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fixed unneeded ppu read access, causing the vram address to be incremented when it shouldnt be

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This commit is contained in:
Lauchmelder 2021-10-30 19:36:32 +02:00
parent 35b67dac5f
commit 2fdae00ff8
6 changed files with 41 additions and 11 deletions
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41
NES Emulator/cpu.c
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@ -12,7 +12,7 @@ static inline void Push(struct Bus* bus, Byte val)
static inline Byte Pop(struct Bus* bus)
{
return readBus(bus, 0x0100 + (++bus->cpu->sp));
return readBus(bus, 0x0100 + (++bus->cpu->sp), 0);
}
struct CPU* createCPU(struct Bus* parent)
@ -26,7 +26,7 @@ struct CPU* createCPU(struct Bus* parent)
// TODO: THIS IS JUST FOR THE TEST ROM
cpu->pc.word = 0xC000;
cpu->pc.word = ((Word)readBus(parent, 0xFFFD) << 8) | readBus(parent, 0xFFFC);
cpu->pc.word = ((Word)readBus(parent, 0xFFFD, 0) << 8) | readBus(parent, 0xFFFC, 0);
cpu->status.raw = 0x34;
cpu->acc = 0;
@ -94,7 +94,7 @@ int tickCPU(struct CPU* cpu)
if (cpu->remainingCycles == 0)
{
fetch(cpu);
prepareFetch(cpu);
execute(cpu);
return 1;
}
@ -107,7 +107,7 @@ void tickInstr(struct CPU* cpu)
while (!tickCPU(cpu));
}
void fetch(struct CPU* cpu)
void prepareFetch(struct CPU* cpu)
{
Byte opcodeVal = readBus(cpu->bus, cpu->pc.word);
cpu->currentOpcode = OPCODE_TABLE + opcodeVal;
@ -161,7 +161,7 @@ void fetch(struct CPU* cpu)
} break;
case IMM:
cpu->fetchedVal = readBus(cpu->bus, cpu->pc.word++);
cpu->fetchedAddress = cpu->pc.word++;
return;
case IMP:
@ -221,8 +221,12 @@ void fetch(struct CPU* cpu)
} break;
}
}
cpu->fetchedVal = readBus(cpu->bus, cpu->fetchedAddress);
void fetch(struct CPU* cpu)
{
if(cpu->currentOpcode->addr != IMP)
cpu->fetchedVal = readBus(cpu->bus, cpu->fetchedAddress);
}
void execute(struct CPU* cpu)
@ -233,6 +237,7 @@ void execute(struct CPU* cpu)
{
case ADC:
{
fetch(cpu);
Word result = cpu->acc + cpu->fetchedVal + cpu->status.carry;
cpu->status.carry = (result > 0xFF);
@ -245,6 +250,7 @@ void execute(struct CPU* cpu)
case AND:
{
fetch(cpu);
cpu->acc &= cpu->fetchedVal;
cpu->status.negative = (cpu->acc >> 7);
@ -253,6 +259,7 @@ void execute(struct CPU* cpu)
case ASL:
{
fetch(cpu);
cpu->status.carry = ((cpu->fetchedVal & 0x80) == 0x80);
cpu->fetchedVal <<= 1;
@ -379,6 +386,7 @@ void execute(struct CPU* cpu)
case BIT:
{
fetch(cpu);
cpu->status.negative = (cpu->fetchedVal >> 7);
cpu->status.overflow = (cpu->fetchedVal >> 6);
cpu->status.zero = ((cpu->acc & cpu->fetchedVal) == 0x00);
@ -415,6 +423,7 @@ void execute(struct CPU* cpu)
case CMP:
{
fetch(cpu);
Byte result = cpu->acc - cpu->fetchedVal;
cpu->status.negative = (result >> 7);
@ -424,6 +433,7 @@ void execute(struct CPU* cpu)
case CPX:
{
fetch(cpu);
Byte result = cpu->x - cpu->fetchedVal;
cpu->status.negative = (result >> 7);
@ -433,6 +443,7 @@ void execute(struct CPU* cpu)
case CPY:
{
fetch(cpu);
Byte result = cpu->y - cpu->fetchedVal;
cpu->status.negative = (result >> 7);
@ -442,6 +453,7 @@ void execute(struct CPU* cpu)
case DCP:
{
fetch(cpu);
cpu->fetchedVal--;
writeBus(cpu->bus, cpu->fetchedAddress, cpu->fetchedVal);
Byte result = cpu->acc - cpu->fetchedVal;
@ -455,6 +467,7 @@ void execute(struct CPU* cpu)
case DEC:
{
fetch(cpu);
cpu->fetchedVal--;
cpu->status.negative = ((cpu->fetchedVal & 0x80) == 0x80);
@ -481,6 +494,7 @@ void execute(struct CPU* cpu)
case EOR:
{
fetch(cpu);
cpu->acc ^= cpu->fetchedVal;
cpu->status.negative = (cpu->acc >> 7);
@ -489,6 +503,7 @@ void execute(struct CPU* cpu)
case INC:
{
fetch(cpu);
cpu->fetchedVal++;
cpu->status.negative = ((cpu->fetchedVal & 0x80) == 0x80);
@ -515,6 +530,7 @@ void execute(struct CPU* cpu)
case ISC:
{
fetch(cpu);
cpu->fetchedVal++;
writeBus(cpu->bus, cpu->fetchedAddress, cpu->fetchedVal);
Word result = cpu->acc + ~cpu->fetchedVal + cpu->status.carry;
@ -545,6 +561,7 @@ void execute(struct CPU* cpu)
case LAX:
{
fetch(cpu);
cpu->acc = cpu->fetchedVal;
cpu->x = cpu->fetchedVal;
@ -554,6 +571,7 @@ void execute(struct CPU* cpu)
case LDA:
{
fetch(cpu);
cpu->acc = cpu->fetchedVal;
cpu->status.negative = (cpu->acc >> 7);
@ -562,6 +580,7 @@ void execute(struct CPU* cpu)
case LDX:
{
fetch(cpu);
cpu->x = cpu->fetchedVal;
cpu->status.negative = (cpu->x >> 7);
@ -570,6 +589,7 @@ void execute(struct CPU* cpu)
case LDY:
{
fetch(cpu);
cpu->y = cpu->fetchedVal;
cpu->status.negative = (cpu->y >> 7);
@ -578,6 +598,7 @@ void execute(struct CPU* cpu)
case LSR:
{
fetch(cpu);
cpu->status.negative = 0;
cpu->status.carry = ((cpu->fetchedVal & 0x01) == 0x01);
@ -598,6 +619,7 @@ void execute(struct CPU* cpu)
case ORA:
{
fetch(cpu);
cpu->acc |= cpu->fetchedVal;
cpu->status.negative = (cpu->acc >> 7);
@ -630,6 +652,7 @@ void execute(struct CPU* cpu)
case RLA:
{
fetch(cpu);
Byte oldCarry = cpu->status.carry;
cpu->status.carry = ((cpu->fetchedVal & 0x80) == 0x80);
@ -647,6 +670,7 @@ void execute(struct CPU* cpu)
case ROL:
{
fetch(cpu);
Byte oldCarry = cpu->status.carry;
cpu->status.carry = ((cpu->fetchedVal & 0x80) == 0x80);
@ -664,6 +688,7 @@ void execute(struct CPU* cpu)
case ROR:
{
fetch(cpu);
Byte oldCarry = cpu->status.carry;
cpu->status.negative = oldCarry;
cpu->status.carry = ((cpu->fetchedVal & 0x01) == 0x01);
@ -681,6 +706,7 @@ void execute(struct CPU* cpu)
case RRA:
{
fetch(cpu);
Byte oldCarry = cpu->status.carry;
cpu->status.carry = ((cpu->fetchedVal & 0x01) == 0x01);
@ -722,6 +748,7 @@ void execute(struct CPU* cpu)
case SBC:
{
fetch(cpu);
Word result = cpu->acc + ~cpu->fetchedVal + cpu->status.carry;
cpu->status.carry = ((result & 0x8000) != 0x8000);
@ -749,6 +776,7 @@ void execute(struct CPU* cpu)
case SLO:
{
fetch(cpu);
cpu->status.carry = ((cpu->fetchedVal & 0x80) == 0x80);
cpu->fetchedVal <<= 1;
@ -764,6 +792,7 @@ void execute(struct CPU* cpu)
case SRE:
{
fetch(cpu);
cpu->status.carry = ((cpu->fetchedVal & 0x01) == 0x01);
cpu->fetchedVal >>= 1;