6502/src/emu.c

#include "constants.h"

#include <stdint.h>
#include <stdio.h>
#include <unistd.h>

void memview() {
	for (int i = 0x00; i <= 0xFFFF; i++) {
		if (memory[i] != 0x00) {
			//printf("Mem Address 0x%04X: 0x%04X\n", i, memory[i]);
		}
	}
	printf("irx - %d\n", irx);
	printf("iry - %d\n", iry);
	printf("acc - %d\n", acc);
}

int emulate(uint8_t exec[], int size, uint8_t addr) {
	//uint8_t* program = (uint8_t*)exec;
	for (int i = addr, i2=0; i < size+addr; i++) {
		memory[i] = exec[i2];
		i2++;
	}

	while (prc < size) {
		uint8_t inst = memory[addr+prc];
		switch (inst) {
			//BRK
			case 0x00:
				cpuStatus.brk = 0x01;
				prc++;
				prc++;
				break;
			//NOP
			case 0xEA:
				prc++;
				break;
			case 0x80:
				prc++;
				break;

			//variations on an INC
			case 0xE6:
				memory[memory[++prc+addr]]++;
				prc++;
				break;
			case 0xE8:
				irx++;
				prc++;
				break;
			case 0xC8:
				iry++;
				prc++;
				break;

			//LDA
			case 0xA9: {
				uint8_t mem = memory[memory[++prc+addr]];
				acc = mem;
				prc++;
				break;
			}
			case 0xA5: {
				uint8_t mem = memory[memory[++prc+addr]];
				acc = mem;
				prc++;
				break;
			}
			case 0xB1: {
				uint8_t mem = memory[(++prc)+addr];
				mem+=iry;
				acc = memory[mem];
				prc++;
				break;
			}

			//STA
			case 0x85: {
				memory[memory[++prc+addr]] = acc;
				prc++;
				break;
			}

			//STY
			case 0x84: {
				memory[memory[++prc+addr]] = iry;
				prc++;
				break;
			}

			//variations on an LDY (it doesn't work as well the second time)
			case 0xA0: {
				uint8_t mem = memory[memory[++prc+addr]];
				iry = mem;
				prc++;
				break;
			}

			//ORA
			case 0x01: {
				uint8_t mem = memory[(++prc)+addr];
				mem+=irx;
				uint8_t val = memory[mem];
				acc = acc | val;
				prc++;
				break;
			}

			//TAX
			case 0xAA: {
				irx = acc;
				if (irx == 0) {
					cpuStatus.zero = 1;
				} else {
					cpuStatus.zero = 0;
				}
				prc++;
				break;
			}

			//DEX
			case 0xCA: {
				irx--;
				if (irx == 0) {
					cpuStatus.zero = 1;
				} else {
					cpuStatus.zero = 0;
				}
				prc++;
				break;
			}
			case 0xD1: {
				uint8_t mem = memory[(++prc)+addr];
				mem+=iry;
				mem = memory[mem];
				if (acc >= mem) {
					cpuStatus.carry = 1;
				} else {
					cpuStatus.carry = 0;
				}

				if (acc == mem) {
					cpuStatus.zero = 1;
				} else {
					cpuStatus.zero = 0;
				}
				prc++;
				break;
			}


			case 0x90: {
				uint8_t mem = memory[memory[++prc+addr]];
				if (cpuStatus.carry == 0x00) {
					prc += mem;
				}
				break;
			}
			case 0x10: {
				uint8_t mem = memory[memory[++prc+addr]];
				if (cpuStatus.neg == 0x00) {
					prc += mem;
				}
				break;
			}
			case 0xF0: {
				uint8_t mem = memory[memory[++prc+addr]];
				if (cpuStatus.zero == 0x00) {
					prc += mem;
				}
				break;
			}

			default:
				printf("Opcode 0x%02X\n not implemented!\n", inst);
				_exit(0);
		}
		printf("Ran inst 0x%02X\n", inst);
		memview();
	}

	return 0;
}