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Tweaks to how flags work
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@mattgodbolt
mattgodbolt committed Dec 24, 2023
1 parent 18e8ebb commit faacef7
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Showing 2 changed files with 106 additions and 44 deletions.
86 changes: 74 additions & 12 deletions 6502.js
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Original file line number Diff line number Diff line change
Expand Up @@ -16,49 +16,64 @@ const signExtend = utils.signExtend;
function _set(byte, mask, set) {
return (byte & ~mask) | (set ? mask : 0);
}

class Flags {
constructor() {
this._byte = 0x30;
}

get c() {
return !!(this._byte & 0x01);
}

set c(val) {
this._byte = _set(this._byte, 0x01, val);
}

get z() {
return !!(this._byte & 0x02);
}

set z(val) {
this._byte = _set(this._byte, 0x02, val);
}

get i() {
return !!(this._byte & 0x04);
}

set i(val) {
this._byte = _set(this._byte, 0x04, val);
}

get d() {
return !!(this._byte & 0x08);
}

set d(val) {
this._byte = _set(this._byte, 0x08, val);
}

get v() {
return !!(this._byte & 0x40);
}

set v(val) {
this._byte = _set(this._byte, 0x40, val);
}

get n() {
return !!(this._byte & 0x80);
}

set n(val) {
this._byte = _set(this._byte, 0x80, val);
}

reset() {
this._byte = 0x30;
}

debugString() {
return (
(this.n ? "N" : "n") +
Expand All @@ -70,9 +85,17 @@ class Flags {
(this.c ? "C" : "c")
);
}

setzn(v) {
v &= 0xff;
this._byte = (this._byte & ~(0x02 | 0x80)) | (v & 0x80) | (v === 0 ? 0x02 : 0x00);
return v | 0;
}

asByte() {
return this._byte | 0x30;
}

setFromByte(byte) {
this._byte = byte | 0x30;
}
Expand All @@ -82,11 +105,13 @@ class Base6502 {
constructor(model) {
this.model = model;
this.a = this.x = this.y = this.s = 0;
this.p = new Flags();
this.pc = 0;
this.opcodes = model.nmos ? opcodes.Cpu6502(this) : opcodes.Cpu65c12(this);
this.disassembler = this.opcodes.disassembler;
this.forceTracing = false;
this.runner = this.opcodes.runInstruction;
this.interrupt = 0;

if (model.nmos) {
this.adc = function (addend) {
Expand Down Expand Up @@ -147,10 +172,25 @@ class Base6502 {
}

setzn(v) {
v &= 0xff;
this.p.z = !v;
this.p.n = !!(v & 0x80);
return v | 0;
return this.p.setzn(v);
}

// eslint-disable-next-line no-unused-vars
writemem(address, value) {
throw new Error("Must be overridden");
}

writememZpStack(address, value) {
this.writemem(address, value);
}

// eslint-disable-next-line no-unused-vars
readmem(address) {
throw new Error("Must be overridden");
}

readmemZpStack(address) {
return this.readmem(address);
}

push(v) {
Expand All @@ -167,6 +207,10 @@ class Base6502 {
this.nmi = !!nmi;
}

polltime() {
throw new Error("Must be overridden");
}

brk(isIrq) {
// Behavior here generally discovered via Visual 6502 analysis.
// 6502 has a quirky BRK; it was sanitized in 65c12.
Expand Down Expand Up @@ -245,8 +289,7 @@ class Base6502 {
const result = this.a + addend + (this.p.c ? 1 : 0);
this.p.v = !!((this.a ^ result) & (addend ^ result) & 0x80);
this.p.c = !!(result & 0x100);
this.a = result & 0xff;
this.setzn(this.a);
this.a = this.p.setzn(result);
}

// For flags and stuff see URLs like:
Expand Down Expand Up @@ -310,7 +353,7 @@ class Base6502 {
ah = (ah - 10) & 0xf;
this.p.c = true;
}
this.a = this.setzn(al | (ah << 4));
this.a = this.p.setzn(al | (ah << 4));
}

sbcBCDcmos(subend) {
Expand All @@ -324,7 +367,7 @@ class Base6502 {
if (al < 0) result -= 0x06;

this.adcNonBCD(subend ^ 0xff); // For flags
this.a = this.setzn(result);
this.a = this.p.setzn(result);
}

arr(arg) {
Expand All @@ -351,7 +394,7 @@ class Base6502 {
this.p.v = !!(((this.a >>> 7) ^ (this.a >>> 6)) & 0x01);
this.a >>>= 1;
if (this.p.c) this.a |= 0x80;
this.setzn(this.a);
this.p.setzn(this.a);
this.p.c = !!(this.a & 0x40);
}
}
Expand All @@ -365,16 +408,17 @@ class Tube6502 extends Base6502 {
this.romPaged = true;
this.memory = new Uint8Array(65536);
this.rom = new Uint8Array(4096);
this.p = new Flags();

this.tube = new Tube(cpu, this);
}

reset(hard) {
this.romPaged = true;
this.pc = this.readmem(0xfffc) | (this.readmem(0xfffd) << 8);
this.p.i = true;
this.tube.reset(hard);
}

readmem(offset) {
if ((offset & 0xfff8) === 0xfef8) {
if ((offset & 7) === 0) {
Expand All @@ -387,30 +431,38 @@ class Tube6502 extends Base6502 {
}
return this.memory[offset & 0xffff];
}

readmemZpStack(offset) {
return this.memory[offset & 0xffff];
}

writemem(addr, b) {
if ((addr & 0xfff8) === 0xfef8) {
return this.tube.parasiteWrite(addr, b);
}
this.memory[addr & 0xffff] = b;
}

writememZpStack(addr, b) {
this.memory[addr & 0xffff] = b;
}

polltime(cycles) {
this.cycles -= cycles;
}

polltimeAddr(cycles) {
this.polltime(cycles);
}

read(addr) {
return this.tube.hostRead(addr);
}

write(addr, b) {
this.tube.hostWrite(addr, b);
}

execute(cycles) {
this.cycles += cycles * 2;
if (this.cycles < 3) return;
Expand All @@ -421,6 +473,7 @@ class Tube6502 extends Base6502 {
if (this.takeInt) this.brk(true);
}
}

async loadOs() {
console.log("Loading tube rom from roms/" + this.model.os);
const tubeRom = this.rom;
Expand All @@ -437,13 +490,17 @@ class FakeTube {
read() {
return 0xfe;
}

write() {}

execute() {}

reset() {}
}

class FakeUserPort {
write() {}

read() {
return 0xff;
}
Expand All @@ -465,6 +522,7 @@ class DebugHook {
this.functionName = functionName;
this.handlers = [];
}

add(handler) {
const self = this;
this.handlers.push(handler);
Expand All @@ -485,6 +543,7 @@ class DebugHook {
};
return handler;
}

remove(handler) {
const i = this.handlers.indexOf(handler);
if (i < 0) throw "Unable to find debug hook handler";
Expand All @@ -493,6 +552,7 @@ class DebugHook {
this.cpu[this.functionName] = null;
}
}

clear() {
this.handlers = [];
this.cpu[this.functionName] = null;
Expand All @@ -519,7 +579,6 @@ export class Cpu6502 extends Base6502 {
this.osOffset = this.romOffset + 16 * 16 * 1024;
this.romsel = 0;
this.acccon = 0;
this.interrupt = 0;
this.FEslowdown = [true, false, true, true, false, false, true, false];
this.oldPcArray = new Uint16Array(256);
this.oldAArray = new Uint8Array(256);
Expand Down Expand Up @@ -624,6 +683,7 @@ export class Cpu6502 extends Base6502 {
if (this._debugRead) this._debugRead(addr, 0, res);
return res | 0;
}

writememZpStack(addr, b) {
addr &= 0xffff;
b |= 0;
Expand Down Expand Up @@ -873,6 +933,7 @@ export class Cpu6502 extends Base6502 {
if (addr < 0xfc00 || addr >= 0xff00) return;
this.writeDevice(addr, b);
}

writeDevice(addr, b) {
b |= 0;

Expand Down Expand Up @@ -1135,7 +1196,6 @@ export class Cpu6502 extends Base6502 {
this.cycleSeconds = 0;
}
this.pc = this.readmem(0xfffc) | (this.readmem(0xfffd) << 8);
this.p = new Flags();
this.p.i = true;
this.nmi = false;
this.halted = false;
Expand Down Expand Up @@ -1232,6 +1292,7 @@ export class Cpu6502 extends Base6502 {
return this.executeInternalFast();
}
}

executeInternal() {
let first = true;
while (!this.halted && this.currentCycles < this.targetCycles) {
Expand All @@ -1253,6 +1314,7 @@ export class Cpu6502 extends Base6502 {
}
return !this.halted;
}

executeInternalFast() {
while (!this.halted && this.currentCycles < this.targetCycles) {
this.memStatOffset = this.memStatOffsetByIFetchBank[this.pc >>> 12];
Expand Down
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