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This commit is contained in:
Antoni Piasecki
2025-07-15 15:53:18 +02:00
parent 130abb5d0c
commit 16be73aadb
1 changed files with 168 additions and 16 deletions
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184
mos6502.c
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@@ -2,6 +2,7 @@
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define READ_U8() m->memory[m->pc++]
#define READ_U16() (READ_U8() | (READ_U8() << 8))
@@ -57,20 +58,30 @@ void mos6502_mem_write(MOS6502 *m, uint16_t addr, uint8_t v) {
}
void mos6502_step(MOS6502 *m) {
if (0) {
printf("$%04X: ", m->pc);
uint16_t old_pc = m->pc;
mos6502_disassemble_ins(m);
m->pc = old_pc;
printf("\tA: %02X X: %02X Y: %02X\n", m->A, m->X, m->Y);
}
uint8_t op = READ_U8();
switch (op) {
case 0x00: {
// TODO: its supposed to do some interrupt magic
exit(0);
} break;
case 0x05: {
m->A |= mos6502_mem_read(m, READ_U8());
mos6502_set_zn(m, m->A);
} break;
case 0x06: {
uint8_t addr = READ_U8();
uint8_t oper = mos6502_mem_read(m, addr);
uint8_t res = oper << 1;
mos6502_mem_write(m, addr, res);
mos6502_set_flag(m, FLAG_C, (oper >> 7) & 1);
mos6502_set_zn(m, res);
} break;
case 0x08: {
uint8_t res = m->P;
res |= (1 << 4);
res |= (1 << 5);
mos6502_mem_write(m, 0x0100 + m->SP--, res);
} break;
case 0x09: {
m->A |= READ_U8();
mos6502_set_zn(m, m->A);
@@ -81,6 +92,25 @@ void mos6502_step(MOS6502 *m) {
mos6502_set_flag(m, FLAG_C, carry);
mos6502_set_zn(m, m->A);
} break;
case 0x0D: {
m->A |= mos6502_mem_read(m, READ_U16());
mos6502_set_zn(m, m->A);
} break;
case 0x0E: {
uint16_t addr = READ_U16();
uint8_t oper = mos6502_mem_read(m, addr);
uint8_t res = oper << 1;
mos6502_mem_write(m, addr, res);
mos6502_set_flag(m, FLAG_C, (oper & 0x80) != 0);
mos6502_set_zn(m, res);
} break;
case 0x10: {
int8_t offset = READ_U8();
if (!(m->P & FLAG_N)) {
m->pc += offset;
}
} break;
case 0x18: {
mos6502_set_flag(m, FLAG_C, 0);
} break;
@@ -91,6 +121,19 @@ void mos6502_step(MOS6502 *m) {
mos6502_mem_write(m, 0x0100 + m->SP--, ret_addr & 0xFF);
m->pc = target;
} break;
case 0x24: {
uint8_t oper = mos6502_mem_read(m, READ_U8());
mos6502_set_flag(m, FLAG_Z, (m->A & oper) == 0);
mos6502_set_flag(m, FLAG_N, oper & 0x80);
mos6502_set_flag(m, FLAG_V, oper & 0x40);
} break;
case 0x25: {
m->A &= mos6502_mem_read(m, READ_U8());
mos6502_set_zn(m, m->A);
} break;
case 0x28: {
m->P = mos6502_mem_read(m, 0x0100 + (++m->SP));
} break;
case 0x29: {
m->A &= READ_U8();
mos6502_set_zn(m, m->A);
@@ -102,9 +145,38 @@ void mos6502_step(MOS6502 *m) {
mos6502_set_flag(m, FLAG_C, new_carry);
mos6502_set_zn(m, m->A);
} break;
case 0x2C: {
uint8_t oper = mos6502_mem_read(m, READ_U16());
mos6502_set_flag(m, FLAG_Z, (m->A & oper) == 0);
mos6502_set_flag(m, FLAG_N, oper & 0x80);
mos6502_set_flag(m, FLAG_V, oper & 0x40);
} break;
case 0x2D: {
m->A &= mos6502_mem_read(m, READ_U16());
mos6502_set_zn(m, m->A);
} break;
case 0x2E: {
uint16_t addr = READ_U16();
uint8_t oper = mos6502_mem_read(m, addr);
uint8_t old_carry = (m->P & FLAG_C) ? 1 : 0;
uint8_t res = (oper << 1) | old_carry;
mos6502_mem_write(m, addr, res);
mos6502_set_flag(m, FLAG_C, (oper & 0x80) >> 7);
mos6502_set_zn(m, res);
} break;
case 0x30: {
int8_t offset = READ_U8();
if (m->P & FLAG_N) {
m->pc += offset;
}
} break;
case 0x38: {
mos6502_set_flag(m, FLAG_C, 1);
} break;
case 0x45: {
m->A ^= mos6502_mem_read(m, READ_U8());
mos6502_set_zn(m, m->A);
} break;
case 0x48: {
mos6502_mem_write(m, 0x0100 + m->SP--, m->A);
} break;
@@ -120,6 +192,19 @@ void mos6502_step(MOS6502 *m) {
case 0x4C: {
m->pc = READ_U16();
} break;
case 0x4D: {
m->A ^= mos6502_mem_read(m, READ_U16());
mos6502_set_zn(m, m->A);
} break;
case 0x50: {
int8_t offset = READ_U8();
if (!(m->P & FLAG_V)) {
m->pc += offset;
}
} break;
case 0x58: {
mos6502_set_flag(m, FLAG_I, 0);
} break;
case 0x60: {
uint16_t low = mos6502_mem_read(m, 0x0100 + (++m->SP));
uint16_t high = mos6502_mem_read(m, 0x0100 + (++m->SP));
@@ -146,10 +231,9 @@ void mos6502_step(MOS6502 *m) {
m->A = res;
} break;
case 0x6A: {
uint8_t old_carry = m->P & FLAG_C;
uint8_t new_carry = m->A & 0x01;
m->A = (m->A >> 1) | (old_carry << 7);
mos6502_set_flag(m, FLAG_C, new_carry);
uint8_t carry = m->A & 0x01;
m->A = (m->A >> 1) | ((m->P & FLAG_C) << 7);
mos6502_set_flag(m, FLAG_C, carry);
mos6502_set_zn(m, m->A);
} break;
case 0x6C: {
@@ -166,6 +250,20 @@ void mos6502_step(MOS6502 *m) {
mos6502_set_zn(m, res);
m->A = res;
} break;
case 0x6E: {
uint16_t addr = READ_U16();
uint8_t oper = mos6502_mem_read(m, addr);
uint8_t res = (oper >> 1) | ((m->P & FLAG_C) << 7);
mos6502_mem_write(m, addr, res);
mos6502_set_flag(m, FLAG_C, oper & 0x01);
mos6502_set_zn(m, res);
} break;
case 0x70: {
int8_t offset = READ_U8();
if (m->P & FLAG_V) {
m->pc += offset;
}
} break;
case 0x78: {
mos6502_set_flag(m, FLAG_I, 1);
} break;
@@ -177,6 +275,9 @@ void mos6502_step(MOS6502 *m) {
m->A = m->X;
mos6502_set_zn(m, m->A);
} break;
case 0x84: {
mos6502_mem_write(m, READ_U8(), m->Y);
} break;
case 0x85: {
mos6502_mem_write(m, READ_U8(), m->A);
} break;
@@ -220,6 +321,10 @@ void mos6502_step(MOS6502 *m) {
m->X = READ_U8();
mos6502_set_zn(m, m->X);
} break;
case 0xA4: {
m->Y = mos6502_mem_read(m, READ_U8());
mos6502_set_zn(m, m->Y);
} break;
case 0xA5: {
m->A = mos6502_mem_read(m, READ_U8());
mos6502_set_zn(m, m->A);
@@ -261,6 +366,10 @@ void mos6502_step(MOS6502 *m) {
m->A = mos6502_mem_read(m, addr + m->Y);
mos6502_set_zn(m, m->A);
} break;
case 0xB5: {
m->A = mos6502_mem_read(m, READ_U8() + m->X);
mos6502_set_zn(m, m->A);
} break;
case 0xB9: {
m->A = mos6502_mem_read(m, READ_U16() + m->Y);
mos6502_set_zn(m, m->A);
@@ -315,6 +424,18 @@ void mos6502_step(MOS6502 *m) {
mos6502_set_flag(m, FLAG_C, m->X >= oper);
mos6502_set_zn(m, res);
} break;
case 0xE4: {
uint8_t oper = mos6502_mem_read(m, READ_U8());
uint16_t res = m->X - oper;
mos6502_set_flag(m, FLAG_C, m->X >= oper);
mos6502_set_zn(m, res);
} break;
case 0xEC: {
uint8_t oper = mos6502_mem_read(m, READ_U16());
uint16_t res = m->X - oper;
mos6502_set_flag(m, FLAG_C, m->X >= oper);
mos6502_set_zn(m, res);
} break;
case 0xEE: {
uint16_t addr = READ_U16();
uint8_t res = mos6502_mem_read(m, addr) + 1;
@@ -339,12 +460,23 @@ void mos6502_step(MOS6502 *m) {
m->A = res;
mos6502_set_zn(m, m->A);
} break;
case 0xED: {
uint8_t oper = mos6502_mem_read(m, READ_U16());
uint16_t res = m->A - oper - ((m->P & FLAG_C) ? 0 : 1);
mos6502_set_flag(m, FLAG_C, res < 0x100);
mos6502_set_flag(m, FLAG_V, (m->A ^ oper) & (m->A ^ res) & 0x80);
m->A = res;
mos6502_set_zn(m, m->A);
} break;
case 0xF0: {
int8_t offset = READ_U8();
if (m->P & FLAG_Z) {
m->pc += offset;
}
} break;
case 0xF8: {
mos6502_set_flag(m, FLAG_D, 1);
} break;
default:
fprintf(stderr, "unrecognized opcode: $%02X\n", op);
exit(1);
@@ -831,15 +963,28 @@ void mos6502_disassemble(MOS6502 *m, size_t program_size) {
void mos6502_free(MOS6502 m) { free(m.memory); }
int main(int argc, char *argv[]) {
if (argc < 3) {
fprintf(stderr, "Usage: %s <d|r> <path>\n", argv[0]);
const char *path = NULL;
uint8_t disassemble = 0;
uint8_t print_cpu = 0;
for (size_t i = 1; i < argc; i++) {
if (strcmp(argv[i], "-d") == 0) {
disassemble = 1;
} else if (strcmp(argv[i], "-p") == 0) {
print_cpu = 1;
} else {
path = argv[i];
}
}
if (path == NULL) {
printf("Usage: %s [-d] [-p] <path>\n", argv[0]);
return 1;
}
MOS6502 m = mos6502_create();
uint8_t buffer[1 << 16] = {0};
FILE *f = fopen(argv[2], "rb");
FILE *f = fopen(path, "rb");
size_t n = fread(buffer, 1, 1 << 16, f);
fclose(f);
@@ -847,10 +992,17 @@ int main(int argc, char *argv[]) {
m.memory[0x600 + i] = buffer[i];
}
if (argv[1][0] == 'd') {
if (disassemble) {
mos6502_disassemble(&m, n);
} else {
while (1) {
if (print_cpu) {
printf("$%04X: ", m.pc);
uint16_t old_pc = m.pc;
mos6502_disassemble_ins(&m);
m.pc = old_pc;
printf("\tA: %02X X: %02X Y: %02X\n", m.A, m.X, m.Y);
}
mos6502_step(&m);
}
}