193 lines
3.3 KiB
C
193 lines
3.3 KiB
C
#include "cpu.h"
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#include <stdlib.h>
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#include <stdio.h>
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#include "log.h"
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#include "bus.h"
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struct CPU* createCPU(struct Bus* parent)
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{
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struct CPU* cpu = (struct CPU*)malloc(sizeof(struct CPU));
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if (cpu == NULL)
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{
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fprintf(stderr, "Failed to create CPU, aborting.\n");
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exit(1);
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}
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// TODO: THIS IS JUST FOR THE TEST ROM
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cpu->pc = 0xC000;
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cpu->status.raw = 0x34;
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cpu->acc = 0;
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cpu->x = 0;
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cpu->y = 0;
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cpu->remainingCycles = 7;
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cpu->totalCycles = 0;
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cpu->bus = parent;
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return cpu;
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}
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void destroyCPU(struct CPU* cpu)
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{
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free(cpu);
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}
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int tickCPU(struct CPU* cpu)
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{
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cpu->remainingCycles--;
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cpu->totalCycles += 1;
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if (cpu->remainingCycles == 0)
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{
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fetch(cpu);
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execute(cpu);
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return 1;
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}
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return 0;
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}
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void tickInstr(struct CPU* cpu)
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{
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while (!tickCPU(cpu));
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}
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void fetch(struct CPU* cpu)
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{
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Byte opcodeVal = readBus(cpu->bus, cpu->pc++);
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cpu->currentOpcode = OPCODE_TABLE + opcodeVal;
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if (cpu->currentOpcode->op == XXX)
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{
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fprintf(stderr, "Unknown opcode: %x", opcodeVal);
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exit(1);
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}
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cpu->remainingCycles = cpu->currentOpcode->cycles;
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switch (cpu->currentOpcode->addr)
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{
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case ACC:
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cpu->fetchedVal = cpu->acc;
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break;
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case ABS:
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{
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Byte lo = readBus(cpu->bus, cpu->pc++);
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Byte hi = readBus(cpu->bus, cpu->pc++);
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cpu->fetchedAddress = ((Word)hi << 8) | lo;
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} break;
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case ABX:
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{
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Byte lo = readBus(cpu->bus, cpu->pc++);
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Byte hi = readBus(cpu->bus, cpu->pc++);
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Word addr = ((Word)hi << 8) | lo;
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cpu->fetchedAddress = addr + cpu->x;
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if ((cpu->fetchedAddress & 0xFF00) != (addr & 0xFF00))
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cpu->remainingCycles++;
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} break;
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case ABY:
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{
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Byte lo = readBus(cpu->bus, cpu->pc++);
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Byte hi = readBus(cpu->bus, cpu->pc++);
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Word addr = ((Word)hi << 8) | lo;
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cpu->fetchedAddress = addr + cpu->y;
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if ((cpu->fetchedAddress & 0xFF00) != (addr & 0xFF00))
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cpu->remainingCycles++;
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} break;
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case IMM:
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cpu->fetchedVal = readBus(cpu->bus, cpu->pc++);
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break;
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case IMP:
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break;
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case IND:
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{
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Byte lo = readBus(cpu->bus, cpu->pc++);
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Byte hi = readBus(cpu->bus, cpu->pc++);
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Word addr = ((Word)hi << 8) | lo;
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cpu->fetchedAddress = readBus(cpu->bus, addr);
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} break;
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case INDX:
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{
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Byte op = readBus(cpu->bus, cpu->pc++);
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Byte lo = readBus(cpu->bus, op + cpu->x);
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Byte hi = readBus(cpu->bus, op + cpu->x + 1);
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Word addr = ((Word)hi << 8) | lo;
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cpu->fetchedAddress = readBus(cpu->bus, addr);
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} break;
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case INDY:
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{
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Byte op = readBus(cpu->bus, cpu->pc++);
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Byte lo = readBus(cpu->bus, op);
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Byte hi = readBus(cpu->bus, op + 1);
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Word addr = ((Word)hi << 8) | lo;
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addr = readBus(cpu->bus, addr);
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cpu->fetchedAddress = addr + cpu->y;
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if ((cpu->fetchedAddress & 0xFF00) != (addr & 0xFF00))
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cpu->remainingCycles++;
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} break;
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case REL:
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{
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cpu->fetchedRelAddress = readBus(cpu->bus, cpu->pc++);
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} break;
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case ZPG:
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cpu->fetchedAddress = readBus(cpu->bus, cpu->pc++);
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break;
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case ZPX:
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{
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cpu->fetchedAddress = readBus(cpu->bus, cpu->pc++) + cpu->x;
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cpu->fetchedAddress |= 0xFF;
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} break;
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case ZPY:
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{
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cpu->fetchedAddress = readBus(cpu->bus, cpu->pc++) + cpu->y;
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cpu->fetchedAddress |= 0xFF;
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} break;
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}
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}
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void execute(struct CPU* cpu)
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{
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LOG_BUS(cpu->bus);
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switch (cpu->currentOpcode->op)
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{
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case JMP:
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{
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cpu->pc = cpu->fetchedAddress;
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} break;
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default:
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fprintf(stderr, "Unknown instruction: %s", cpu->currentOpcode->str);
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exit(1);
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break;
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}
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}
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