Press n or j to go to the next uncovered block, b, p or k for the previous block.
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// where it is to go, and run forward to there exactly. Snapshots leave out what the host gives the machine (keys,
// FIRE buttons, BREAK, a debugger's edits) and what the machine reads from the host as it runs (the analogue
// channels, the clock, the touchscreen), so an InputLog records both as they happen, and a replay puts each back
// where it went in or was read.
import { applyInput, cycleCount, stateHash } from "./lockstep.js";
import { tickCycles } from "./emulation-tick.js";
import { NoReplayHooks } from "./6502.js";
import { RamStat, RomStat, viewedByte } from "./paging.js";
/** How much history the page keeps: snapshots at each of the last `recent` frames, and one a second for `seconds`. */
export const PageHistory = Object.freeze({ recent: 3, seconds: 30 });
// How far back step back over looks for the call it is to land on, past which the wait is not worth it.
const LongestCallSearchSeconds = 2;
const InterruptPushes = 3;
const EmptyStack = 0xff;
const KeepsHistory =
"the machine keeps its history once it has run a frame since it started, was reset or had its state replaced";
const NothingToStepBackTo = `There is nothing to step back to: ${KeepsHistory}.`;
const NothingToSearch = `There is no history to search back through: ${KeepsHistory}.`;
const NotRepeated = "Step back could not repeat the machine's run exactly, so the machine is left where it was.";
const NoCallFound = `Step back over found no call this returned from in the last ${LongestCallSearchSeconds} seconds.`;
const NothingToStepOutOf = "There is no call or interrupt to step back out of: the stack is empty (S is &FF).";
const NothingToContinueTo = "There is no breakpoint or watch that stops the machine to reverse continue to.";
const TooFarBack = "That is further back than the machine keeps its history.";
const NotBehind = "That is not before where the machine is now.";
const IsRom = "That is ROM, which a write leaves as it is.";
const NotRepeatedHere = "The search could not repeat the machine's run since its newest snapshot exactly.";
const CannotSearchPast = "The search cannot go back past";
const MovedOn = "The machine moved on before the search back finished.";
const Unrepeated = "a stretch of the run it could not repeat exactly";
const MidInstruction = "an input that came part way through an instruction";
// S counts down and wraps, so "not deeper" is a difference of under half the page, either way round $00.
export function notDeeper(s, startS) {
return ((s - startS) & 0xff) < 0x80;
}
const MicrosecondsPerSecond = 1e6;
const MillisecondsPerSecond = 1e3;
/** `seconds` in the unit that suits it, to a tenth. */
export function durationText(seconds) {
if (seconds * MillisecondsPerSecond < 1) return `${(seconds * MicrosecondsPerSecond).toFixed(1)} \u00b5s`;
Eif (seconds < 1) return `${(seconds * MillisecondsPerSecond).toFixed(1)} ms`;
return `${seconds.toFixed(1)} s`;
}
export const snapshotCycle = (cpu, snapshot) =>
snapshot.cycleSeconds * cpu.model.cyclesPerSecond + snapshot.currentCycles;
/** Runs `generator` to its end, returning what it returns. */
export function finished(generator) {
for (;;) {
const { done, value } = generator.next();
if (done) return value;
}
}
/**
* Runs `run` with `video` painting nothing to the screen, as the benchmark page's video-only pass does, so that the
* screen keeps showing the machine as it stands while its past is replayed.
*/
function withoutPainting(video, run) {
const paint = video.paint_ext;
video.paint_ext = () => {};
try {
return run();
} finally {
video.paint_ext = paint;
}
}
// Between executes the CPU has reached its cycle target or been stopped short of it; inside one, as a scheduled
// task or a read, write or interrupt hook runs, it has done neither; an instruction hook runs between instructions.
const insideExecute = (cpu) => !cpu.halted && cpu.currentCycles < cpu.targetCycles && !cpu.debugInstruction.dispatching;
function hostInputs(cpu) {
const { gamepad, mouse } = cpu.sysvia.fireButtons();
return { keyboard: cpu.keyboardInterface.keyboardState(), gamepad, mouse, resetting: !cpu.resetLine };
}
/** What the host holds once `input` has gone in, from `host`, what it held before. */
function withInput(host, input) {
switch (input.kind) {
case "keyboard":
return { ...host, keyboard: input.state };
case "gamepadFire":
return { ...host, gamepad: [input.button1, input.button2] };
case "joystickButton":
return {
...host,
mouse: host.mouse.map((pressed, button) => (button === input.button ? input.pressed : pressed)),
};
case "break":
return { ...host, resetting: input.down };
default:
return host;
}
}
/** The inputs that take the host from holding `from` to holding `to`. */
function hostChanges(from, to) {
const changes = [];
Iif (JSON.stringify(from.keyboard) !== JSON.stringify(to.keyboard)) {
changes.push({ kind: "keyboard", state: to.keyboard });
}
Iif (from.gamepad.some((pressed, button) => pressed !== to.gamepad[button])) {
changes.push({ kind: "gamepadFire", button1: to.gamepad[0], button2: to.gamepad[1] });
}
to.mouse.forEach((pressed, button) => {
Iif (pressed !== from.mouse[button]) changes.push({ kind: "joystickButton", button, pressed });
});
Iif (from.resetting !== to.resetting) changes.push({ kind: "break", down: to.resetting });
return changes;
}
// Before the machine's own restore, as restoreSessionSnapshot puts the keys back, so that its VIA scans these.
function restoreHostInputs(cpu, { keyboard, gamepad, mouse, resetting }) {
cpu.keyboardInterface.restoreKeyboard(keyboard);
cpu.sysvia.setGamepadFire(...gamepad);
mouse.forEach((pressed, button) => cpu.sysvia.setJoystickButton(button, pressed));
cpu.setReset(resetting);
}
// As far as `cycle`, an instruction boundary, in the page's ticks as everything else that runs execute does; false
// if something stopped the machine short of it.
function runTo(cpu, cycle) {
const longest = tickCycles(cpu.model.cyclesPerSecond);
while (cycleCount(cpu) < cycle) {
const end = Math.min(cycle, cycleCount(cpu) + longest);
cpu.targetCycles = end - cpu.cycleSeconds * cpu.model.cyclesPerSecond;
Iif (!cpu.execute(0)) return false;
}
return true;
}
/** The samples a replay hands the machine, in place of the host, each as it was when the original run read it. */
class SampleReplay {
constructor(samples, from, values) {
this.samples = samples;
this.next = samples.findIndex(({ at }) => at > from);
Eif (this.next < 0) this.next = samples.length;
this.values = values;
}
// A read the original run never made, as in a replay gone its own way, gets the host's value, and the check
// at the end of the replay finds it out.
read(key, at, live) {
while (this.next < this.samples.length && this.samples[this.next].at <= at) {
const { key: read, value } = this.samples[this.next++];
this.values.set(read, value);
}
return this.values.has(key) ? this.values.get(key) : live;
}
}
/**
* What the host gave the machine and what the machine read from the host, from where a replay can start. Inputs
* are recorded with the cycle they went in at, between executes, as `{ at, input }` in the shape `applyInput`
* takes; samples with the cycle they were read at, only as they change; and refusals, `{ at, refusal }`, where
* something went in that no replay can put back, which no replay crosses. Every device the host reaches holds it
* as `inputLog`, and while it replays it gives them the samples instead of the host and records nothing.
*/
export class InputLog {
constructor(cpu) {
this.cpu = cpu;
this.latestSamples = new Map();
this.sampleReplay = null;
this.recording = true;
this.applyingInput = false;
for (const device of this._devices()) device.inputLog = this;
this.restart();
}
_devices() {
const { cpu } = this;
const { keyboardInterface, sysvia, adconverter, touchScreen, acia, fdc } = cpu;
return [cpu, keyboardInterface, sysvia, adconverter, touchScreen, sysvia.cmos, acia, ...fdc.drives];
}
/** Stops every device the host reaches recording into this log, so that nothing keeps it growing. */
detach() {
for (const device of this._devices()) device.inputLog = null;
}
/** Forgets everything recorded, the machine's state having been replaced; replays start from here on. */
restart() {
this.inputs = [];
this.samples = [];
this.base = hostInputs(this.cpu);
this.baseSamples = new Map(this.latestSamples);
}
get isEmpty() {
return this.inputs.length === 0 && this.samples.length === 0;
}
record(input) {
if (!this.recording) return;
Iif (insideExecute(this.cpu)) this.refuse(MidInstruction);
else this.inputs.push({ at: cycleCount(this.cpu), input });
}
/** Notes that something went in here that no replay can put back, `reason` naming it for the refusal. */
refuse(reason) {
Eif (this.recording) this.inputs.push({ at: cycleCount(this.cpu), refusal: reason });
}
/** What the machine reads for `key` from the host, which said `value`. */
sample(key, value) {
if (this.sampleReplay) return this.sampleReplay.read(key, cycleCount(this.cpu), value);
if (this.recording && this.latestSamples.get(key) !== value) {
this.latestSamples.set(key, value);
this.samples.push({ at: cycleCount(this.cpu), key, value });
}
return value;
}
/** What the host held at `cycle`, before any input that went in there. */
hostAt(cycle) {
let host = this.base;
for (const { at, input } of this.inputs) {
if (at >= cycle) break;
Iif (input) host = withInput(host, input);
}
return host;
}
/** The latest of each sample read up to `cycle`. */
samplesAt(cycle) {
const values = new Map(this.baseSamples);
for (const { at, key, value } of this.samples) {
if (at > cycle) break;
values.set(key, value);
}
return values;
}
/** The first refusal from `from` to `to`, both included, or null. */
refusalBetween(from, to) {
return this.inputs.find(({ at, refusal }) => refusal && at >= from && at <= to)?.refusal ?? null;
}
/** Folds into where a replay starts everything before `cycle`, from where no replay starts any more. */
trimBefore(cycle) {
const firstInput = this.inputs.findIndex(({ at }) => at >= cycle);
if (firstInput !== 0) {
this.base = this.hostAt(cycle);
this.inputs = firstInput < 0 ? [] : this.inputs.slice(firstInput);
}
const firstSample = this.samples.findIndex(({ at }) => at > cycle);
if (firstSample !== 0) {
this.baseSamples = this.samplesAt(cycle);
this.samples = firstSample < 0 ? [] : this.samples.slice(firstSample);
}
}
/** Forgets what went in after `cycle`, the machine having gone back there, and carries on from what it read. */
forgetAfter(cycle) {
this.inputs = this.inputs.filter(({ at }) => at <= cycle);
this.samples = this.samples.filter(({ at }) => at <= cycle);
this.latestSamples = this.samplesAt(cycle);
}
/** Runs `run` recording nothing, as when the machine is put back as it was. */
withoutRecording(run) {
this.recording = false;
try {
return run();
} finally {
this.recording = true;
}
}
/**
* Puts the machine back to `snapshot` and runs it to `to` as a replay (as `asReplay` runs one, watched by
* `hooks`), putting each input back at its cycle, those at `to` too if `inputsAtTo`, with
* `applyingInput` set as each goes in. Returns the hash of the machine as the snapshot put it, or null if the
* replay did not reach an input's cycle or `to` exactly.
*/
replay(snapshot, to, inputsAtTo, hooks) {
const { cpu } = this;
const from = snapshotCycle(cpu, snapshot);
this.recording = false;
this.sampleReplay = new SampleReplay(this.samples, from, this.samplesAt(from));
try {
restoreHostInputs(cpu, this.hostAt(from));
cpu.restoreState(snapshot);
cpu.debugInstruction.forgetStop();
const startHash = stateHash(cpu);
const reached = cpu.asReplay(hooks, () => {
for (const { at, input } of this.inputs) {
if (at < from || !input) continue;
if (at > to || (at === to && !inputsAtTo)) break;
Iif (!runTo(cpu, at) || cycleCount(cpu) !== at) return false;
this.applyingInput = true;
try {
applyInput(cpu, input);
} finally {
this.applyingInput = false;
}
}
return runTo(cpu, to) && cycleCount(cpu) === to;
});
return reached ? startHash : null;
} finally {
this.sampleReplay = null;
this.recording = true;
}
}
}
/**
* Where a step back lands, worked out from the instructions replays pass the start of, a window at a time from
* the newest. Back one, it is the last instruction of the first window. Back over, it is the same unless that
* instruction returned to here (a return with the stack shallower after it); then it is the last instruction
* before it at a stack no deeper than here, the call that return came back from, in whichever window has one, as
* far back as is worth the wait.
*/
class Landing {
constructor(cpu, over) {
this.cpu = cpu;
this.over = over;
this.s = cpu.s;
this.seekingCall = false;
this.searchFrom = cycleCount(cpu) - LongestCallSearchSeconds * cpu.model.cyclesPerSecond;
this.hooks = { ...NoReplayHooks, instruction: (_pc, opcode) => this.passing(opcode) };
}
searches(from) {
return !this.seekingCall || from >= this.searchFrom;
}
startWindow() {
this.last = null;
this.lastS = 0;
this.lastOpcode = 0;
this.notDeeperBeforeLast = null;
}
passing(opcode) {
if (this.last !== null && notDeeper(this.lastS, this.s)) this.notDeeperBeforeLast = this.last;
this.last = cycleCount(this.cpu);
this.lastS = this.cpu.s;
this.lastOpcode = opcode;
}
/** The cycle to land on from the window just replayed, or null to look in the one before it. */
inWindow() {
if (this.seekingCall)
return this.last !== null && notDeeper(this.lastS, this.s) ? this.last : this.notDeeperBeforeLast;
const returnedHere =
this.cpu.disassembler.describeOpcode(this.lastOpcode).flow === "return" &&
this.s !== this.lastS &&
notDeeper(this.s, this.lastS);
if (!this.over || !returnedHere) return this.last;
this.seekingCall = true;
return this.notDeeperBeforeLast;
}
}
/** A step back to `cycle`, an instruction boundary, landed on from the window that holds it. */
class Arrival {
constructor(cycle) {
this.cycle = cycle;
this.from = 0;
this.hooks = NoReplayHooks;
}
searches() {
return true;
}
startWindow(from) {
this.from = from;
}
inWindow() {
return this.from <= this.cycle ? this.cycle : null;
}
}
/**
* The last write in a window to the byte viewedByte gives as `{ stat, offset }`: that byte of RAM, however the CPU
* paged it there at the time, or else the device register at `address`.
*/
class LastWrite {
constructor(cpu, log, address, { stat, offset }) {
let pc = 0;
let started = 0;
this.found = null;
const instruction = (at) => {
pc = at;
started = cycleCount(cpu);
};
const write = (written, value) => {
const page = cpu.memStatOffset + (written >>> 8);
const writtenStat = cpu.memStat[page];
if (writtenStat !== stat) return;
if (stat === RamStat ? cpu.memLook[page] + written !== offset : written !== address) return;
const byte = value & 0xff;
this.found = log.applyingInput
? { pc: null, cycle: cycleCount(cpu), value: byte }
: { pc, cycle: started, value: byte };
};
this.hooks = { ...NoReplayHooks, instruction, write };
}
searches() {
return true;
}
startWindow() {
this.found = null;
}
inWindow() {
return this.found;
}
}
/**
* Where a step back out lands: the latest instruction that entered a routine, a JSR or BRK or one an interrupt was
* taken after, whose stack is shallower than here and than at every instruction after it. Each window keeps only
* the instructions shallower than every one after them in it, the only ones it could be.
*/
class OutLanding {
constructor(cpu) {
this.cpu = cpu;
this.s = cpu.s;
this.highestAfter = 0;
this.hooks = {
...NoReplayHooks,
instruction: (_pc, opcode) => this.passing(opcode),
// Entered from the stack the instruction before left, which the interrupt pushed three bytes onto.
interrupt: () =>
this._keep(this.shallower.at(-1).cycle, this._height((this.cpu.s + InterruptPushes) & 0xff), true),
};
}
searches() {
return true;
}
// How many bytes shallower than here the stack is at `s`, negative for deeper.
_height(s) {
const above = (s - this.s) & 0xff;
return above < 0x80 ? above : above - 0x100;
}
startWindow() {
this.shallower = [];
}
passing(opcode) {
const { flow } = this.cpu.disassembler.describeOpcode(opcode);
this._keep(cycleCount(this.cpu), this._height(this.cpu.s), flow === "call" || flow === "interrupt");
}
_keep(cycle, height, enters) {
while (this.shallower.length && this.shallower.at(-1).height <= height) this.shallower.pop();
this.shallower.push({ cycle, height, enters });
}
inWindow() {
const entry = this.shallower.findLast(({ enters, height }) => enters && height > this.highestAfter);
if (entry) return entry.cycle;
this.highestAfter = Math.max(this.highestAfter, this.shallower[0].height);
return null;
}
}
/**
* Where a reverse continue lands: where the machine would have stopped, running forward, at the newest breakpoint
* or watch hit before now. An instruction breakpoint stops before its instruction; a watch, or an interrupt
* breakpoint, at the instruction after the access, or after the interrupt is taken.
*/
class HitLanding {
constructor(cpu) {
this.cpu = cpu;
this.now = cycleCount(cpu);
this.armed = Object.values(this._tests()).some((test) => test !== null);
this.found = null;
}
searches() {
return true;
}
_tests() {
return this.cpu.breakpoints.replayHooks((access, address) => this._hit(access, address));
}
// Afresh for each window, as a test for a change must not take the end of a later window for what came before.
startWindow() {
const tests = this._tests();
this.hooks = {
...tests,
instruction: (pc, opcode) => {
this._passing(pc);
tests.instruction?.(pc, opcode);
},
};
this.last = null;
this.next = null;
this.read = null;
}
// The CPU reads an instruction's opcode just before it starts, so a hit on the read of this one's stops the
// machine after it, as an access by the instruction before stops it here.
_passing(pc) {
this.at = cycleCount(this.cpu);
const fetched = this.read?.address === pc;
const here = fetched ? this.read.before : this.next;
Iif (here) this.last = { ...here, cycle: this.at };
this.next = fetched ? { stoppedBefore: false } : null;
this.read = null;
}
_hit(access, address) {
if (access === "execute") {
this.last = { cycle: this.at, stoppedBefore: true };
return;
}
const before = this.next;
this.next = { stoppedBefore: before?.stoppedBefore || access === "interrupt" };
this.read = access === "read" ? { address, before } : null;
}
// A stop after the window's last instruction falls where the window ends, which, the window ending now, is
// where the machine is.
inWindow(to) {
if (this.next && to < this.now) this.last = { ...this.next, cycle: to };
this.found = this.last;
return this.last?.cycle ?? null;
}
}
/**
* What the debugger can step back through: the snapshots kept of the machine since its state was last replaced,
* and the input log back to the oldest of them. Dispatches "landed", with the snapshots it forgot as
* `detail.forgotten`, once a step back has forgotten everything after where it landed, for whoever else keeps them.
*/
export class ReplayHistory extends EventTarget {
constructor(cpu) {
super();
this.cpu = cpu;
this.log = new InputLog(cpu);
this.kept = new Set();
}
/** Takes `snapshot` as one a replay can start from, in place of `replacing`, if any, whose storage it took. */
taken(snapshot, replacing) {
this.kept.delete(replacing);
const cycle = snapshotCycle(this.cpu, snapshot);
Iif ([...this.kept].some((kept) => snapshotCycle(this.cpu, kept) > cycle)) this.restart();
this.kept.add(snapshot);
}
/** Forgets every snapshot and input so far, the machine's state having been replaced. */
restart() {
this.kept.clear();
this.log.restart();
}
/** Forgets inputs from before the oldest snapshot a replay can start from. */
trim() {
Eif (this.log.isEmpty) return;
const [oldest] = this.snapshots();
if (oldest) this.log.trimBefore(snapshotCycle(this.cpu, oldest));
}
/** The snapshots a replay can start from, oldest first. */
snapshots() {
const cycle = (snapshot) => snapshotCycle(this.cpu, snapshot);
return [...this.kept].sort((a, b) => cycle(a) - cycle(b));
}
_earlier(now) {
return this.snapshots().filter((snapshot) => snapshotCycle(this.cpu, snapshot) < now);
}
/** Why `what`, a replay of the machine's history, cannot be done from where it is; `nothing` if it has none. */
_unavailable(what, nothing) {
const { cpu } = this;
if (cpu.econet) return `${what} is not available with Econet, whose network a replay cannot repeat.`;
if (cpu.tapeInterface.motorOn) return `${what} is not available while the cassette motor runs.`;
return this._earlier(cycleCount(cpu)).length ? null : nothing;
}
/** Why the machine cannot step back from where it is, or null if it can. */
refusal() {
const { cpu } = this;
const unavailable = this._unavailable("Step back", NothingToStepBackTo);
if (unavailable) return unavailable;
const now = cycleCount(cpu);
const crossing = this.log.refusalBetween(snapshotCycle(cpu, this._earlier(now).at(-1)), now);
return crossing && `Step back cannot go back past ${crossing}.`;
}
/**
* Replays the stretches between the snapshots before now, newest first, each checked to end on the machine it
* is replayed towards (the state now or the next snapshot's), until `seeker` finds in one what it looks for,
* yielding after each stretch that does not have it. A seeker replays each stretch with its `hooks`, is told of
* each with `startWindow(from)`, says with `inWindow(to)` what it found there or null, and with `searches(from)`
* whether a stretch from `from` is worth replaying. Returns `{ found, snapshot, reached, stoppedBy }`: what it
* found, or null, and the snapshot of the stretch it was found in; the cycle the search reached back to; and why
* it went no further, null if it ran out of stretches or `seeker` wanted none older: something no replay
* crosses, or Unrepeated. Leaves the machine at the end of whichever stretch it replayed last.
*/
*_searchBack(seeker) {
const { cpu, log } = this;
let [to, hash, inputsAtTo] = [cycleCount(cpu), stateHash(cpu), true];
for (const snapshot of this._earlier(to).reverse()) {
const from = snapshotCycle(cpu, snapshot);
// A rewind snapshot is a copy of a frame snapshot, at the same cycle, and has nothing to replay.
if (from === to) continue;
if (!seeker.searches(from)) break;
const crossing = log.refusalBetween(from, to);
if (crossing) return { found: null, snapshot: null, reached: to, stoppedBy: crossing };
seeker.startWindow(from);
const fromHash = log.replay(snapshot, to, inputsAtTo, seeker.hooks);
if (fromHash === null || stateHash(cpu) !== hash)
return { found: null, snapshot: null, reached: to, stoppedBy: Unrepeated };
const found = seeker.inWindow(to);
if (found !== null) return { found, snapshot, reached: from, stoppedBy: null };
[to, hash, inputsAtTo] = [from, fromHash, false];
yield;
}
return { found: null, snapshot: null, reached: to, stoppedBy: null };
}
_original() {
const { cpu } = this;
const { memStatOffset } = cpu;
return { state: cpu.snapshotState(), host: hostInputs(cpu), picture: cpu.video.fb32.slice(), memStatOffset };
}
/**
* Puts the machine, the host's inputs and the picture back as `_original` kept them, with the half of the paging
* tables the last instruction's fetch chose, which a snapshot leaves out.
*/
_putBack({ state, host, picture, memStatOffset }) {
const { cpu } = this;
this.log.withoutRecording(() => {
restoreHostInputs(cpu, host);
cpu.restoreState(state);
});
cpu.video.fb32.set(picture);
cpu.memStatOffset = memStatOffset;
}
// Steps back to the cycle `seeker` finds, or returns why it could not, `notFound` if no stretch held one.
_stepBackFinding(seeker, notFound) {
return finished(
this._steppingBack(seeker, (stoppedBy) => {
Iif (stoppedBy === Unrepeated) return NotRepeated;
return stoppedBy ? `Step back cannot go back past ${stoppedBy}.` : notFound;
}),
);
}
/**
* Runs `_searchBack(seeker)` a stretch at a time, painting none of it, putting the machine back as `original`
* keeps it between stretches and yielding there. Returns what the search returns, with the machine where its
* last stretch left it, or `{ movedOn: true }` if the machine has moved on when the search resumes.
*/
*_searchingAway(seeker, original) {
const { cpu } = this;
const [now, nowHash] = [cycleCount(cpu), stateHash(cpu)];
const search = this._searchBack(seeker);
for (;;) {
let step;
try {
step = withoutPainting(cpu.video, () => search.next());
} catch (e) {
this._putBack(original);
throw e;
}
if (step.done) return step.value;
this._putBack(original);
yield;
if (cycleCount(cpu) !== now || stateHash(cpu) !== nowHash) return { movedOn: true };
}
}
/**
* Steps back to the cycle `seeker` finds, searching back a stretch at a time as lastWrite does, painting none of
* it, and yielding between stretches with the machine as it was; if the machine has moved on when it resumes,
* it stops. Returns why it could not, having left the machine and its picture as they were, or null. If no
* stretch held what it seeks, `unfound(stoppedBy, searched)` says why, with `stoppedBy` what no replay crosses
* (Unrepeated among them), or null where the history ends, and `searched` how many cycles back from now it
* looked.
*/
*_steppingBack(seeker, unfound) {
const refused = this.refusal();
if (refused) return refused;
const now = cycleCount(this.cpu);
const original = this._original();
const { movedOn, found, snapshot, reached, stoppedBy } = yield* this._searchingAway(seeker, original);
if (movedOn) return MovedOn;
let landed = false;
try {
Iif (stoppedBy === Unrepeated && reached === now) return NotRepeated;
if (found === null) return unfound(stoppedBy, now - reached);
Iif (this.log.replay(snapshot, found, true, NoReplayHooks) === null) return NotRepeated;
landed = true;
this._landedAt(found, original.host);
return null;
} finally {
if (!landed) this._putBack(original);
}
}
/** Says that `what` was found nowhere in the cycles searched, and why the search stopped, as `unfound` does. */
_searchedFor(what) {
return (stoppedBy, searched) => {
const ago = `${searched} cycles (${durationText(searched / this.cpu.model.cyclesPerSecond)})`;
const why = stoppedBy ? `cannot go back past ${stoppedBy}` : "that is as far back as the history goes";
return `${what} in the last ${ago}, and ${why}.`;
};
}
/**
* Steps the machine back one instruction, or with `over` back over the call the instruction before returned
* from, by replaying from the newest snapshot before it (older ones too, for a call further back). Each
* stretch replayed must end on the machine it is replayed towards, the state now or the next snapshot, or
* nothing is trusted. What the host holds now (keys, FIRE buttons, BREAK) it holds where the machine lands.
* Returns why it could not, having left the machine and its picture as they were, or null.
*/
stepBack(over) {
return this._stepBackFinding(new Landing(this.cpu, over), NoCallFound);
}
/**
* Steps the machine back to the call or interrupt that entered the routine it is in, a stretch at a time as
* `_steppingBack` does. With the stack empty, as at the top level of a program that reset it, there is none.
*/
*stepBackOut() {
if (this.cpu.s === EmptyStack) return NothingToStepOutOf;
return yield* this._steppingBack(
new OutLanding(this.cpu),
this._searchedFor("Step back out found no call or interrupt that entered this routine"),
);
}
/**
* Steps the machine back to where it would have stopped at the newest breakpoint or watch hit before now, a
* stretch at a time as `_steppingBack` does. Every hit counts, whatever a breakpoint's hit count, as how many
* hits it had at each moment is not kept.
*/
*reverseContinue() {
const landing = new HitLanding(this.cpu);
if (!landing.armed) return NothingToContinueTo;
const refusal = yield* this._steppingBack(
landing,
this._searchedFor("Reverse continue found no breakpoint or watch hit"),
);
// Stopped at a breakpoint as a forward run would be, so that none stops the machine there again on resuming.
if (refusal === null && landing.found.stoppedBefore) this.cpu.debugInstruction.rememberUnseenStop();
return refusal;
}
/** Steps the machine back to `cycle`, an instruction boundary since its oldest snapshot, as stepBack does. */
stepBackTo(cycle) {
if (cycle >= cycleCount(this.cpu)) return NotBehind;
return this._stepBackFinding(new Arrival(cycle), TooFarBack);
}
/**
* Searches for the last write to the byte `view` shows at `address` (see LastWrite), by replaying its
* history back from now a stretch at a time, as a step back does, painting none of it. Yields between
* stretches, with the machine as it was, so that a long search can let the page go on; if the machine has moved
* on when it resumes, it stops.
* Returns `{ refusal }` when it cannot search (ROM, which no write changes, among the reasons), or else
* `{ write, searched, stoppedBy }`: `write` is `{ pc, cycle, value }`, `cycle` where the instruction at `pc`
* started, or with `pc` null where an input such as a memory panel edit wrote it, or null if nothing wrote it in
* the `searched` cycles back from now; `stoppedBy` is why the search went back no further (as `_searchBack`
* gives it), or null where the history ends. Leaves the machine as it was.
*/
*lastWrite(address, view) {
const refusal = this._unavailable("Searching back", NothingToSearch);
if (refusal) return { refusal };
const { cpu, log } = this;
const target = viewedByte(cpu, view, address);
if (target.stat === RomStat) return { refusal: IsRom };
const now = cycleCount(cpu);
const original = this._original();
const { movedOn, found, reached, stoppedBy } = yield* this._searchingAway(
new LastWrite(cpu, log, address, target),
original,
);
if (movedOn) return { refusal: MovedOn };
this._putBack(original);
if (stoppedBy && reached === now) {
return { refusal: stoppedBy === Unrepeated ? NotRepeatedHere : `${CannotSearchPast} ${stoppedBy}.` };
}
return { write: found, searched: now - reached, stoppedBy };
}
// What came after `cycle` was a future the machine has left, and runs from here make their own.
_landedAt(cycle, holding) {
this.log.forgetAfter(cycle);
const forgotten = new Set([...this.kept].filter((snapshot) => snapshotCycle(this.cpu, snapshot) > cycle));
for (const snapshot of forgotten) this.kept.delete(snapshot);
for (const input of hostChanges(hostInputs(this.cpu), holding)) {
this.log.record(input);
this.log.withoutRecording(() => applyInput(this.cpu, input));
}
this.dispatchEvent(new CustomEvent("landed", { detail: { forgotten } }));
}
}
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