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Refactor page computations

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Will Scullin 2021-10-09 21:23:15 -07:00
parent b1e318511f
commit 5c1be13537
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GPG Key ID: 26DCD1042C6638CD
1 changed files with 70 additions and 90 deletions
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160
js/cpu6502.ts
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@ -326,14 +326,6 @@ export default class CPU6502 {
this.cycles++;
}
private workCycle(addr: word, val: byte) {
if (this.is65C02) {
this.readByte(addr);
} else {
this.writeByte(addr, val);
}
}
private readWord(addr: word): word {
return this.readByte(addr) | (this.readByte(addr + 1) << 8);
}
@ -371,6 +363,40 @@ export default class CPU6502 {
return (msb << 8) | lsb;
}
// Helpers that replicate false reads and writes during work cycles that
// vary between CPU versions
private workCycle(addr: word, val: byte) {
if (this.is65C02) {
this.readByte(addr);
} else {
this.writeByte(addr, val);
}
}
private writePageCross(pc: word, addr: word, addrIdx: word): void {
const oldPage = addr & 0xff00;
if (this.is65C02) {
this.readByte(pc);
} else {
const off = addrIdx & 0xff;
this.readByte(oldPage | off);
}
}
private readPageCross(pc: word, addr: word, addrIdx: word): void {
const oldPage = addr & 0xff00;
const newPage = addrIdx & 0xff00;
if (newPage !== oldPage) {
if (this.is65C02) {
this.readByte(pc);
} else {
const off = addrIdx & 0xff;
this.readByte(oldPage | off);
}
}
}
/*
* Implied function
*/
@ -400,38 +426,20 @@ export default class CPU6502 {
// $0000,X
readAbsoluteX = (): byte => {
let addr = this.readWordPC();
const addr = this.readWordPC();
const pc = this.addr;
const oldPage = addr >> 8;
addr = (addr + this.xr) & 0xffff;
const newPage = addr >> 8;
if (newPage != oldPage) {
const off = addr & 0xff;
if (this.is65C02) {
this.readByte(pc);
} else {
this.readByte(oldPage << 8 | off);
}
}
return this.readByte(addr);
const addrIdx = (addr + this.xr) & 0xffff;
this.readPageCross(pc, addr, addrIdx);
return this.readByte(addrIdx);
}
// $0000,Y
readAbsoluteY = (): byte => {
let addr = this.readWordPC();
const addr = this.readWordPC();
const pc = this.addr;
const oldPage = addr >> 8;
addr = (addr + this.yr) & 0xffff;
const newPage = addr >> 8;
if (newPage != oldPage) {
const off = addr & 0xff;
if (this.is65C02) {
this.readByte(pc);
} else {
this.readByte(oldPage << 8 | off);
}
}
return this.readByte(addr);
const addrIdx = (addr + this.yr) & 0xffff;
this.readPageCross(pc, addr, addrIdx);
return this.readByte(addrIdx);
}
// $00,X
@ -459,26 +467,16 @@ export default class CPU6502 {
// ($00),Y
readZeroPageIndirectY = (): byte => {
const zpAddr = this.readBytePC();
const oldPC = this.addr;
let addr = this.readZPWord(zpAddr);
const oldPage = addr >> 8;
addr = (addr + this.yr) & 0xffff;
const newPage = addr >> 8;
if (newPage != oldPage) {
const off = addr & 0xff;
if (this.is65C02) {
this.readByte(oldPC);
} else {
this.readByte(oldPage << 8 | off);
}
}
return this.readByte(addr);
const pc = this.addr;
const addr = this.readZPWord(zpAddr);
const addrIdx = (addr + this.yr) & 0xffff;
this.readPageCross(pc, addr, addrIdx);
return this.readByte(addrIdx);
}
// ($00) (65C02)
readZeroPageIndirect = (): byte => {
const addr = this.readZPWord(this.readBytePC());
return this.readByte(addr);
return this.readByte(this.readZPWord(this.readBytePC()));
}
/*
@ -497,32 +495,20 @@ export default class CPU6502 {
// $0000,X
writeAbsoluteX = (val: byte) => {
let addr = this.readWordPC();
const addr = this.readWordPC();
const pc = this.addr;
const oldPage = addr >> 8;
addr = (addr + this.xr) & 0xffff;
const off = addr & 0xff;
if (this.is65C02) {
this.readByte(pc);
} else {
this.readByte(oldPage << 8 | off);
}
this.writeByte(addr, val);
const addrIdx = (addr + this.xr) & 0xffff;
this.writePageCross(pc, addr, addrIdx);
this.writeByte(addrIdx, val);
}
// $0000,Y
writeAbsoluteY = (val: byte) => {
let addr = this.readWordPC();
const addr = this.readWordPC();
const pc = this.addr;
const oldPage = addr >> 8;
addr = (addr + this.yr) & 0xffff;
const off = addr & 0xff;
if (this.is65C02) {
this.readByte(pc);
} else {
this.readByte(oldPage << 8 | off);
}
this.writeByte(addr, val);
const addrIdx = (addr + this.yr) & 0xffff;
this.writePageCross(pc, addr, addrIdx);
this.writeByte(addrIdx, val);
}
// $00,X
@ -551,16 +537,10 @@ export default class CPU6502 {
writeZeroPageIndirectY = (val: byte) => {
const zpAddr = this.readBytePC();
const pc = this.addr;
let addr = this.readZPWord(zpAddr);
const oldPage = addr >> 8;
addr = (addr + this.yr) & 0xffff;
const off = addr & 0xff;
if (this.is65C02) {
this.readByte(pc);
} else {
this.readByte(oldPage << 8 | off);
}
this.writeByte(addr, val);
const addr = this.readZPWord(zpAddr);
const addrIdx = (addr + this.yr) & 0xffff;
this.writePageCross(pc, addr, addrIdx);
this.writeByte(addrIdx, val);
}
// ($00) (65C02)
@ -919,12 +899,12 @@ export default class CPU6502 {
const off = this.readBytePC(); // changes pc
if ((f & this.sr) !== 0) {
this.readByte(this.pc);
const oldPage = this.pc >> 8;
const oldPage = this.pc & 0xff00;
this.pc += off > 127 ? off - 256 : off;
this.pc &= 0xffff;
const newPage = this.pc >> 8;
const newPage = this.pc & 0xff00;
const newOff = this.pc & 0xff;
if (newPage != oldPage) this.readByte(oldPage << 8 | newOff);
if (newPage !== oldPage) this.readByte(oldPage | newOff);
}
}
@ -932,12 +912,12 @@ export default class CPU6502 {
const off = this.readBytePC(); // changes pc
if ((f & this.sr) === 0) {
this.readByte(this.pc);
const oldPage = this.pc >> 8;
const oldPage = this.pc & 0xff00;
this.pc += off > 127 ? off - 256 : off;
this.pc &= 0xffff;
const newPage = this.pc >> 8;
const newPage = this.pc & 0xff00;
const newOff = this.pc & 0xff;
if (newPage != oldPage) this.readByte(oldPage << 8 | newOff);
if (newPage !== oldPage) this.readByte(oldPage | newOff);
}
}
@ -949,12 +929,12 @@ export default class CPU6502 {
this.writeByte(zpAddr, val);
const off = this.readBytePC(); // changes pc
const oldPc = this.pc;
const oldPage = oldPc >> 8;
const oldPage = oldPc & 0xff00;
let newPC = this.pc + (off > 127 ? off - 256 : off);
newPC &= 0xffff;
const newOff = newPC & 0xff;
this.readByte((oldPage << 8) | newOff);
this.readByte(oldPage | newOff);
if (((1 << b) & val) === 0) {
this.pc = newPC;
}
@ -966,12 +946,12 @@ export default class CPU6502 {
this.writeByte(zpAddr, val);
const off = this.readBytePC(); // changes pc
const oldPc = this.pc;
const oldPage = oldPc >> 8;
const oldPage = oldPc & 0xff00;
let newPC = this.pc + (off > 127 ? off - 256 : off);
newPC &= 0xffff;
const newOff = newPC & 0xff;
this.readByte((oldPage << 8) | newOff);
this.readByte(oldPage | newOff);
if (((1 << b) & val) !== 0) {
this.pc = newPC;
}