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// bytes of user storage. Storage byte 11 (= CMOS address 25 = 0x19) holds
// the BBC Master DFS configuration byte whose bits [1:0] are the WD1770 step
// rate (*CONFIGURE FDRIVE): 0=6ms 1=12ms 2=20ms 3=30ms.
// The correct default is FDRIVE 0 (6ms, value 0xc8). The previous default
// 0xca had bits[1:0]=0b10 (20ms), which caused disc-streaming demos such as
// STNICC-beeb to hang on the Master 128 because the WD1770 seek overran the
// vsync window. Confirmed by @tom-seddon (b2 emulator):
// https://github.com/mattgodbolt/jsbeeb/issues/576
const defaultCmos = Object.freeze([
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xfe, 0x00, 0xeb, 0x00,
0xc9, 0xff, 0xff, 0x12, 0x00, 0x17, 0xc8, 0x1e, 0x05, 0x00, 0x35, 0xa6, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
]);
// A store saved before it held the whole chip: its first 48 bytes, longer if a program wrote past them.
const OldestStoreBytes = 48;
/** A copy of `bytes` as a whole store, the defaults filling what an older page's lacks; throws on any other shape. */
function fullStore(bytes) {
if (!Array.isArray(bytes) || bytes.length < OldestStoreBytes || bytes.length > defaultCmos.length)
throw new Error(`the settings are not ${OldestStoreBytes} to ${defaultCmos.length} bytes`);
return Array.from(defaultCmos, (byte, address) => bytes[address] ?? byte);
}
// The RTC holds a two-digit year and MOS 3.20 prints it after a fixed century (LDA #&19 at &9880 in ROM 15);
// the ROM jsbeeb ships has that byte patched to &20 (#362), so every year it shows is 20yy.
const MosCentury = 2000;
function toBcd(value) {
return parseInt(value.toString(10), 16);
}
function fromBcd(value) {
return parseInt(value.toString(16), 10);
}
const TimeRegisters = Object.freeze({
0: { limit: 60, get: (time) => time.getSeconds(), set: (time, value) => time.setSeconds(value) },
2: { limit: 60, get: (time) => time.getMinutes(), set: (time, value) => time.setMinutes(value) },
4: { limit: 24, get: (time) => time.getHours(), set: (time, value) => time.setHours(value) },
});
function isBcdBelow(value, limit) {
return value >> 4 < 10 && (value & 0x0f) < 10 && fromBcd(value) < limit;
}
export { defaultCmos };
// A shared session (src/lockstep.js) runs the same machine on several computers in step, one of them hosting.
// The session clock holds the host's local time as if it were UTC and is read and set through this view, so
// every computer shows the host's time, whatever its own time zone.
function utcView(date) {
return {
getSeconds: () => date.getUTCSeconds(),
getMinutes: () => date.getUTCMinutes(),
getHours: () => date.getUTCHours(),
getDay: () => date.getUTCDay(),
getDate: () => date.getUTCDate(),
getMonth: () => date.getUTCMonth(),
getFullYear: () => date.getUTCFullYear(),
setSeconds: (value) => date.setUTCSeconds(value),
setMinutes: (value) => date.setUTCMinutes(value),
setHours: (value) => date.setUTCHours(value),
setFullYear: (year, month, day) => date.setUTCFullYear(year, month, day),
getTime: () => date.getTime(),
};
}
/**
* CMOS persistence backed by a browser storage object, which can be unavailable, full or holding
* something other than what was last saved.
*
* @param {function(): Storage} getStorage typically `() => window.localStorage`. Reading that
* property is itself what throws when a page is refused storage, so it happens per call, inside
* the try.
* @param {function(*)} onSaveFailure called with the error the first time a save fails
*/
export function localStoragePersistence(getStorage, onSaveFailure) {
let saveFailureReported = false;
return {
load() {
try {
const stored = getStorage().cmosRam;
if (!stored) return null;
return fullStore(JSON.parse(stored));
} catch (error) {
console.log(`Unable to read the stored CMOS settings: ${error?.message ?? error}`);
return null;
}
},
save(data) {
try {
getStorage().cmosRam = JSON.stringify(data);
} catch (error) {
console.log(`Unable to store the CMOS settings: ${error?.message ?? error}`);
if (saveFailureReported) return;
saveFailureReported = true;
onSaveFailure(error);
}
},
};
}
export class Cmos {
constructor(persistence, cmosOverride, econet) {
this.store = persistence ? persistence.load() : null;
this.persistence = persistence;
this.enabled = false;
this.isRead = false;
this.addressSelect = false;
this.dataSelect = false;
this.cmosAddr = 0;
this.now = () => Date.now();
// A replay repeats writes the machine made, or makes some it never will (a rewind preview), so it keeps none.
this.replaying = () => false;
this.utc = false;
this.timeOffset = 0;
// The 146818 keeps the day, month and year in separate registers and checks none of them, so bytes that
// do not name a real day are held as written until they do.
this.heldDate = null;
// Likewise a seconds, minutes or hours byte that is not a time, keyed by register, while the clock runs on.
this.heldTime = {};
this.beforeSession = null;
/** @type {import("./replay.js").InputLog | null} */
this.inputLog = null;
if (!this.store) {
this.store = [...defaultCmos];
}
if (cmosOverride) {
this.store = cmosOverride(this.store);
}
if (econet) {
this.store[0xe] = econet.stationId;
Iif (this.store[0xf] === 0) {
// Catch an invalid FS configuration setting (possibly as a result of using a prior version that didn't set a default of 254 in CMOS)
this.store[0xf] = 254;
}
}
// What the machine has written, which a restore leaves alone: the settings a page loads next.
this.kept = [...this.store];
this.save();
}
save() {
this.persistence?.save(this.kept);
}
keep(address, value) {
if (!this.persistence || this.replaying()) return;
this.kept[address] = value;
this.save();
}
/** The settings, the offset a program set the clock to, any clock registers held as written, and the bus. */
snapshotState() {
const { store, timeOffset, heldDate, heldTime, enabled, isRead, addressSelect, dataSelect, cmosAddr } = this;
return {
store: [...store],
timeOffset,
heldDate: heldDate && { ...heldDate },
heldTime: { ...heldTime },
enabled,
isRead,
addressSelect,
dataSelect,
cmosAddr,
};
}
/** Keeps nothing restored; a state saved with only the bus leaves the settings and clock as they are. */
restoreState(state) {
const { enabled, isRead, addressSelect, dataSelect, cmosAddr } = state;
if (state.store) {
const store = fullStore(state.store);
const { timeOffset, heldDate, heldTime } = state;
Object.assign(this, {
store,
timeOffset,
heldDate: heldDate && { ...heldDate },
heldTime: { ...heldTime },
});
}
Object.assign(this, { enabled, isRead, addressSelect, dataSelect, cmosAddr });
}
/**
* Joins a shared session, whose snapshot then brings in the host's chip: until the session is left
* nothing is stored, and the clock reads `now`, the session's wall time in milliseconds.
*/
joinSession(now) {
if (!this.beforeSession) {
const { persistence, store, utc, timeOffset, heldDate, heldTime } = this;
this.beforeSession = { persistence, store, now: this.now, utc, timeOffset, heldDate, heldTime };
}
this.store = [...this.store];
this.heldTime = { ...this.heldTime };
this.persistence = null;
this.now = now;
this.utc = true;
}
/** Back to this machine's own settings and clock, as they were before the session. */
leaveSession() {
if (!this.beforeSession) return;
Object.assign(this, this.beforeSession);
this.beforeSession = null;
}
// Whole seconds, all the clock keeps, so that a replay is handed the second each read saw.
clockMs() {
const ms = Math.floor(this.now() / 1000) * 1000;
return this.inputLog ? this.inputLog.sample("rtc", ms) : ms;
}
bbcDateTime() {
const result = new Date(this.clockMs() + this.timeOffset);
result.setMilliseconds(0);
return this.utc ? utcView(result) : result;
}
calendarRegisters(current) {
return (
this.heldDate ?? {
day: toBcd(current.getDate()),
month: toBcd(current.getMonth() + 1),
year: toBcd(current.getFullYear() % 100),
}
);
}
setTimeFrom(bbcTime) {
this.timeOffset = bbcTime.getTime() - this.clockMs();
}
writeTime(register, value) {
const { limit, set } = TimeRegisters[register];
if (!isBcdBelow(value, limit)) {
this.heldTime[register] = value;
return;
}
delete this.heldTime[register];
const bbcTime = this.bbcDateTime();
set(bbcTime, fromBcd(value));
this.setTimeFrom(bbcTime);
}
writeCalendar(field, value) {
const bbcTime = this.bbcDateTime();
const registers = { ...this.calendarRegisters(bbcTime), [field]: value };
const { day, month, year } = registers;
bbcTime.setFullYear(MosCentury + fromBcd(year), fromBcd(month) - 1, fromBcd(day));
const isRealDay =
toBcd(bbcTime.getDate()) === day &&
toBcd(bbcTime.getMonth() + 1) === month &&
toBcd(bbcTime.getFullYear() % 100) === year;
if (isRealDay) {
this.heldDate = null;
this.setTimeFrom(bbcTime);
} else {
this.heldDate = registers;
}
}
read() {
if (!this.enabled) return 0xff;
// To drive the bus we need:
// - CMOS enabled.
// - Address Select low.
// - Data Select high.
// - Read high.
if (!this.addressSelect && this.dataSelect && this.isRead) {
// The first 10 bytes of CMOS RAM store the RTC clock
if (this.cmosAddr < 10) {
const current = this.bbcDateTime();
switch (this.cmosAddr) {
case 0:
case 2:
case 4:
return this.heldTime[this.cmosAddr] ?? toBcd(TimeRegisters[this.cmosAddr].get(current));
case 6:
return toBcd(current.getDay() + 1);
case 7:
return this.calendarRegisters(current).day;
case 8:
return this.calendarRegisters(current).month;
case 9:
return this.calendarRegisters(current).year;
}
} else {
return this.store[this.cmosAddr] & 0xff;
}
}
return 0xff;
}
/** Takes up the select and read lines as port B and IC32 drive them, making no access. */
followLines(portBpins, IC32) {
this.enabled = !!(portBpins & 0x40);
if (!this.enabled) return;
this.isRead = !!(IC32 & 2);
this.dataSelect = !!(IC32 & 4);
this.addressSelect = !!(portBpins & 0x80);
}
writeControl(portBpins, portApins, IC32) {
const { dataSelect: oldDataSelect, addressSelect: oldAddressSelect } = this;
this.followLines(portBpins, IC32);
if (!this.enabled) return;
if (oldAddressSelect && !this.addressSelect) this.cmosAddr = portApins & 0x3f;
if (oldDataSelect && !this.dataSelect && !this.addressSelect && !this.isRead) {
if (this.cmosAddr > 0xb) {
this.store[this.cmosAddr] = portApins;
this.keep(this.cmosAddr, portApins);
} else {
switch (this.cmosAddr) {
case 0:
case 2:
case 4:
this.writeTime(this.cmosAddr, portApins);
break;
case 7:
this.writeCalendar("day", portApins);
break;
case 8:
this.writeCalendar("month", portApins);
break;
case 9:
this.writeCalendar("year", portApins);
break;
}
}
}
}
}
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