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import { WithKeyMatrix } from "./keymap.js";
// 8255 Programmable Peripheral Interface Adapter for the Acorn Atom.
// Reference: http://mdfs.net/Docs/Comp/Acorn/Atom/atap25.htm
// Memory map: http://mdfs.net/Docs/Comp/Acorn/Atom/MemoryMap
//
// Port A - 0xB000 (output)
// bits 0-3: Keyboard row select
// bits 4-7: MC6847 graphics mode
//
// Port B - 0xB001 (input)
// bits 0-5: Keyboard column (active low)
// bit 6: CTRL key (low when pressed)
// bit 7: SHIFT key (low when pressed)
//
// Port C - 0xB002 (mixed I/O)
// Output bits:
// 0: Tape output
// 1: Enable 2.4 kHz to cassette output
// 2: Loudspeaker
// 3: Colour Set Select (CSS)
// Input bits:
// 4: 2.4 kHz input
// 5: Cassette input
// 6: REPT key (low when pressed)
// 7: 60 Hz VSync signal (low during flyback)
//
// Keyboard matrix (active low, active when key pressed):
// Port A row → 9 8 7 6 5 4 3 2 1 0
// Port B col ↓
// ~b0 : SPC [ \ ] ^ LCK <-> ^-v
// ~b1 : ENT CPY DEL 0 1 2 3
// ~b2 : 4 5 6 7 8 9 : ; < =
// ~b3 : > ? @ A B C D E F G
// ~b4 : H I J K L M N O P Q
// ~b5 : R S T U V W X Y Z ESC
// ~b6 : Ctrl
// ~b7 : Shift
const PORTA = 0x0,
PORTB = 0x1,
PORTC = 0x2,
CREG = 0x3; // control register
class PPIA {
constructor(cpu) {
this.cpu = cpu;
this.latcha = 0;
this.latchc = 0;
this.portapins = 0;
this.portbpins = 0;
this.portcpins = 0;
this.creg = 0;
this.speaker = 0;
}
reset() {
//http://members.casema.nl/hhaydn/8255_pin.html
this.latcha = this.latchc = 0x00;
}
setVBlankInt(level) {
// level == 1 when in the vsync
// FE66_wait_for_flyback_start will loop until bit 7 (copied into N register using BIT)
// of B002 is not 0 (i.e until BPL fails when bit 7 is 1)
// then
// FE6B_wait_for_flyback will loop until bit 7 of B002 is (copied into N register using BIT)
// of B002 is not 1 (i.e until BMI fails when bit 7 is 0)
//60 Hz sync signal - normally 1 during the frame, but goes 0 at start of flyback (at the end of a frame).
//opposite of the 'level'
if (!level) {
// set bit 7 to 1 - in frame
this.latchc |= 0x80;
} else {
// set bit 7 to 0 - in vsync
this.latchc &= ~0x80;
}
this.recalculatePortCPins();
}
/*
Port C - #B002
Output bits: Function:
0 Tape output
1 Enable 2.4 kHz to cassette output
2 Loudspeaker
3 Not used
Input bits: Function:
4 2.4 kHz input
5 Cassette input
6 REPT key (low when pressed)
7 60 Hz sync signal (low during flyback)
The port C output lines, bits 0 to 3, may be used for user applications when the cassette interface is not being used.
*/
write(addr, val) {
val |= 0;
// The 8255 only decodes A0-A1; addresses 4-7 mirror 0-3.
// Addresses 8-15 are outside the 8255's decode range.
if ((addr & 0xf) >= 0x8) return;
switch (addr & 0x3) {
case PORTA:
this.latcha = val;
this.recalculatePortAPins();
break;
case PORTB:
// Port B is input-only; writes are ignored.
break;
case PORTC:
this.latchc = (this.latchc & 0xf0) | (val & 0x0f);
this.recalculatePortCPins();
break;
case CREG: {
this.creg = val & 0xff;
// 8255 CREG: D7=1 is mode-set, ignored, as port directions are fixed at what the Atom ROM's
// reset selects (#1436).
// D7=0 is Bit Set/Reset (BSR) for individual port C output bits.
if (val & 0x80) break;
// BSR: set or clear a single port C output bit.
// NOTE: Simplified: only handles bits 2 (speaker) and 3 (CSS),
// and rebuilds the lower nibble. Works because the Atom ROM
// only BSR-toggles these two bits.
let speaker = this.latchc & 0x04;
let css = this.latchc & 0x08;
switch (val & 0xe) {
case 0x4: // port C pin 2 (speaker)
speaker = (val & 1) << 2;
break;
case 0x6: // port C pin 3 (CSS)
css = (val & 1) << 3;
break;
}
this.latchc = (this.latchc & 0xf0) | css | speaker;
this.recalculatePortCPins();
break;
}
}
}
read(addr) {
if ((addr & 0xf) >= 0x8) return addr >>> 8; // open bus
switch (addr & 0x3) {
case PORTA:
this.recalculatePortAPins();
return this.portapins;
case PORTB: {
const keyrow = this.portapins & 0x0f;
const n = this.keys[keyrow];
let r = 0xff; // all keys unpressed
for (let b = 0; b <= 9; b++) r &= ~(n[b] << b);
// CTRL and SHIFT are always readable regardless of row selection
const ctrl_shift = (this.keys[0][7] << 7) | (this.keys[0][6] << 6);
r &= ~(ctrl_shift & 0xc0);
return r;
}
case PORTC: {
this.recalculatePortCPins();
// Force HZIN (bit 4) high
this.portcpins = (this.portcpins & 0xef) | (1 << 4);
// Read back full port C state: output bits 0-3 from latch,
// input bits 4-7 from pins, with REPT key overlay on bit 6.
let val = this.portcpins;
// REPT key: bit 6 is LOW when pressed
const rept_key = (!this.keys[1][6] << 6) & 0x40;
val = (val & ~0x40) | rept_key;
// Track cassette input transitions. The Atom ROM tape routines:
// 0xfc0a - OSBGET: get byte from tape (every 3.34ms)
// 0xfcd2 - test tape input pulse (every 0.033ms / 33 cycles)
// 0xfcc2 - count duration of tape pulse (<8 loops = '1', >=8 = '0')
// 0xfe6e, 0xfe9d, 0xfe69 - flyback/VSync routines
// Between each receiveBit, fcd2 is called ~6 times (33 cycles each).
return val;
}
default:
return addr >>> 8; // CREG and unmapped registers return open bus
}
}
recalculatePortAPins() {
this.portapins = this.latcha;
this.drivePortA();
this.portAUpdated();
}
recalculatePortCPins() {
this.portcpins = this.latchc;
this.drivePortC();
this.portCUpdated();
}
// No-op hooks for subclass override
drivePortA() {}
drivePortC() {}
portAUpdated() {}
portCUpdated() {}
}
const AtomKeyColumns = 10;
// On the atom, the PPIA does the keyboard, speaker and tape.
// On the BBC, sysVIA does the keyboard and pokes the soundchip
// and the ACIA does the tape
export class AtomPPIA extends WithKeyMatrix(PPIA) {
constructor(cpu, initialLayout, scheduler) {
super(cpu);
this._initKeyMatrix(ATOM.SHIFT, AtomKeyColumns);
this.setKeyLayout(initialLayout);
// The Atom has no lock lights. Report caps lock as "on" and shift
// lock as "off" so the paste routine's lock-toggle logic is never
// triggered (it toggles CAPSLOCK when !capsLockLight, and SHIFTLOCK
// when shiftLockLight).
this.capsLockLight = true;
this.shiftLockLight = false;
this.motorOn = false;
this.reset();
this.runTapeTask = scheduler.newTask(() => this.runTape());
}
reset() {
super.reset();
this.lastSpeakerBit = (this.latchc & 0x04) >>> 2;
}
setKeyLayout(map) {
this.keycodeToRowCol = getKeyMapAtom(map);
}
// nothing on ATOM
updateKeys() {}
// nothing on ATOM
polltime() {}
portAUpdated() {
this.updateKeys();
}
portCUpdated() {
const speakerBit = (this.portcpins & 0x04) >>> 2;
if (speakerBit !== this.lastSpeakerBit) {
this.lastSpeakerBit = speakerBit;
this.cpu.soundChip.speakerGenerator.pushBit(speakerBit, this.cpu.currentCycles, this.cpu.cycleSeconds);
}
}
drivePortA() {
this.updateKeys();
}
drivePortC() {
// Nothing driving here.
}
// ATOM TAPE SUPPORT
// from ACIA on BBC
// set by TAPE
tone(freq) {
let toneGen = this.cpu.soundChip.toneGenerator;
if (!freq) toneGen.mute();
else toneGen.tone(freq);
}
// The Atom has no carrier detect.
setTapeCarrier() {}
// Receive bits from tape (called by tape.poll via PPIA, not ACIA like BBC).
// Called once every ~208 clock cycles (208us at 1 MHz).
// Recognition: '1' = 4 half-cycles at 1.2 kHz (duration < 8),
// '0' = 8 half-cycles at 2.4 kHz (duration >= 8).
// Leader tone is a stream of '1' bits.
receiveBit(bit) {
bit |= 0;
this.latchc = (this.latchc & 0xdf) | (bit << 5);
this.recalculatePortCPins();
}
// nothing on ATOM
receive(/*_byte*/) {}
/** A tape put in starts stopped, whatever the last one was doing. */
setTape(tape) {
this.stopTape();
this.tape = tape;
}
rewindTape() {
this.stopTape();
Eif (this.tape) this.tape.rewind();
}
/** On the Atom the recorder's PLAY is the motor: there is no relay for it to work against. */
get playPressed() {
return this.motorOn;
}
get tapeRunning() {
return this.motorOn;
}
pressPlay() {
this.playTape();
}
pressStop() {
this.stopTape();
}
playTape() {
Eif (this.tape) {
this.refuseReplaysIfMotorChanges(true);
this.motorOn = true;
this.runTape();
}
}
stopTape() {
this.refuseReplaysIfMotorChanges(false);
this.motorOn = false;
if (this.tape) {
const toneGen = this.cpu.soundChip.toneGenerator;
toneGen.mute();
this.runTapeTask.cancel();
}
}
// The tape is not in a snapshot, and a replay would read on from where it is now.
refuseReplaysIfMotorChanges(on) {
if (on !== this.motorOn) this.inputLog?.refuse("the cassette motor starting or stopping");
}
/** Polls the tape and books the next poll; the Atom's PLAY is its motor, so a tape that runs out stops. */
runTape() {
Iif (!this.tape) return;
const delay = this.tape.poll(this);
if (delay === undefined) this.stopTape();
else this.runTapeTask.reschedule(delay);
}
updateIrq() {}
snapshotState() {
return {
latcha: this.latcha,
latchc: this.latchc,
portapins: this.portapins,
portbpins: this.portbpins,
portcpins: this.portcpins,
creg: this.creg,
keys: this.keys.map((row) => Array.from(row)),
lastSpeakerBit: this.lastSpeakerBit,
};
}
restoreState(state) {
this.latcha = state.latcha;
this.latchc = state.latchc;
this.portapins = state.portapins;
this.portbpins = state.portbpins;
this.portcpins = state.portcpins;
this.creg = state.creg;
Eif (state.keys) {
for (let i = 0; i < state.keys.length; i++) {
this.keys[i].set(state.keys[i]);
}
}
this.lastSpeakerBit = state.lastSpeakerBit;
// Which held key was forcing shift is not saved, so the matrix's shift is taken as the shift key's.
const [shiftCol, shiftRow] = ATOM.SHIFT;
this.shift.restore({ physicalShiftDown: !!this.keys[shiftCol][shiftRow], shiftOverrideActive: false });
}
}
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