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even more opcodes

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This commit is contained in:
Antoni Piasecki
2025-07-15 14:28:01 +02:00
parent 0004a7b4c6
commit 130abb5d0c
1 changed files with 95 additions and 8 deletions
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103
mos6502.c
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@@ -1,5 +1,4 @@
// https://www.masswerk.at/6502/6502_instruction_set.html
// https://tutorial-6502.sourceforge.io/specification/opcodes/
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
@@ -52,7 +51,8 @@ uint8_t mos6502_mem_read(MOS6502 *m, uint16_t addr) { return m->memory[addr]; }
void mos6502_mem_write(MOS6502 *m, uint16_t addr, uint8_t v) {
m->memory[addr] = v;
if (addr == 0x0400) {
putchar(m->memory[addr]);
printf("%c", m->memory[addr]);
fflush(stdout);
}
}
@@ -125,6 +125,14 @@ void mos6502_step(MOS6502 *m) {
uint16_t high = mos6502_mem_read(m, 0x0100 + (++m->SP));
m->pc = (((uint16_t)high << 8) | low) + 1;
} break;
case 0x65: {
uint8_t oper = mos6502_mem_read(m, READ_U8());
uint16_t res = m->A + oper + (m->P & FLAG_C);
mos6502_set_flag(m, FLAG_C, res > 0xFF);
mos6502_set_flag(m, FLAG_V, (~(m->A ^ oper) & (m->A ^ res) & 0x80) != 0);
mos6502_set_zn(m, res);
m->A = res;
} break;
case 0x68: {
m->A = mos6502_mem_read(m, 0x0100 + (++m->SP));
mos6502_set_zn(m, m->A);
@@ -134,8 +142,8 @@ void mos6502_step(MOS6502 *m) {
uint16_t res = m->A + oper + (m->P & FLAG_C);
mos6502_set_flag(m, FLAG_C, res > 0xFF);
mos6502_set_flag(m, FLAG_V, (~(m->A ^ oper) & (m->A ^ res) & 0x80) != 0);
mos6502_set_zn(m, res);
m->A = res;
mos6502_set_zn(m, m->A);
} break;
case 0x6A: {
uint8_t old_carry = m->P & FLAG_C;
@@ -144,13 +152,40 @@ void mos6502_step(MOS6502 *m) {
mos6502_set_flag(m, FLAG_C, new_carry);
mos6502_set_zn(m, m->A);
} break;
case 0x6C: {
uint16_t oper = READ_U16();
uint16_t addr =
mos6502_mem_read(m, oper) | (mos6502_mem_read(m, oper + 1) << 8);
m->pc = addr;
} break;
case 0x6D: {
uint8_t oper = mos6502_mem_read(m, READ_U16());
uint16_t res = m->A + oper + (m->P & FLAG_C);
mos6502_set_flag(m, FLAG_C, res > 0xFF);
mos6502_set_flag(m, FLAG_V, (~(m->A ^ oper) & (m->A ^ res) & 0x80) != 0);
mos6502_set_zn(m, res);
m->A = res;
} break;
case 0x78: {
mos6502_set_flag(m, FLAG_I, 1);
} break;
case 0x88: {
m->Y--;
mos6502_set_zn(m, m->Y);
} break;
case 0x8A: {
m->A = m->X;
mos6502_set_zn(m, m->A);
} break;
case 0x85: {
mos6502_mem_write(m, READ_U8(), m->A);
} break;
case 0x8D: {
mos6502_mem_write(m, READ_U16(), m->A);
} break;
case 0x8E: {
mos6502_mem_write(m, READ_U16(), m->X);
} break;
case 0x90: {
int8_t offset = READ_U8();
if (!(m->P & FLAG_C)) {
@@ -164,6 +199,9 @@ void mos6502_step(MOS6502 *m) {
case 0x99: {
mos6502_mem_write(m, READ_U16() + m->Y, m->A);
} break;
case 0x9A: {
m->SP = m->X;
} break;
case 0x9D: {
mos6502_mem_write(m, READ_U16() + m->X, m->A);
} break;
@@ -171,14 +209,29 @@ void mos6502_step(MOS6502 *m) {
m->Y = READ_U8();
mos6502_set_zn(m, m->Y);
} break;
case 0xA1: {
uint8_t oper = READ_U8() + m->X;
uint16_t addr = mos6502_mem_read(m, oper) |
(mos6502_mem_read(m, (oper + 1 & 0xFF)) << 8);
m->A = mos6502_mem_read(m, addr);
mos6502_set_zn(m, m->A);
} break;
case 0xA2: {
m->X = READ_U8();
mos6502_set_zn(m, m->X);
} break;
case 0xA8: {
m->X = m->A;
case 0xA5: {
m->A = mos6502_mem_read(m, READ_U8());
mos6502_set_zn(m, m->A);
} break;
case 0xA6: {
m->X = mos6502_mem_read(m, READ_U8());
mos6502_set_zn(m, m->X);
} break;
case 0xA8: {
m->Y = m->A;
mos6502_set_zn(m, m->Y);
} break;
case 0xA9: {
m->A = READ_U8();
mos6502_set_zn(m, m->A);
@@ -191,12 +244,23 @@ void mos6502_step(MOS6502 *m) {
m->A = mos6502_mem_read(m, READ_U16());
mos6502_set_zn(m, m->A);
} break;
case 0xAE: {
m->X = mos6502_mem_read(m, READ_U16());
mos6502_set_zn(m, m->X);
} break;
case 0xB0: {
int8_t offset = READ_U8();
if (m->P & FLAG_C) {
m->pc += offset;
}
} break;
case 0xB1: {
uint8_t oper = READ_U8();
uint16_t addr = mos6502_mem_read(m, oper) |
(mos6502_mem_read(m, (oper + 1 & 0xFF)) << 8);
m->A = mos6502_mem_read(m, addr + m->Y);
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);
@@ -205,6 +269,18 @@ void mos6502_step(MOS6502 *m) {
m->A = mos6502_mem_read(m, READ_U16() + m->X);
mos6502_set_zn(m, m->A);
} break;
case 0xC0: {
uint8_t oper = READ_U8();
uint16_t res = m->Y - oper;
mos6502_set_flag(m, FLAG_C, m->Y >= oper);
mos6502_set_zn(m, res);
} break;
case 0xC6: {
uint16_t addr = READ_U8();
uint8_t res = mos6502_mem_read(m, addr) - 1;
mos6502_mem_write(m, addr, res);
mos6502_set_zn(m, res);
} break;
case 0xC8: {
m->Y++;
mos6502_set_zn(m, m->Y);
@@ -230,6 +306,9 @@ void mos6502_step(MOS6502 *m) {
m->pc += offset;
}
} break;
case 0xD8: {
mos6502_set_flag(m, FLAG_D, 0);
} break;
case 0xE0: {
uint8_t oper = READ_U8();
uint16_t res = m->X - oper;
@@ -242,6 +321,12 @@ void mos6502_step(MOS6502 *m) {
mos6502_mem_write(m, addr, res);
mos6502_set_zn(m, res);
} break;
case 0xE6: {
uint16_t addr = READ_U8();
uint8_t res = mos6502_mem_read(m, addr) + 1;
mos6502_mem_write(m, addr, res);
mos6502_set_zn(m, res);
} break;
case 0xE8: {
m->X++;
mos6502_set_zn(m, m->X);
@@ -493,13 +578,13 @@ void mos6502_disassemble_ins(MOS6502 *m) {
printf("STA ($%02X,X)", READ_U8());
} break;
case 0x84: {
printf("STY $%02X", READ_U8());
printf("STY $%02X\t", READ_U8());
} break;
case 0x85: {
printf("STA $%02X", READ_U8());
printf("STA $%02X\t", READ_U8());
} break;
case 0x86: {
printf("STX $%02X", READ_U8());
printf("STX $%02X\t", READ_U8());
} break;
case 0x88: {
printf("DEY\t");
@@ -769,4 +854,6 @@ int main(int argc, char *argv[]) {
mos6502_step(&m);
}
}
mos6502_free(m);
}