Press n or j to go to the next uncovered block, b, p or k for the previous block.
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const IerReadsSet = 0x80;
const ControlLineModes = [
"falling edge",
"falling edge, independent",
"rising edge",
"rising edge, independent",
"handshake output",
"pulse output",
"low output",
"high output",
];
const Timer1Modes = ["one-shot", "continuous", "one-shot, PB7 pulse", "continuous, PB7 square wave"];
const ShiftRegisterModes = [
"off",
"in by T2",
"in by clock",
"in by CB1",
"out free-running by T2",
"out by T2",
"out by clock",
"out by CB1",
];
const Timer1Forms = Timer1Modes.map((mode) => `T1 ${mode}`);
const Timer2Modes = ["T2 counts PB6 pulses", "T2 one-shot"];
const ShiftRegisterForms = ShiftRegisterModes.map((mode) => `SR ${mode}`);
const CountForms = ["65535 cycles", "65535 pulses"];
/**
* @typedef {object} ControlLine what a VIA's control line is wired to on this machine
* @property {string} name CA1, CA2, CB1 or CB2
* @property {string} wiring a word or two, shown beside the name
* @property {string} title what it is wired to, in full
*/
/**
* @typedef {object} ViaWiring
* @property {ControlLine} ca1
* @property {ControlLine} ca2
* @property {ControlLine} cb1
* @property {ControlLine} cb2
* @property {string} t1 what timer 1 reaching zero means here
*/
/**
* @typedef {object} PortLines what a port's lines are wired to
* @property {string} title
* @property {(pins: number, state: object) => import("./decoded-registers.js").Meaning[]} decode
*/
/**
* The registers every VIA has, as the decoded panels show them. Reading changes nothing the machine sees: the timers
* are caught up as {@link Via#peekTimers} does, which is also what brings the interrupt flags up to date.
* @param {import("../via.js").Via} via
*/
export function viaState(via) {
const { t1c, t1l, t2c, t2l } = via.peekTimers();
return {
ora: via.ora,
ddra: via.ddra,
portA: via.portapins,
orb: via.orb,
ddrb: via.ddrb,
portB: via.portbpins,
pcr: via.pcr,
acr: via.acr,
ifr: via.ifr,
ier: via.ier | IerReadsSet,
t1c,
t1l,
t2c,
t2l,
};
}
function controlLineForms(line) {
return ControlLineModes.map((mode) => `${line.name} ${line.wiring}: ${mode}`);
}
function edgeLine(line, risingBit) {
const edge = risingBit ? "rising edge" : "falling edge";
return spelt(
`${line.name} ${line.wiring}: ${edge}`,
`${line.name}, ${line.title}: interrupts on a ${edge}`,
controlLineForms(line),
);
}
function controlLine(line, mode) {
const what = ControlLineModes[mode];
return spelt(
`${line.name} ${line.wiring}: ${what}`,
`${line.name}, ${line.title}: ${what}`,
controlLineForms(line),
);
}
function decodePcr(pcr, { ca1, ca2, cb1, cb2 }) {
return [
edgeLine(ca1, pcr & 1),
controlLine(ca2, (pcr >>> 1) & 7),
edgeLine(cb1, pcr & 0x10),
controlLine(cb2, (pcr >>> 5) & 7),
];
}
function decodeAcr(acr) {
return [
spelt(Timer1Forms[acr >>> 6], "Bits 6 and 7: timer 1's mode", Timer1Forms),
spelt(Timer2Modes[acr & 0x20 ? 0 : 1], "Bit 5: timer 2's mode", Timer2Modes),
spelt(ShiftRegisterForms[(acr >>> 2) & 7], "Bits 2 to 4: the shift register's mode", ShiftRegisterForms),
lit("PB latch", "Bit 1: port B latches its input on CB1's active edge", acr & 2),
lit("PA latch", "Bit 0: port A latches its input on CA1's active edge", acr & 1),
];
}
function inCycles(value) {
return [spelt(`${value} cycles`, "In cycles: the VIA counts at 1 MHz", CountForms)];
}
function decodeT2Counter(value, { acr }) {
if (acr & 0x20) return [spelt(`${value} pulses`, "Falling edges on PB6 still to count", CountForms)];
return inCycles(value);
}
/** By bit number in the IFR and IER. */
function interruptSources({ ca1, ca2, cb1, cb2, t1 }) {
const line = ({ name, wiring, title }) => ({ name: `${name} ${wiring}`, title: `${name}: ${title}` });
return [
line(ca2),
line(ca1),
{ name: "SR", title: "The shift register has shifted eight bits" },
line(cb2),
line(cb1),
{ name: "T2", title: "Timer 2 has reached zero" },
{ name: "T1", title: t1 },
];
}
/**
* The output registers, data directions and lines of both ports.
* @param {{a: PortLines, b: PortLines}} ports
*/
export function portsSection({ a, b }) {
return {
heading: "Ports",
registers: [
register("ORA", "Output register A", 8, (s) => s.ora, noMeaning),
register("DDRA", "Port A's data direction: a set bit drives its line", 8, (s) => s.ddra, noMeaning),
register("PA", a.title, 8, (s) => s.portA, a.decode),
register("ORB", "Output register B", 8, (s) => s.orb, noMeaning),
register("DDRB", "Port B's data direction: a set bit drives its line", 8, (s) => s.ddrb, noMeaning),
register("PB", b.title, 8, (s) => s.portB, b.decode),
],
};
}
/**
* The PCR and ACR, and the interrupts flagged and enabled, named by what this machine wires to them.
* @param {ViaWiring} wiring
*/
export function controlSection(wiring) {
const sources = interruptSources(wiring);
return {
heading: "Control",
registers: [
register(
"PCR",
"Peripheral control: CA1, CA2, CB1 and CB2",
8,
(s) => s.pcr,
(pcr) => decodePcr(pcr, wiring),
),
register("ACR", "Auxiliary control: the timers, shift register and latches", 8, (s) => s.acr, decodeAcr),
register(
"IFR",
"Interrupt flags",
8,
(s) => s.ifr,
namedBits([...sources, { name: "IRQ", title: "Some enabled flag is set" }]),
),
register("IER", "Interrupts enabled", 8, (s) => s.ier, namedBits(sources)),
],
};
}
export const TimersSection = {
heading: "Timers",
registers: [
register("T1C", "Timer 1's counter, as a program reads it", 16, (s) => s.t1c, inCycles),
register("T1L", "Timer 1's latch", 16, (s) => s.t1l, inCycles),
register("T2C", "Timer 2's counter, as a program reads it", 16, (s) => s.t2c, decodeT2Counter),
register("T2L", "Timer 2's latch, as last written", 16, (s) => s.t2l, inCycles),
],
};
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