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chip8_core.c
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/*
* Copyright (C) 2015 Richard Burke
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include "chip8_core.h"
#include "chip8.h"
#define C8_REG_V_IDX(instruction) (((instruction) & 0x0F00) >> 8)
#define C8_REG_V2_IDX(instruction) (((instruction) & 0x00F0) >> 4)
#define C8_INSTR_VALUE(instruction) ((instruction) & 0x00FF)
static uint16_t c8_fetch_next_instruction(const Chip8 *);
static void execute_instruction(Chip8 *, uint16_t);
static const uint8_t c8_builtin_sprites[] = {
0xF0, 0x90, 0x90, 0x90, 0xF0,
0x20, 0x60, 0x20, 0x20, 0x70,
0xF0, 0x10, 0xF0, 0x80, 0xF0,
0xF0, 0x10, 0xF0, 0x10, 0xF0,
0x90, 0x90, 0xF0, 0x10, 0x10,
0xF0, 0x80, 0xF0, 0x10, 0xF0,
0xF0, 0x80, 0xF0, 0x90, 0xF0,
0xF0, 0x10, 0x20, 0x40, 0x40,
0xF0, 0x90, 0xF0, 0x90, 0xF0,
0xF0, 0x90, 0xF0, 0x10, 0xF0,
0xF0, 0x90, 0xF0, 0x90, 0x90,
0xE0, 0x90, 0xE0, 0x90, 0xE0,
0xF0, 0x80, 0x80, 0x80, 0xF0,
0xE0, 0x90, 0x90, 0x90, 0xE0,
0xF0, 0x80, 0xF0, 0x80, 0xF0,
0xF0, 0x80, 0xF0, 0x80, 0x80
};
void c8_init(Chip8 *chip8)
{
memset(chip8, 0, sizeof(Chip8));
chip8->program_counter = C8_PROGRAM_MEMORY_START;
chip8->display_height = C8_DISPLAY_HEIGHT;
chip8->display_width = C8_DISPLAY_WIDTH;
chip8->wait_key_V_reg = -1;
memcpy(chip8->memory, c8_builtin_sprites, sizeof(c8_builtin_sprites));
srand(time(NULL));
}
void c8_run_cycle(Chip8 *chip8)
{
uint16_t instr = c8_fetch_next_instruction(chip8);
execute_instruction(chip8, instr);
}
static uint16_t c8_fetch_next_instruction(const Chip8 *chip8)
{
/* Instructions are 2 bytes long and stored most significant byte first */
return chip8->memory[chip8->program_counter] << 8 |
chip8->memory[chip8->program_counter + 1];
}
static void execute_instruction(Chip8 *chip8, uint16_t instr)
{
/* See http://devernay.free.fr/hacks/chip8/C8TECH10.HTM#3.1
* for a description of CHIP-8 instructions */
switch (instr & 0xF000) {
case 0x0: {
switch (instr) {
case 0x00E0: {
memset(chip8->display, 0, sizeof(chip8->display));
chip8->update_display = true;
chip8->program_counter += 2;
return;
}
case 0x00EE: {
chip8->program_counter = chip8->stack[--chip8->stack_pointer];
chip8->program_counter += 2;
return;
}
default: {
break;
}
}
}
case 0x1000: {
chip8->program_counter = instr & 0x0FFF;
return;
}
case 0x2000: {
chip8->stack[chip8->stack_pointer++] = chip8->program_counter;
chip8->program_counter = instr & 0x0FFF;
return;
}
case 0x3000: {
if (chip8->register_V[C8_REG_V_IDX(instr)] == C8_INSTR_VALUE(instr)) {
chip8->program_counter += 4;
} else {
chip8->program_counter += 2;
}
return;
}
case 0x4000: {
if (chip8->register_V[C8_REG_V_IDX(instr)] != C8_INSTR_VALUE(instr)) {
chip8->program_counter += 4;
} else {
chip8->program_counter += 2;
}
return;
}
case 0x5000: {
if (chip8->register_V[C8_REG_V_IDX(instr)] == chip8->register_V[C8_REG_V2_IDX(instr)]) {
chip8->program_counter += 4;
} else {
chip8->program_counter += 2;
}
return;
}
case 0x6000: {
chip8->register_V[C8_REG_V_IDX(instr)] = C8_INSTR_VALUE(instr);
chip8->program_counter += 2;
return;
}
case 0x7000: {
chip8->register_V[C8_REG_V_IDX(instr)] += C8_INSTR_VALUE(instr);
chip8->program_counter += 2;
return;
}
case 0x8000: {
switch (instr & 0x000F) {
case 0x0: {
chip8->register_V[C8_REG_V_IDX(instr)] = chip8->register_V[C8_REG_V2_IDX(instr)];
chip8->program_counter += 2;
return;
}
case 0x1: {
chip8->register_V[C8_REG_V_IDX(instr)] |= chip8->register_V[C8_REG_V2_IDX(instr)];
chip8->program_counter += 2;
return;
}
case 0x2: {
chip8->register_V[C8_REG_V_IDX(instr)] &= chip8->register_V[C8_REG_V2_IDX(instr)];
chip8->program_counter += 2;
return;
}
case 0x3: {
chip8->register_V[C8_REG_V_IDX(instr)] ^= chip8->register_V[C8_REG_V2_IDX(instr)];
chip8->program_counter += 2;
return;
}
case 0x4: {
uint8_t value1 = chip8->register_V[C8_REG_V_IDX(instr)];
uint8_t value2 = chip8->register_V[C8_REG_V2_IDX(instr)];
if (value1 > UINT8_MAX - value2) {
chip8->register_V[0xF] = 1;
} else {
chip8->register_V[0xF] = 0;
}
chip8->register_V[C8_REG_V_IDX(instr)] = value1 + value2;
chip8->program_counter += 2;
return;
}
case 0x5: {
uint8_t value1 = chip8->register_V[C8_REG_V_IDX(instr)];
uint8_t value2 = chip8->register_V[C8_REG_V2_IDX(instr)];
if (value1 > value2) {
chip8->register_V[0xF] = 1;
} else {
chip8->register_V[0xF] = 0;
}
chip8->register_V[C8_REG_V_IDX(instr)] = value1 - value2;
chip8->program_counter += 2;
return;
}
case 0x6: {
uint8_t value = chip8->register_V[C8_REG_V_IDX(instr)];
if (value & 0x1) {
chip8->register_V[0xF] = 1;
} else {
chip8->register_V[0xF] = 0;
}
chip8->register_V[C8_REG_V_IDX(instr)] /= 2;
chip8->program_counter += 2;
return;
}
case 0x7: {
uint8_t value1 = chip8->register_V[C8_REG_V_IDX(instr)];
uint8_t value2 = chip8->register_V[C8_REG_V2_IDX(instr)];
if (value2 > value1) {
chip8->register_V[0xF] = 1;
} else {
chip8->register_V[0xF] = 0;
}
chip8->register_V[C8_REG_V_IDX(instr)] = value2 - value1;
chip8->program_counter += 2;
return;
}
case 0xE: {
uint8_t value = chip8->register_V[C8_REG_V_IDX(instr)];
if (value & 0x80) {
chip8->register_V[0xF] = 1;
} else {
chip8->register_V[0xF] = 0;
}
chip8->register_V[C8_REG_V_IDX(instr)] *= 2;
chip8->program_counter += 2;
return;
}
default: {
break;
}
}
}
case 0x9000: {
if (chip8->register_V[C8_REG_V_IDX(instr)] != chip8->register_V[C8_REG_V2_IDX(instr)]) {
chip8->program_counter += 4;
} else {
chip8->program_counter += 2;
}
return;
}
case 0xA000: {
chip8->register_I = (instr & 0x0FFF);
chip8->program_counter += 2;
return;
}
case 0xB000: {
chip8->program_counter = (instr & 0x0FFF) + chip8->register_V[0];
return;
}
case 0xC000: {
chip8->register_V[C8_REG_V_IDX(instr)] = (rand() % UINT8_MAX) & C8_INSTR_VALUE(instr);
chip8->program_counter += 2;
return;
}
case 0xD000: {
uint8_t x = chip8->register_V[C8_REG_V_IDX(instr)];
uint8_t y = chip8->register_V[C8_REG_V2_IDX(instr)];
uint8_t byte_num = (instr & 0x000F);
uint8_t sprite_byte;
uint16_t display_index;
chip8->register_V[0xF] = 0;
for (int byte = 0; byte < byte_num; byte++) {
sprite_byte = chip8->memory[chip8->register_I + byte];
for (int bit = 0; bit < 8; bit++) {
if (((0x80 >> bit) & sprite_byte) != 0) {
display_index = ((y + byte) * chip8->display_width) + x + bit;
if (chip8->display[display_index] == 1) {
chip8->register_V[0xF] = 1;
}
chip8->display[display_index] ^= 1;
}
}
}
chip8->update_display = true;
chip8->program_counter += 2;
return;
}
case 0xE000: {
switch (instr & 0x00FF) {
case 0x9E: {
uint8_t key = chip8->register_V[C8_REG_V_IDX(instr)];
if (chip8->input_keys[key]) {
chip8->program_counter += 4;
} else {
chip8->program_counter += 2;
}
return;
}
case 0xA1: {
uint8_t key = chip8->register_V[C8_REG_V_IDX(instr)];
if (chip8->input_keys[key]) {
chip8->program_counter += 2;
} else {
chip8->program_counter += 4;
}
return;
}
default: {
break;
}
}
}
case 0xF000: {
switch (instr & 0x00FF) {
case 0x07: {
chip8->register_V[C8_REG_V_IDX(instr)] = chip8->register_delay_timer;
chip8->program_counter += 2;
return;
}
case 0x0A: {
chip8->wait_key_V_reg = C8_REG_V_IDX(instr);
chip8->program_counter += 2;
return;
}
case 0x15: {
chip8->register_delay_timer = chip8->register_V[C8_REG_V_IDX(instr)];
chip8->program_counter += 2;
return;
}
case 0x18: {
chip8->register_sound_timer = chip8->register_V[C8_REG_V_IDX(instr)];
chip8->program_counter += 2;
return;
}
case 0x1E: {
chip8->register_I += chip8->register_V[C8_REG_V_IDX(instr)];
chip8->program_counter += 2;
return;
}
case 0x29: {
chip8->register_I = (chip8->register_V[C8_REG_V_IDX(instr)] * 5);
chip8->program_counter += 2;
return;
}
case 0x33: {
uint8_t value = chip8->register_V[C8_REG_V_IDX(instr)];
chip8->memory[chip8->register_I] = value / 100;
chip8->memory[chip8->register_I + 1] = (value / 10) % 10;
chip8->memory[chip8->register_I + 2] = value % 10;
chip8->program_counter += 2;
return;
}
case 0x55: {
uint8_t v_reg_num = C8_REG_V_IDX(instr) + 1;
for (int k = 0; k < v_reg_num; k++) {
chip8->memory[chip8->register_I + k] = chip8->register_V[k];
}
chip8->program_counter += 2;
return;
}
case 0x65: {
uint8_t v_reg_num = C8_REG_V_IDX(instr) + 1;
for (int k = 0; k < v_reg_num; k++) {
chip8->register_V[k] = chip8->memory[chip8->register_I + k];
}
chip8->program_counter += 2;
return;
}
default: {
break;
}
}
}
default: {
break;
}
}
C8_LOG_ERROR("Unknown instruction %X", instr);
chip8->program_counter += 2;
}
void c8_update_timers(Chip8 *chip8)
{
if (chip8->register_delay_timer != 0) {
chip8->register_delay_timer--;
}
if (chip8->register_sound_timer != 0) {
chip8->register_sound_timer--;
}
}