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Use correct boundary crossing conditional for Read/Modify/Write Absolute,X addressing mode.

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Signed-off-by: Adrian Conlon <Adrian.conlon@gmail.com>
This commit is contained in:
Adrian Conlon 2019-01-06 12:58:13 +00:00
parent baf32cef89
commit 4d3be9e756
2 changed files with 11 additions and 9 deletions
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4
M6502/inc/mos6502.h
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@ -92,10 +92,12 @@ namespace EightBit {
// Addressing modes, read
enum PageCrossingBehavior { AlwaysReadTwice, MaybeReadTwice };
uint8_t AM_Immediate();
uint8_t AM_Absolute();
uint8_t AM_ZeroPage();
uint8_t AM_AbsoluteX();
uint8_t AM_AbsoluteX(PageCrossingBehavior behaviour = MaybeReadTwice);
uint8_t AM_AbsoluteY();
uint8_t AM_ZeroPageX();
uint8_t AM_ZeroPageY();

16
M6502/src/mos6502.cpp
View File

@ -127,7 +127,7 @@ int EightBit::MOS6502::execute() {
case 0x1b: slo(AM_AbsoluteY()); break; // *SLO (absolute, Y)
case 0x1c: AM_AbsoluteX(); break; // *NOP (absolute, X)
case 0x1d: A() = orr(A(), AM_AbsoluteX()); break; // ORA (absolute, X)
case 0x1e: addCycle(); busReadModifyWrite(asl(AM_AbsoluteX())); break; // ASL (absolute, X)
case 0x1e: busReadModifyWrite(asl(AM_AbsoluteX(AlwaysReadTwice))); break; // ASL (absolute, X)
case 0x1f: slo(AM_AbsoluteX()); break; // *SLO (absolute, X)
case 0x20: jsr(); break; // JSR (absolute)
@ -161,7 +161,7 @@ int EightBit::MOS6502::execute() {
case 0x3b: rla(AM_AbsoluteY()); break; // *RLA (absolute, Y)
case 0x3c: AM_AbsoluteX(); break; // *NOP (absolute, X)
case 0x3d: A() = andr(A(), AM_AbsoluteX()); break; // AND (absolute, X)
case 0x3e: addCycle(); busReadModifyWrite(rol(AM_AbsoluteX())); break; // ROL (absolute, X)
case 0x3e: busReadModifyWrite(rol(AM_AbsoluteX(AlwaysReadTwice))); break; // ROL (absolute, X)
case 0x3f: rla(AM_AbsoluteX()); break; // *RLA (absolute, X)
case 0x40: busRead(); rti(); break; // RTI (implied)
@ -195,7 +195,7 @@ int EightBit::MOS6502::execute() {
case 0x5b: sre(AM_AbsoluteY()); break; // *SRE (absolute, Y)
case 0x5c: AM_AbsoluteX(); break; // *NOP (absolute, X)
case 0x5d: A() = eorr(A(), AM_AbsoluteX()); break; // EOR (absolute, X)
case 0x5e: addCycle(); busReadModifyWrite(lsr(AM_AbsoluteX())); break; // LSR (absolute, X)
case 0x5e: busReadModifyWrite(lsr(AM_AbsoluteX(AlwaysReadTwice))); break; // LSR (absolute, X)
case 0x5f: sre(AM_AbsoluteX()); break; // *SRE (absolute, X)
case 0x60: busRead(); rts(); break; // RTS (implied)
@ -229,7 +229,7 @@ int EightBit::MOS6502::execute() {
case 0x7b: rra(AM_AbsoluteY()); break; // *RRA (absolute, Y)
case 0x7c: AM_AbsoluteX(); break; // *NOP (absolute, X)
case 0x7d: A() = adc(A(), AM_AbsoluteX()); break; // ADC (absolute, X)
case 0x7e: addCycle(); busReadModifyWrite(ror(AM_AbsoluteX())); break; // ROR (absolute, X)
case 0x7e: busReadModifyWrite(ror(AM_AbsoluteX(AlwaysReadTwice))); break; // ROR (absolute, X)
case 0x7f: rra(AM_AbsoluteX()); break; // *RRA (absolute, X)
case 0x80: AM_Immediate(); break; // *NOP (immediate)
@ -331,7 +331,7 @@ int EightBit::MOS6502::execute() {
case 0xdb: dcp(AM_AbsoluteY()); break; // *DCP (absolute, Y)
case 0xdc: AM_AbsoluteX(); break; // *NOP (absolute, X)
case 0xdd: cmp(A(), AM_AbsoluteX()); break; // CMP (absolute, X)
case 0xde: addCycle(); busReadModifyWrite(dec(AM_AbsoluteX())); break; // DEC (absolute, X)
case 0xde: busReadModifyWrite(dec(AM_AbsoluteX(AlwaysReadTwice))); break; // DEC (absolute, X)
case 0xdf: dcp(AM_AbsoluteX()); break; // *DCP (absolute, X)
case 0xe0: cmp(X(), AM_Immediate()); break; // CPX (immediate)
@ -365,7 +365,7 @@ int EightBit::MOS6502::execute() {
case 0xfb: isb(AM_AbsoluteY()); break; // *ISB (absolute, Y)
case 0xfc: AM_AbsoluteX(); break; // *NOP (absolute, X)
case 0xfd: A() = sbc(A(), AM_AbsoluteX()); break; // SBC (absolute, X)
case 0xfe: addCycle(); busReadModifyWrite(inc(AM_AbsoluteX())); break; // INC (absolute, X)
case 0xfe: busReadModifyWrite(inc(AM_AbsoluteX(AlwaysReadTwice))); break; // INC (absolute, X)
case 0xff: isb(AM_AbsoluteX()); break; // *ISB (absolute, X)
}
@ -457,10 +457,10 @@ uint8_t EightBit::MOS6502::AM_ZeroPage() {
return Processor::busRead(Address_ZeroPage());
}
uint8_t EightBit::MOS6502::AM_AbsoluteX() {
uint8_t EightBit::MOS6502::AM_AbsoluteX(const PageCrossingBehavior behaviour) {
const auto [address, page] = Address_AbsoluteX();
auto possible = getBytePaged(page, address.low);
if (UNLIKELY(page != address.high))
if ((behaviour == AlwaysReadTwice) || UNLIKELY(page != address.high))
possible = Processor::busRead(address);
return possible;
}