSize) return contiguous("it is smaller than a catalogue");
const entryBytes = data[DfsEntryCountOffset];
if (entryBytes % DfsEntrySize !== 0 || entryBytes > DfsMaxEntries * DfsEntrySize)
return contiguous(`its catalogue claims ${entryBytes} bytes of file entries`);
const sectors = ((data[DfsSectorCountOffset] & 3) << 8) | data[DfsSectorCountOffset + 1];
const reason = `its catalogue claims ${sectors} sectors`;
const fortyTrackSectors = (SsdTracksPerDisc / 2) * SsdSectorsPerTrack;
if (sectors === 0 || sectors > fortyTrackSectors) return contiguous(reason);
const tracks = tracksWithData(data, isDsd ? 2 : 1);
if (tracks > IbmDiscFormat.tracksPerDisc / 2) return contiguous(`it holds data as far as track ${tracks - 1}`);
return { is40Track: true, reason };
}
// The title is split across the two catalogue sectors, and the cycle number follows its second half.
const DfsTitleFirstHalf = 8;
const DfsTitleSecondHalf = 4;
const DfsCycleOffset = 4;
const DfsEntryCountInSector1 = DfsEntryCountOffset - SsdSectorSize;
const isPrintableAscii = (byte) => byte >= 0x20 && byte < 0x7f;
/**
* What the DFS catalogue on one side of a loaded disc says it is called, and how many times it
* has been written to, which between them are what was on the sticker.
*
* @param {Disc} disc
* @param {boolean} [isSideUpper]
* @returns {{title: string, cycle: string}|null} null when the side holds no DFS catalogue
*/
export function dfsCatalogue(disc, isSideUpper = false) {
const sectors = new Map();
for (const sector of disc.getTrack(isSideUpper, 0).findSectors()) {
const usable =
!sector.hasHeaderCrcError && !sector.hasDataCrcError && sector.sectorData?.length === SsdSectorSize;
if (usable && !sectors.has(sector.sectorNumber)) sectors.set(sector.sectorNumber, sector.sectorData);
}
const sector0 = sectors.get(0);
const sector1 = sectors.get(1);
if (!sector0 || !sector1) return null;
const entryBytes = sector1[DfsEntryCountInSector1];
if (entryBytes % DfsEntrySize !== 0 || entryBytes > DfsMaxEntries * DfsEntrySize) return null;
const titleBytes = [...sector0.subarray(0, DfsTitleFirstHalf), ...sector1.subarray(0, DfsTitleSecondHalf)];
const title = String.fromCharCode(...titleBytes.filter(isPrintableAscii)).trimEnd();
return { title, cycle: hexbyte(sector1[DfsCycleOffset]) };
}
// One track could match by luck; a disc's worth of them could not.
const MinDoubleSteppedTracks = 4;
/**
* Whether a surface holds a 40 track format, going by where its sectors say they are: a track
* written by a 48 tpi head sits at twice the number its own headers claim, with nothing readable
* on the tracks between. Only a flux image can be asked this, since for any other format the
* layout is the loader's own doing.
*
* @param {Disc} disc
* @param {boolean} isSideUpper - the side to ask; a dual format disc's sides can differ
* @returns {{is40Track: boolean, reason: string}}
*/
export function sniffSurfaceLayout(disc, isSideUpper) {
let doubleStepped = 0;
// Track 0 is where it claims to be at either pitch, so it says nothing.
for (let trackNum = 1; trackNum < disc.tracksUsed; ++trackNum) {
const sectors = disc.getTrack(isSideUpper, trackNum).findSectorIds();
if (!sectors.length) continue;
if (trackNum & 1) return { is40Track: false, reason: `track ${trackNum} holds sectors of its own` };
if (sectors.some((sector) => sector.trackNumber === trackNum / 2)) doubleStepped++;
}
if (!doubleStepped) return { is40Track: false, reason: "no track sits at twice the number its sectors claim" };
if (doubleStepped < MinDoubleSteppedTracks) {
const sit = doubleStepped === 1 ? "track sits" : "tracks sit";
return { is40Track: false, reason: `only ${doubleStepped} ${sit} at twice the number their sectors claim` };
}
return { is40Track: true, reason: `${doubleStepped} tracks sit at twice the number their sectors claim` };
}
/**
* Load a disc image in SSD (Single Sided Disc) or DSD (Double Sided Disc) format
* @param {Disc} disc - The disc object to load into
* @param {Uint8Array} data - The disc image data
* @param {boolean} isDsd - True if loading a double-sided disc
* @param {function(Uint8Array): void} onChange - Optional callback when disc content changes
*/
export function loadSsd(disc, data, isDsd, onChange) {
const blankSector = new Uint8Array(SsdSectorSize);
const numSides = isDsd ? 2 : 1;
if (data.length % SsdSectorSize !== 0) {
const paddedLength = Math.ceil(data.length / SsdSectorSize) * SsdSectorSize;
const padded = new Uint8Array(paddedLength);
padded.set(data);
data = padded;
}
const maxSize = SsdSectorSize * SsdSectorsPerTrack * SsdTracksPerDisc * numSides;
Iif (data.length > maxSize) {
throw new Error("SSD file is too large");
}
disc.is40Track = disc.config.expandTo80;
const trackStep = disc.is40Track ? 2 : 1;
// Tracks twice as far apart are half as many, and an image can run past the last of them as
// far as the surface has room for.
const numTracks = Math.min(
IbmDiscFormat.tracksPerDisc / trackStep,
Math.max(SsdTracksPerDisc / trackStep, tracksWithData(data, numSides)),
);
for (let track = 0; track < numTracks; ++track) {
const firstSector = (SsdSectorsPerTrack - ((SsdTrackSkew * track) % SsdSectorsPerTrack)) % SsdSectorsPerTrack;
for (let side = 0; side < numSides; ++side) {
const trackOffset = (track * numSides + side) * SsdTrackSize;
const trackBuilder = disc.buildTrack(side === 1, track * trackStep);
// Sync pattern at start of track, as the index pulse starts, aka GAP 5.
trackBuilder
.appendRepeatFmByte(0xff, IbmDiscFormat.stdGap1FFs)
.appendRepeatFmByte(0x00, IbmDiscFormat.stdSync00s);
for (let slot = 0; slot < SsdSectorsPerTrack; ++slot) {
const sector = (firstSector + slot) % SsdSectorsPerTrack;
const offset = trackOffset + sector * SsdSectorSize;
trackBuilder.appendFmSector({
idMark: IbmDiscFormat.idMarkDataPattern,
dataMark: IbmDiscFormat.dataMarkDataPattern,
track,
head: 0,
sector,
lengthCode: SectorLengthCode,
data: offset < data.length ? data.subarray(offset, offset + SsdSectorSize) : blankSector,
});
if (slot !== SsdSectorsPerTrack - 1) {
// Sync pattern between sectors, aka GAP 3.
trackBuilder
.appendRepeatFmByte(0xff, IbmDiscFormat.std10SectorGap3FFs)
.appendRepeatFmByte(0x00, IbmDiscFormat.stdSync00s);
}
}
trackBuilder.fillFmByte(0xff);
}
}
if (onChange) {
// TODO(#822) maybe construct the disc directly with this stuff?
// TODO(#822) maybe change this entirely and make it lazy; and have the onChange "pull" the disc as the format it wants
// instead of doing this here. Most stuff doesn't care about changes and only needs the image on save.
// Create a dataCopy large enough for all the sectors and tracks.
const dataCopy = new Uint8Array(maxSize);
dataCopy.set(data);
disc.addTrackWriteListener(
/** @param {Track} trackObj */
(side, _trackNum, trackObj) => {
for (const sector of trackObj.findSectors())
if (!sectorShortfall(sector)) dataCopy.set(sector.sectorData, ssdOffsetOf(sector, side, numSides));
onChange(dataCopy);
},
true,
);
}
return disc;
}
const AdfSectorSize = 256;
const AdfSectorsPerTrack = 16;
const AdfTracksPerDisc = 80;
/**
* @param {Disc} disc
* @param {Uint8Array} data
* @param {boolean} isDsd
*/
export function loadAdf(disc, data, isDsd) {
const blankSector = new Uint8Array(AdfSectorSize);
const numSides = isDsd ? 2 : 1;
Iif (data.length % AdfSectorSize !== 0) {
throw new Error("ADF file size is not a multiple of sector size");
}
const maxSize = AdfSectorSize * AdfSectorsPerTrack * AdfTracksPerDisc * numSides;
Iif (data.length > maxSize) {
throw new Error("ADF file is too large");
}
let offset = 0;
for (let track = 0; track < AdfTracksPerDisc; ++track) {
if (offset >= data.length) break;
for (let side = 0; side < numSides; ++side) {
// Using recommended values from the 177x datasheet.
const trackBuilder = disc.buildTrack(side === 1, track);
trackBuilder.appendRepeatMfmByte(0x4e, MfmGap1_4Es);
for (let sector = 0; sector < AdfSectorsPerTrack; ++sector) {
trackBuilder.appendMfmSector({
idMark: IbmDiscFormat.idMarkDataPattern,
dataMark: IbmDiscFormat.dataMarkDataPattern,
track,
head: 0,
sector,
lengthCode: SectorLengthCode,
data: offset < data.length ? data.subarray(offset, offset + AdfSectorSize) : blankSector,
});
offset += AdfSectorSize;
// Sync pattern between sectors, aka GAP 3.
trackBuilder.appendRepeatMfmByte(0x4e, MfmGap3_4Es);
}
trackBuilder.fillMfmByte(0x4e);
}
}
// TODO(#822) writeback
return disc;
}
/** Why a sector will not fit in an SSD or DSD image, or null if it will. */
function sectorShortfall(sector) {
if (sector.hasDataCrcError || sector.hasHeaderCrcError) return "with a CRC error";
// A header whose data mark never arrives leaves the sector with nothing to write.
if (!sector.sectorData) return "with no data";
if (sector.sectorNumber >= SsdSectorsPerTrack) return `numbered past the ${SsdSectorsPerTrack} a track holds`;
Iif (sector.sectorData.length !== SsdSectorSize) return `not ${SsdSectorSize} bytes`;
Iif (sector.trackNumber >= SsdTracksPerDisc) return `past track ${SsdTracksPerDisc}`;
return null;
}
/**
* Where a sector belongs in an SSD or DSD image, which is the track its own header claims rather
* than the one it sits on.
*
* @param {Sector} sector
* @param {boolean} isSideUpper
* @param {Number} numSides
*/
function ssdOffsetOf(sector, isSideUpper, numSides) {
const track = sector.trackNumber * numSides + (isSideUpper ? 1 : 0);
return track * SsdTrackSize + sector.sectorNumber * SsdSectorSize;
}
/**
* @param {Disc} disc
* @returns {{sector: Sector, isSideUpper: boolean}[]} every sector on `disc`, track by track
*/
function sectorsOnSurface(disc) {
const found = [];
for (let trackNum = 0; trackNum < disc.tracksUsed; ++trackNum) {
for (const isSideUpper of disc.isDoubleSided ? [false, true] : [false]) {
for (const sector of disc.getTrack(isSideUpper, trackNum).findSectors())
found.push({ sector, isSideUpper });
}
}
return found;
}
/**
* SSD and DSD images hold sector contents and nothing else, so anything a DFS sector could not
* have held is lost. Copy protection usually shows up as one of these.
*
* @param {{sector: Sector}[]} sectors
* @returns {string[]} what `sectors` hold that an SSD or DSD cannot, worst first
*/
function describeShortfalls(sectors) {
const counts = new Map();
for (const { sector } of sectors) {
const shortfall = sectorShortfall(sector);
if (shortfall) counts.set(shortfall, (counts.get(shortfall) ?? 0) + 1);
}
return [...counts]
.sort(([, a], [, b]) => b - a)
.map(([shortfall, count]) => `${count} sector${count === 1 ? "" : "s"} ${shortfall}`);
}
/**
* @returns {Uint8Array}
* @param {Disc} disc
* @param {object} [options]
* @param {boolean} [options.force] save what fits instead of refusing a disc that will not fit
* @throws if the disc holds anything an SSD or DSD cannot, and `force` is not set
*/
export function toSsdOrDsd(disc, { force = false } = {}) {
const sectors = sectorsOnSurface(disc);
if (!force) {
const shortfalls = describeShortfalls(sectors);
if (shortfalls.length)
throw new Error(
`This disc cannot be saved as SSD or DSD: it has ${shortfalls.join(", ")}. ` +
`Save it as HFE to keep everything.`,
);
}
const numSides = disc.isDoubleSided ? 2 : 1;
const result = new Uint8Array(numSides * SsdTracksPerDisc * SsdTrackSize);
let numTracks = 0;
for (const { sector, isSideUpper } of sectors) {
if (sectorShortfall(sector)) continue;
result.set(sector.sectorData, ssdOffsetOf(sector, isSideUpper, numSides));
numTracks = Math.max(numTracks, sector.trackNumber + 1);
}
return result.slice(0, numTracks * numSides * SsdTrackSize);
}
export class Disc {
/**
* @returns {Disc} a new blank disc
*/
static createBlank() {
return new Disc(true, new DiscConfig());
}
/**
* @param {boolean} isWriteable
* @param {DiscConfig} config
* @param {string} name
*/
constructor(isWriteable, config, name) {
this.config = config;
this.name = name;
this.isDirty = false;
this.dirtySide = -1;
this.dirtyTrack = -1;
this.tracksUsed = 0;
this.isDoubleSided = false;
// Whether the surface holds a 48 tpi layout, which a drive reads by double stepping.
this.is40Track = false;
/** @type {{text: string, isOdd: boolean}[]} what loading the image found out, for the media window */
this.loadNotes = [];
this._trackWriteListeners = new Set();
this._savingListeners = new Set();
this.isWriteable = isWriteable;
// Track which tracks have been written since the last snapshot.
// Keys are numeric: (track | (isSideUpper ? 0x100 : 0)).
this._snapshotDirtyTracks = new Set();
// Cumulative set of all tracks ever written since disc load (never cleared by snapshots).
// Same key encoding as _snapshotDirtyTracks.
this._everDirtyTracks = new Set();
// Cache of the previous snapshot's track data for structural sharing.
// Keys are "side:trackNum" strings, values are {pulses2Us, length} objects.
this._lastTrackSnapshots = Object.create(null);
// Original disc image data, stored for embedding in save-to-file snapshots
// and CRC32 verification on restore. _originalImageData is only set for
// local-file discs (not URL-sourced ones). _originalImageCrc32 is the CRC
// of the image bytes at load time — it is not updated if an onChange handler
// mutates the backing store. This is fine because the CRC is compared against
// the same source that would be reloaded (the original image or URL), not the
// mutated copy. If a mutable source URL were added in future, CRC verification
// should be skipped or the CRC updated accordingly.
this._originalImageData = null;
this._originalImageCrc32 = null;
this.initSurface(0);
}
/**
* @param {function(boolean, Number, Track): void} listener called once per flushed track
* @param {boolean} [savesChanges] whether the listener puts the image somewhere it is read back from
*/
addTrackWriteListener(listener, savesChanges = false) {
this._trackWriteListeners.add(listener);
if (savesChanges) this._savingListeners.add(listener);
}
get savesChanges() {
return this._savingListeners.size > 0;
}
/** @param {function(boolean, Number, Track): void} listener */
removeTrackWriteListener(listener) {
this._trackWriteListeners.delete(listener);
this._savingListeners.delete(listener);
}
/** @param {function(): void} listener called once, when a track is first written to this disc */
notifyOnFirstTrackWrite(listener) {
const onFirstWrite = () => {
this.removeTrackWriteListener(onFirstWrite);
listener();
};
this.addTrackWriteListener(onFirstWrite);
}
/**
* Record the CRC32 of the original disc image for verification on restore.
* Called by discFor() after loading. Does not retain the image bytes.
* @param {Uint8Array} data - the raw disc image bytes (used only to compute CRC32)
*/
setOriginalImageCrc32(data) {
this._originalImageCrc32 = crc32(data);
}
/**
* Store the original disc image bytes for embedding in snapshots.
* Only call this for local-file discs — URL-sourced discs should use
* setOriginalImageCrc32() instead to avoid retaining the full image.
* Computes CRC32 only if not already set (e.g. by discFor).
* @param {Uint8Array} data - the raw disc image bytes
*/
setOriginalImage(data) {
this._originalImageData = data;
if (this._originalImageCrc32 == null) {
this._originalImageCrc32 = crc32(data);
}
}
/** @returns {Uint8Array|null} the original disc image bytes, or null if not set */
get originalImageData() {
return this._originalImageData;
}
/** @returns {number|null} CRC32 of the original disc image, or null if not set */
get originalImageCrc32() {
return this._originalImageCrc32;
}
get writeProtected() {
return !this.isWriteable;
}
/**
* @param {boolean} isSideUpper
* @param {Number} trackNum
* @returns {Track} */
getTrack(isSideUpper, trackNum) {
return isSideUpper ? this.upperSide.tracks[trackNum] : this.lowerSide.tracks[trackNum];
}
buildTrack(isSideUpper, trackNum) {
this.setTrackUsed(isSideUpper, trackNum);
return new TrackBuilder(this.getTrack(isSideUpper, trackNum));
}
setTrackUsed(isSideUpper, trackNum) {
if (isSideUpper) this.isDoubleSided = true;
this.tracksUsed = Math.max(this.tracksUsed, trackNum + 1);
}
initSurface(initialByte) {
this.lowerSide = new Side(false, initialByte);
this.upperSide = new Side(true, initialByte);
this.tracksUsed = 0;
this.isDoubleSided = false;
}
readPulses(isSideUpper, track, position) {
return this.getTrack(isSideUpper, track).pulses2Us[position];
}
/**
* @param {boolean} isSideUpper
* @param {Number} track
* @param {Number} position
* @param {Number} pulses
*/
writePulses(isSideUpper, track, position, pulses) {
const trackObj = this.getTrack(isSideUpper, track);
Iif (position >= trackObj.length)
throw new Error(
`Attempt to write off end of track ${track}: position ${position} >= length ${trackObj.length}`,
);
Iif (this.isDirty) {
if (isSideUpper !== this.dirtySide || track !== this.dirtyTrack)
throw new Error("Switched dirty track or side");
}
this.isDirty = true;
this.dirtySide = isSideUpper;
this.dirtyTrack = track;
// Numeric key avoids string allocation on every pulse write.
// Upper bit encodes side, lower 8 bits encode track number.
const dirtyKey = track | (isSideUpper ? 0x100 : 0);
this._snapshotDirtyTracks.add(dirtyKey);
this._everDirtyTracks.add(dirtyKey);
trackObj.pulses2Us[position] = pulses;
}
/** @returns {?{isSideUpper: boolean, trackNum: Number}} the track written, if there was one */
flushWrites() {
if (!this.isDirty) {
Iif (this.dirtySide !== -1 || this.dirtyTrack !== -1) throw new Error("Bad state in disc dirty tracking");
return null;
}
const dirtySide = this.dirtySide;
const dirtyTrack = this.dirtyTrack;
this.isDirty = false;
this.dirtySide = -1;
this.dirtyTrack = -1;
const trackObj = this.getTrack(dirtySide, dirtyTrack);
this.setTrackUsed(dirtySide, dirtyTrack);
for (const listener of this._trackWriteListeners) listener(dirtySide, dirtyTrack, trackObj);
return { isSideUpper: dirtySide, trackNum: dirtyTrack };
}
/**
* Leave a track with no flux on it at all, as an erase head does.
*
* @param {boolean} isSideUpper
* @param {Number} trackNum
*/
eraseTrack(isSideUpper, trackNum) {
const trackObj = this.getTrack(isSideUpper, trackNum);
trackObj.pulses2Us.fill(0);
trackObj.length = IbmDiscFormat.bytesPerTrack;
const dirtyKey = trackNum | (isSideUpper ? 0x100 : 0);
this._snapshotDirtyTracks.add(dirtyKey);
this._everDirtyTracks.add(dirtyKey);
this.setTrackUsed(isSideUpper, trackNum);
for (const listener of this._trackWriteListeners) listener(isSideUpper, trackNum, trackObj);
}
/**
* Create a snapshot of all track data with structural sharing.
* Clean tracks reuse references from the previous snapshot;
* dirty tracks get fresh copies.
*/
snapshotState() {
const numSides = this.isDoubleSided ? 2 : 1;
// Use a plain object for JSON serialization compatibility.
// Keys are "side:trackNum" strings.
const tracks = Object.create(null);
for (let side = 0; side < numSides; ++side) {
for (let trackNum = 0; trackNum < this.tracksUsed; ++trackNum) {
const key = `${side === 1}:${trackNum}`;
const dirtyKey = trackNum | (side === 1 ? 0x100 : 0);
const trackObj = this.getTrack(side === 1, trackNum);
if (this._snapshotDirtyTracks.has(dirtyKey) || !this._lastTrackSnapshots[key]) {
// Dirty or first snapshot: copy the track data
tracks[key] = {
pulses2Us: trackObj.pulses2Us.slice(),
length: trackObj.length,
};
} else {
// Clean: reuse the previous snapshot's reference
tracks[key] = this._lastTrackSnapshots[key];
}
}
}
this._snapshotDirtyTracks.clear();
this._lastTrackSnapshots = tracks;
return {
tracksUsed: this.tracksUsed,
isDoubleSided: this.isDoubleSided,
isWriteable: this.isWriteable,
name: this.name,
tracks,
// Expose for save-to-file snapshots to identify dirty tracks.
// This is a Set and won't survive JSON serialization — it's only
// used by createSnapshot() before the snapshot is serialized.
_everDirtyTracks: new Set(this._everDirtyTracks),
_originalImageData: this._originalImageData,
_originalImageCrc32: this._originalImageCrc32,
};
}
/**
* Restore disc track data from a snapshot.
* For save-to-file snapshots, `state.tracks` is empty and `state.dirtyTracks`
* contains only the tracks modified since disc load. The base disc data must
* already be loaded before calling this method.
*/
restoreState(state) {
this.tracksUsed = state.tracksUsed;
this.isDoubleSided = state.isDoubleSided;
this.isWriteable = state.isWriteable;
this.name = state.name;
// Reset write-in-progress state
this.isDirty = false;
this.dirtySide = -1;
this.dirtyTrack = -1;
this._snapshotDirtyTracks.clear();
// Restore _everDirtyTracks from the snapshot if present (rewind path —
// the Set is carried in-memory but won't survive JSON serialization).
// For the save-to-file path, _everDirtyTracks is rebuilt from dirtyTracks below.
if (state._everDirtyTracks instanceof Set) {
this._everDirtyTracks = new Set(state._everDirtyTracks);
} else {
this._everDirtyTracks.clear();
}
// Restore full track data (rewind path — tracks contains all data)
this._lastTrackSnapshots = state.tracks;
for (const key of Object.keys(state.tracks)) {
const trackData = state.tracks[key];
const [sideStr, trackNumStr] = key.split(":");
const isSideUpper = sideStr === "true";
const trackNum = parseInt(trackNumStr, 10);
const trackObj = this.getTrack(isSideUpper, trackNum);
trackObj.pulses2Us.set(trackData.pulses2Us);
trackObj.length = trackData.length;
}
// Apply dirty track overlays (save-to-file path — base disc already loaded,
// overlay only the tracks that were written since disc load)
if (state.dirtyTracks) {
for (const key of Object.keys(state.dirtyTracks)) {
const trackData = state.dirtyTracks[key];
const [sideStr, trackNumStr] = key.split(":");
const isSideUpper = sideStr === "true";
const trackNum = parseInt(trackNumStr, 10);
const trackObj = this.getTrack(isSideUpper, trackNum);
trackObj.pulses2Us.set(trackData.pulses2Us);
trackObj.length = trackData.length;
this._everDirtyTracks.add(trackNum | (isSideUpper ? 0x100 : 0));
// A disc that keeps its changes at its source takes the overlay there too.
for (const listener of this._trackWriteListeners) listener(isSideUpper, trackNum, trackObj);
}
}
}
}
/** @returns {string} the numbers in order, each once, with runs of consecutive ones folded, as "3-5, 9" */
export function numberRuns(numbers) {
const runs = [];
for (const number of new Set(numbers.toSorted((a, b) => a - b))) {
const last = runs.at(-1);
if (last && last.to === number - 1) last.to = number;
else runs.push({ from: number, to: number });
}
return runs.map(({ from, to }) => (from === to ? `${from}` : `${from}-${to}`)).join(", ");
}
// A track within this of the standard length is not worth remarking on.
const TrackLengthTolerance = 0.015;
const StandardFmSectors = [10];
const StandardMfmSectors = [16, 18];
/**
* What is odd about one side of a disc, track by track: long or short tracks, unusual sector
* counts, CRC errors, sectors that claim another track, anything the decoder warns of, and runs of
* tracks with no sectors. A double stepped side's tracks are numbered as its sectors number them.
*
* @param {Disc} disc
* @param {boolean} isSideUpper
* @returns {{trackNum: number, fraction: number, text: string}[]} each finding, with the physical
* track it is on and how far round that track
*/
export function discReport(disc, isSideUpper) {
const findings = [];
const step = sniffSurfaceLayout(disc, isSideUpper).is40Track ? 2 : 1;
// Tracks with no sectors and nothing else to say come in runs, each told in one line.
let run = null;
const endRun = () => {
if (!run) return;
const { from, to, what } = run;
const tracks = from === to ? `track ${from / step}` : `tracks ${from / step}-${to / step}`;
findings.push({ trackNum: from, fraction: 0, text: `${tracks}: ${what}` });
run = null;
};
for (let trackNum = 0; trackNum < disc.tracksUsed; trackNum += step) {
const track = disc.getTrack(isSideUpper, trackNum);
const claimed = trackNum / step;
const pulsesRound = track.length * PulsesPerWord;
const onTrack = [];
const note = (text, pulse) =>
onTrack.push({ trackNum, fraction: pulse / pulsesRound, text: `track ${claimed}: ${text}` });
const sectors = track.findSectors(note);
if (!sectors.length && !onTrack.length) {
// Unformatted as the surface shows it: no flux at all.
const isBlank = track.pulses2Us.subarray(0, track.length).every((pulses) => pulses === 0);
const what = isBlank ? "unformatted" : "flux, but no sector IDs";
if (run?.what !== what) endRun();
run = { from: run?.from ?? trackNum, to: trackNum, what };
continue;
}
endRun();
Iif (!sectors.length) {
note("flux, but no sector IDs", 0);
findings.push(...onTrack);
continue;
}
const lengthRatio = track.length / IbmDiscFormat.bytesPerTrack;
if (Math.abs(lengthRatio - 1) >= TrackLengthTolerance)
note(`${lengthRatio > 1 ? "long" : "short"}, ${Math.round(lengthRatio * 100)}% of the standard length`, 0);
const isMfm = sectors[0].isMfm;
if (!(isMfm ? StandardMfmSectors : StandardFmSectors).includes(sectors.length))
note(`${sectors.length} ${isMfm ? "MFM" : "FM"} ${sectors.length === 1 ? "sector" : "sectors"}`, 0);
// Sectors that share a fault are named together, at the first of them.
const faults = new Map();
const fault = (what, sector) => {
const found = faults.get(what) ?? { at: sector.idPosBitOffset, sectorNums: [] };
found.sectorNums.push(sector.sectorNumber);
faults.set(what, found);
};
for (const sector of sectors) {
if (sector.hasHeaderCrcError) fault("a bad header CRC", sector);
if (sector.trackNumber !== claimed) fault(`a header claiming track ${sector.trackNumber}`, sector);
if (sector.hasDataCrcError) fault("a bad data CRC", sector);
}
for (const [what, { at, sectorNums }] of faults)
note(`${sectorNums.length === 1 ? "sector" : "sectors"} ${numberRuns(sectorNums)} with ${what}`, at);
findings.push(...onTrack);
}
endRun();
return findings;
}
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