158 lines
3.6 KiB
C
158 lines
3.6 KiB
C
// https://www.masswerk.at/6502/6502_instruction_set.html
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// https://tutorial-6502.sourceforge.io/specification/opcodes/
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#include <stdint.h>
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#include <stdio.h>
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#include <stdlib.h>
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#define READ_ADDR() \
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uint16_t low = m->memory[m->pc++]; \
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uint16_t high = m->memory[m->pc++]; \
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uint16_t addr = (high << 8) | low
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typedef struct MOS6502 {
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uint8_t *memory;
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uint16_t pc;
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// TODO
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// uint8_t A;
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// uint8_t X;
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// uint8_t Y;
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// uint8_t SP;
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// uint8_t P;
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} MOS6502;
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MOS6502 mos6502_create() {
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MOS6502 m = {0};
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m.pc = 0x600;
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m.memory = calloc(1, 1 << 16);
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return m;
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}
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void mos6502_disassemble(MOS6502 *m, size_t ins_count) {
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for (size_t i = 0; i < ins_count; i++) {
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printf("%04X: ", m->pc);
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uint8_t op = m->memory[m->pc++];
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switch (op) {
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case 0x00: {
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printf("BRK\n");
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} break;
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case 0x18: {
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printf("CLC\n");
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} break;
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case 0x20: {
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READ_ADDR();
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printf("JSR $%04X\n", addr);
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} break;
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case 0x38: {
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printf("SEC\n");
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} break;
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case 0x4C: {
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READ_ADDR();
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printf("JMP $%04X\n", addr);
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} break;
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case 0x60: {
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printf("RTS\n");
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} break;
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case 0x69: {
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printf("ADC #$%02X\n", m->memory[m->pc++]);
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} break;
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case 0x85: {
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printf("STA #$%02X\n", m->memory[m->pc++]);
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} break;
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case 0x8C: {
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READ_ADDR();
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printf("STY $%04X\n", addr);
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} break;
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case 0x8D: {
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READ_ADDR();
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printf("STA $%04X\n", addr);
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} break;
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case 0x8E: {
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READ_ADDR();
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printf("STX $%04X\n", addr);
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} break;
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case 0x90: {
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int8_t offset = m->memory[m->pc++];
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printf("BCC $%04X\n", m->pc + offset);
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} break;
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case 0x99: {
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READ_ADDR();
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printf("STA $%04X,Y\n", addr);
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} break;
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case 0xA0: {
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printf("LDY #$%02X\n", m->memory[m->pc++]);
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} break;
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case 0xA2: {
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printf("LDX #$%02X\n", m->memory[m->pc++]);
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} break;
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case 0xA9: {
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printf("LDA #$%02X\n", m->memory[m->pc++]);
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} break;
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case 0xAD: {
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READ_ADDR();
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printf("LDA $%04X\n", addr);
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} break;
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case 0xB0: {
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int8_t offset = m->memory[m->pc++];
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printf("BCS $%04X\n", m->pc + offset);
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} break;
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case 0xB1: {
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printf("LDA (#$%02X),Y\n", m->memory[m->pc++]);
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} break;
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case 0xBD: {
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READ_ADDR();
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printf("LDA $%04X,X\n", addr);
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} break;
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case 0xC8: {
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printf("INY\n");
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} break;
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case 0xC9: {
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printf("CMP #$%02X\n", m->memory[m->pc++]);
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} break;
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case 0xD0: {
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int8_t offset = m->memory[m->pc++];
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printf("BNE $%04X\n", m->pc + offset);
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} break;
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case 0xE0: {
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printf("CPX #$%02X\n", m->memory[m->pc++]);
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} break;
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case 0xE8: {
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printf("INX\n");
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} break;
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case 0xE9: {
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printf("SBC #$%02X\n", m->memory[m->pc++]);
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} break;
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case 0xF0: {
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int8_t offset = m->memory[m->pc++];
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printf("BEQ $%04X\n", m->pc + offset);
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} break;
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default:
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fprintf(stderr, "unrecognized opcode: %x\n", op);
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exit(1);
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}
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}
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}
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void mos6502_free(MOS6502 m) { free(m.memory); }
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int main(int argc, char *argv[]) {
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if (argc < 2) {
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fprintf(stderr, "Usage: %s <path>\n", argv[0]);
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return 1;
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}
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MOS6502 m = mos6502_create();
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uint8_t buffer[4000] = {0};
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FILE *f = fopen(argv[1], "rb");
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size_t n = fread(buffer, 1, 4000, f);
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fclose(f);
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for (size_t i = 0; i < n; i++) {
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m.memory[0x600 + i] = buffer[i];
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}
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mos6502_disassemble(&m, 103);
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mos6502_free(m);
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} |