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* MachineSession - wraps jsbeeb's TestMachine with:
* - real Video framebuffer (so screenshots work)
* - accumulated text output between calls
* - clean lifecycle (boot, interact, screenshot, destroy)
*/
import { readFileSync } from "fs";
import { fileURLToPath } from "url";
import path from "path";
import { TestMachine } from "./test-machine.js";
import { VduTextCapture } from "./vdu-capture.js";
import { InstrumentedSoundChip, FakeSoundChip } from "./soundchip.js";
// Resolve the jsbeeb package root from our own location (src/machine-session.js
// → go up one level). Passed to setNodeBasePath() so the ROM loader resolves
// files relative to this package regardless of the calling process's cwd.
const _jsbeebRoot = path.dirname(path.dirname(fileURLToPath(import.meta.url)));
import * as fdc from "./fdc.js";
import { MediaResolver } from "./media-resolver.js";
import { StairwayToHell } from "./sth.js";
import { BitshiftersArchive } from "./bitshifters.js";
import { BbcDiscArchive } from "./bbcdiscs.js";
import { Video } from "./video.js";
import { findModel } from "./models.js";
import { setNodeBasePath } from "./loader.js";
// BBC framebuffer is 1024×625 pixels
const FB_WIDTH = 1024;
const FB_HEIGHT = 625;
// Bit X of ACCCON: shadow RAM in place of main at &3000 to &7FFF.
const AccconShadowBit = 4;
// Five times a frame, so only a machine that has stopped painting hits it.
const BackstopSecondsPerFrame = 0.1;
export class MachineSession {
/**
* @param {string} modelName - e.g. "B-DFS1.2", "Master"
* @param {Object} [opts]
* @param {string} [opts.discImage] - path to an .ssd or .dsd disc image to load on boot
* @param {boolean} [opts.tube] - attach a 65C02 second processor (Tube co-processor)
* @param {number} [opts.cpuMultiplier] - run the CPU this many times faster than the peripherals
* @param {boolean} [opts.hasTeletextAdaptor] - fit the Acorn teletext adaptor
*/
constructor(modelName = "B-DFS1.2", opts = {}) {
this.modelName = modelName;
this._opts = opts;
// Raw RGBA framebuffer. The Video chip renders into _fb32 (cleared each frame).
// _completeFb8 is a snapshot taken at paint time (the equivalent of the browser canvas)
// and is what screenshot() reads from, always a complete frame, never mid-render.
this._fb8 = new Uint8Array(FB_WIDTH * FB_HEIGHT * 4);
this._fb32 = new Uint32Array(this._fb8.buffer);
this._completeFb8 = new Uint8Array(FB_WIDTH * FB_HEIGHT * 4);
this._lastPaint = { minx: 0, miny: 0, maxx: FB_WIDTH, maxy: FB_HEIGHT };
this._frameDirty = false;
this._frameCount = 0;
this._stopAtFrame = Infinity;
// Create a real Video instance so we get pixel output
const modelObj = findModel(modelName);
this._isAtom = modelObj.isAtom;
this._video = new Video(
modelObj.isMaster,
this._fb32,
(minx, miny, maxx, maxy) => {
this._lastPaint = { minx, miny, maxx, maxy };
this._frameDirty = true;
// Snapshot the complete frame now, before clearPaintBuffer() wipes _fb32.
// This mirrors what the browser does: paint_ext fires → canvas updated → fb32 cleared.
this._completeFb8.set(this._fb8);
this._frameCount++;
if (this._frameCount >= this._stopAtFrame) this._machine.processor.stop();
},
{ isAtom: modelObj.isAtom },
);
// Use a real (instrumented) sound chip so we can read registers and capture writes.
// Atom models use AtomSoundChip which has a different interface (speakerGenerator,
// toneGenerator); FakeSoundChip provides compatible no-op stubs for headless mode.
this._soundChip = modelObj.isAtom ? new FakeSoundChip() : new InstrumentedSoundChip();
// TestMachine forwards these to fake6502
this._machine = new TestMachine(modelName, {
video: this._video,
soundChip: this._soundChip,
tube: opts.tube,
cpuMultiplier: opts.cpuMultiplier,
hasTeletextAdaptor: opts.hasTeletextAdaptor,
});
// Accumulated VDU text output, drained by callers
this._pendingOutput = [];
this._capture = new VduTextCapture((element) => this._pendingOutput.push(element), { isAtom: this._isAtom });
// Breakpoint management, with persistent hooks that survive across run calls
this._breakpoints = new Map(); // id → { hook, type, address, hit }
this._nextBreakpointId = 1;
}
/** Load ROMs and hardware; call once before anything else */
async initialise() {
setNodeBasePath(_jsbeebRoot);
await this._machine.initialise();
if (this._opts.discImage) {
this.loadDisc(this._opts.discImage);
}
this._machine.onVduChar((c) => this._capture.onChar(c));
}
/**
* Boot the machine (run until the BASIC prompt).
* Returns captured boot-screen text (the OS banner etc.).
*/
async boot(timeoutSecs = 30) {
await this._machine.runUntilInput(timeoutSecs);
return this.drainOutput();
}
get _keyboard() {
return this._machine.processor.keyboardInterface;
}
/**
* The keyboard is the typist's until everything from type() has been
* delivered, and a key pressed meanwhile would be silently dropped.
*/
_requireKeyboard() {
if (this.typingPending) {
throw new Error(
"Text from type() is still being typed: await type(), or if a breakpoint stopped it " +
"run the machine on to finish it, or cancelTyping() first",
);
}
}
/**
* Press a host key by its physical position, as `KeyboardEvent.code` names it:
* "KeyA", "Digit1", "ShiftLeft", "NumpadEnter". The `keyCodes` table in keymap.js
* gives jsbeeb's own name for each, and a code not in it throws.
*/
keyDown(code, shiftDown = false) {
this._requireKeyboard();
this._machine.keyDown(code, shiftDown);
}
/** Release a host key, by the same `KeyboardEvent.code` name. */
keyUp(code) {
this._requireKeyboard();
this._machine.keyUp(code);
}
/**
* Press a key by its place in the keyboard matrix, as the model's key
* table (BBC or ATOM in the keymaps) gives it, with no host key map in
* between: a game reading the matrix sees exactly this key.
* @param {[number, number]} colRow
*/
keyDownRaw(colRow) {
this._requireKeyboard();
this._keyboard.keyDownRaw(colRow);
}
/**
* Release a key pressed by matrix position.
* @param {[number, number]} colRow
*/
keyUpRaw(colRow) {
this._requireKeyboard();
this._keyboard.keyUpRaw(colRow);
}
/**
* Every key currently down, as matrix positions keyDownRaw takes.
* @returns {Array<[number, number]>}
*/
heldKeys() {
const held = [];
this._keyboard.keys.forEach((column, col) => {
column.forEach((down, row) => {
if (down) held.push([col, row]);
});
});
return held;
}
/** Whether text from type() is still to be delivered, which a breakpoint stopping the run leaves behind. */
get typingPending() {
return this._machine.typist.isTyping;
}
/** Drop any text from type() still to be delivered, and give the keyboard back. */
cancelTyping() {
this._machine.typist.cancel();
}
/** Release every key, and drop any typing still pending, so the keyboard is in a known state. */
releaseAllKeys() {
this.cancelTyping();
this._keyboard.clearKeys();
}
/**
* Reset the machine.
* @param {boolean} [hard=true] - true for power-on reset, false for soft reset
*/
reset(hard = true) {
this._machine.processor.reset(hard);
this._pendingOutput = [];
}
/**
* Capture machine state and captured text as an opaque object for restore().
* Leaves the running session undisturbed.
*
* @param {Object} [opts]
* @param {boolean} [opts.includeRoms=true] - carry the ROM contents too.
* Only safe to omit when restoring into a session built from the same
* model, which is then left with whatever ROMs it already had.
*/
snapshot({ includeRoms = true } = {}) {
return {
machine: this._machine.snapshot({ includeRoms }),
pendingOutput: this._pendingOutput.map((element) => ({ ...element })),
capture: this._capture.snapshot(),
};
}
/**
* Put back a state from snapshot(). `elapsedCycles` rewinds with the
* machine; breakpoints belong to the session, not the machine, so they and
* their hit flags are left alone, and `frameCount` keeps counting the way it
* does across a hard reset.
*/
restore(state) {
this._machine.restore(state.machine);
this._pendingOutput = state.pendingOutput.map((element) => ({ ...element }));
this._capture.restore(state.capture);
}
/** Tokenise BBC BASIC source and write it into PAGE */
async loadBasic(source) {
await this._machine.loadBasic(source);
}
/**
* Simulate keypresses. Note: each character needs a short run to be
* picked up by the OS, so this is internally async and slow-ish (by
* emulated-time).
*/
async type(text) {
await this._machine.type(text);
}
/**
* Run the emulator until the OS is waiting at the keyboard prompt, or
* until timeoutSecs of emulated time elapses. Returns captured output.
*
* @param {number} [timeoutSecs=60]
* @param {Object} [opts]
* @param {boolean} [opts.clear=true] - Whether to clear the output buffer after returning it.
*/
async runUntilPrompt(timeoutSecs = 60, { clear = true } = {}) {
await this._machine.runUntilInput(timeoutSecs);
return this.drainOutput({ clear });
}
/**
* Run for an exact number of emulated CPU cycles, or until something stops
* the CPU first: a breakpoint, or the paint runFrames stops at. `completed`
* is false if it was stopped short.
* @returns {Promise<{cyclesRun: number, completed: boolean}>}
*/
async runFor(cycles) {
const startCycles = this.elapsedCycles;
const stopped = await this._machine.runFor(cycles);
return { cyclesRun: this.elapsedCycles - startCycles, completed: !stopped };
}
/** Emulated cycles since power-on */
get elapsedCycles() {
return this._machine.elapsedCycles;
}
/**
* Run until `count` more frames have been painted, stopping on the paint
* itself. A frame is 40000 cycles interlaced, 39936 not, and whatever a
* program driving the CRTC makes it, so stepping by cycles instead walks
* the sample point through the guest's frame.
*
* `completed` is false if a breakpoint fired, or the backstop ran out
* first.
*
* @param {number} [count=1] frames to advance
* @param {Object} [opts]
* @param {number} [opts.maxCycles] how long to wait on a machine that is not painting
* @returns {Promise<{framesRun: number, cyclesRun: number, completed: boolean}>}
*/
async runFrames(count = 1, { maxCycles } = {}) {
const cpu = this._machine.processor;
const backstop = maxCycles ?? count * BackstopSecondsPerFrame * cpu.model.cyclesPerSecond;
const startFrame = this._frameCount;
this._stopAtFrame = startFrame + count;
try {
const { cyclesRun } = await this.runFor(backstop);
const framesRun = this._frameCount - startFrame;
return { framesRun, cyclesRun, completed: framesRun >= count };
} finally {
this._stopAtFrame = Infinity;
}
}
/** Frames painted since the session was created; a hard reset does not zero it */
get frameCount() {
return this._frameCount;
}
/**
* Run until PC reaches targetAddr (like a breakpoint), or timeout.
*/
async runUntilAddress(addr, timeoutSecs = 30) {
await this._machine.runUntilAddress(addr, timeoutSecs);
}
/**
* Add a persistent breakpoint. Returns the breakpoint id.
* The hook stays active across run calls until removed.
* When the hook fires, cpu.stop() halts the current runFor.
* @param {"execute"|"read"|"write"} type
* @param {number} address
* @returns {number} breakpoint id
*/
addBreakpoint(type, address) {
const id = this._nextBreakpointId++;
const cpu = this._machine.processor;
const bp = { type, address, hit: false, id, value: undefined };
if (type === "execute") {
bp.hook = cpu.debugInstruction.add((pc) => {
if (pc === address) {
bp.hit = true;
return true;
}
});
} else if (type === "read") {
bp.hook = cpu.debugRead.add((addr, val) => {
if (addr === address) {
bp.hit = true;
bp.value = val;
return true;
}
});
} else if (type === "write") {
bp.hook = cpu.debugWrite.add((addr, val) => {
if (addr === address) {
bp.hit = true;
bp.value = val;
return true;
}
});
} else {
throw new Error(`Unknown breakpoint type: ${type}`);
}
this._breakpoints.set(id, bp);
return id;
}
/**
* Remove a breakpoint by id.
*/
removeBreakpoint(id) {
const bp = this._breakpoints.get(id);
if (!bp) throw new Error(`No breakpoint with id ${id}`);
bp.hook.remove();
this._breakpoints.delete(id);
}
/**
* Remove all breakpoints.
*/
clearBreakpoints() {
for (const bp of this._breakpoints.values()) {
bp.hook.remove();
}
this._breakpoints.clear();
}
/**
* Return the first breakpoint that was hit since the last reset, or null.
*/
hitBreakpoint() {
for (const bp of this._breakpoints.values()) {
if (bp.hit) {
const result = { id: bp.id, type: bp.type, address: bp.address };
if (bp.value !== undefined) result.value = bp.value;
return result;
}
}
return null;
}
/**
* Reset all hit flags (call before starting a new run).
*/
resetBreakpointHits() {
for (const bp of this._breakpoints.values()) {
bp.hit = false;
}
}
/**
* Load a disc image (absolute or relative path to an .ssd or .dsd file).
*
* We read the file ourselves rather than delegating to TestMachine.loadDisc,
* which goes through utils.loadData and mangles absolute paths by prepending "./".
*/
loadDisc(imagePath) {
const data = new Uint8Array(readFileSync(imagePath));
this._machine.processor.fdc.loadDisc(0, fdc.discFor(imagePath, data));
}
/**
* Put a disc in a drive by any reference the web page's URL accepts: a bare
* name from the built-in discs, `sth:`, `hfe:` or `bitshifters:` for the archives, or a URL.
* Returns the name of the image loaded and any others the archive held.
*/
async loadDiscImage(ref, drive = 0) {
const { name, data, ignored } = await this.mediaResolver().resolve("disc", ref);
this._machine.processor.fdc.loadDisc(drive, fdc.discFor(name, data));
return { name, ignored };
}
mediaResolver() {
if (!this._mediaResolver) {
this._mediaResolver = new MediaResolver();
this._mediaResolver.addSource("sth", (file) => new StairwayToHell().fetch(file));
this._mediaResolver.addSource("hfe", (path) => new BbcDiscArchive().fetch(path));
this._mediaResolver.addSource("bitshifters", (path) => new BitshiftersArchive().fetch(path));
}
return this._mediaResolver;
}
/**
* Return all VDU text elements captured so far.
*
* @param {Object} [opts]
* @param {boolean} [opts.clear=true] - If true (default), clear the buffer
* after returning it. Pass false to peek without consuming; the same
* elements will be returned again on the next call.
*
* Each element: { x, y, text, foreground, background, mode }
* Also includes a flat `screenText` reconstruction.
*/
drainOutput({ clear = true } = {}) {
this._capture.flush();
const elements = clear ? this._pendingOutput.splice(0) : [...this._pendingOutput];
return {
elements,
screenText: reconstructScreenText(elements),
};
}
/**
* What the memory map has paged in: `romsel`, the sideways bank at
* &8000 to &BFFF, and on a Master `acccon`, whose bit 2 puts shadow
* RAM at &3000 to &7FFF.
* @returns {{romsel: number, acccon?: number}}
*/
pagingState() {
const cpu = this._machine.processor;
const state = { romsel: cpu.romsel };
if (cpu.model.isMaster) state.acccon = cpu.acccon;
return state;
}
/**
* Runs `fn` with `bank` paged at &8000, or shadow RAM paged (or not)
* at &3000, putting the map back afterwards. Either left undefined
* leaves the map as the machine has it.
*/
_withPaging({ bank, shadow }, fn) {
const cpu = this._machine.processor;
const { romsel, acccon } = cpu;
if (bank !== undefined && (!Number.isInteger(bank) || bank < 0 || bank > 15))
throw new Error(`Bank ${bank} is not 0 to 15`);
if (shadow !== undefined && !cpu.model.isMaster) throw new Error("Only a Master has shadow RAM");
try {
if (bank !== undefined) cpu.romSelect(bank);
if (shadow !== undefined) cpu.writeAcccon(shadow ? acccon | AccconShadowBit : acccon & ~AccconShadowBit);
return fn();
} finally {
if (bank !== undefined) cpu.romSelect(romsel);
if (shadow !== undefined) cpu.writeAcccon(acccon);
}
}
/**
* Read `length` bytes from emulator memory starting at `address`, from
* whatever is paged in unless `bank` or `shadow` says otherwise.
* @param {number} address
* @param {number} [length=16]
* @param {Object} [opts]
* @param {number} [opts.bank] sideways bank to read at &8000 to &BFFF
* @param {boolean} [opts.shadow] on a Master, read shadow RAM (true) or main RAM (false) at &3000 to &7FFF
*/
readMemory(address, length = 16, { bank, shadow } = {}) {
return this._withPaging({ bank, shadow }, () => {
const bytes = [];
for (let i = 0; i < length; i++) {
bytes.push(this._machine.readbyte(address + i));
}
return bytes;
});
}
/**
* Write an array of byte values into emulator memory at `address`;
* `bank` and `shadow` pick where, as for readMemory.
*/
writeMemory(address, bytes, { bank, shadow } = {}) {
this._withPaging({ bank, shadow }, () => {
for (let i = 0; i < bytes.length; i++) {
this._machine.writebyte(address + i, bytes[i]);
}
});
}
/** Read the current 6502 CPU registers */
registers() {
const cpu = this._machine.processor;
return {
pc: cpu.pc,
a: cpu.a,
x: cpu.x,
y: cpu.y,
s: cpu.s, // stack pointer
p: cpu.p, // processor status
pcHex: `0x${cpu.pc.toString(16).toUpperCase().padStart(4, "0")}`,
aHex: `0x${cpu.a.toString(16).toUpperCase().padStart(2, "0")}`,
xHex: `0x${cpu.x.toString(16).toUpperCase().padStart(2, "0")}`,
yHex: `0x${cpu.y.toString(16).toUpperCase().padStart(2, "0")}`,
};
}
/**
* Capture the current screen as a PNG.
* Returns a Buffer containing a 1024×625 PNG (the full emulated display,
* including borders, matching what the browser renders).
*
* The active display area is roughly:
* x: leftBorder .. 1024-rightBorder
* y: topBorder .. 625-bottomBorder
*/
async screenshot() {
// Read from _completeFb8, the last fully-painted frame snapshotted in paint_ext.
// _fb8/_fb32 is the live render buffer (cleared and partially refilled each frame).
const { default: sharp } = await import("sharp");
return sharp(Buffer.from(this._completeFb8.buffer), {
raw: { width: FB_WIDTH, height: FB_HEIGHT, channels: 4 },
})
.png()
.toBuffer();
}
/**
* Capture only the active display area (no overscan borders), scaled to
* a more sensible pixel density. Returns a PNG Buffer.
*
* @param {Object} [opts]
* @param {number} [opts.scale=2] - integer scale factor
*/
async screenshotActive(opts = {}) {
const scale = opts.scale ?? 2;
const v = this._video;
const left = v.leftBorder;
const top = v.topBorder;
const right = v.rightBorder;
const bottom = v.bottomBorder;
const w = FB_WIDTH - left - right;
const h = FB_HEIGHT - top - bottom;
const { default: sharp } = await import("sharp");
return sharp(Buffer.from(this._completeFb8.buffer), {
raw: { width: FB_WIDTH, height: FB_HEIGHT, channels: 4 },
})
.extract({ left, top, width: w, height: h })
.resize(w * scale, h * scale, { kernel: "nearest" }) // nearest-neighbour keeps pixels crisp
.png()
.toBuffer();
}
/** Free any resources (currently just clears the framebuffer) */
destroy() {
this._fb8.fill(0);
this._pendingOutput = [];
}
}
// ---------------------------------------------------------------------------
// Helpers
// ---------------------------------------------------------------------------
/**
* Reconstruct a flat text representation from the captured VDU elements.
* Builds a 2D grid of characters and returns it as a newline-separated string.
*/
function reconstructScreenText(elements) {
if (elements.length === 0) return "";
// Find bounds
let maxX = 0;
let maxY = 0;
for (const el of elements) {
const endX = el.x + el.text.length;
if (endX > maxX) maxX = endX;
if (el.y > maxY) maxY = el.y;
}
// Fill grid
const rows = Array.from({ length: maxY + 1 }, () => Array(maxX + 1).fill(" "));
for (const el of elements) {
for (let i = 0; i < el.text.length; i++) {
const col = el.x + i;
if (col < rows[el.y].length) {
rows[el.y][col] = el.text[i];
}
}
}
return rows.map((r) => r.join("").trimEnd()).join("\n");
}
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