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chip8.cpp
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#include "chip8.h"
void audioCallback(void *user_data, Uint8 *raw_buffer, int bytes) {
Sint16 *buffer = (Sint16*)raw_buffer;
int length = bytes / 2; // 2 bytes per sample for AUDIO_S16SYS
int &sample_nr(*(int*)user_data);
for (int i = 0; i < length; i++, sample_nr++) {
double time = (double)sample_nr / (double)SAMPLE_RATE;
buffer[i] = (Sint16)(AMPLITUDE * sin(2.0f * M_PI * 659.25f * time)); // render 600 HZ sine wave
}
}
void CHIP8::init() {
// Initialization flag
bool success = true;
// Initialize SDL
if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO) < 0) {
printf("SDL could not initialize! SDL_Error: %s\n", SDL_GetError());
success = false;
} else {
// Create window
window = SDL_CreateWindow("Chip8", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_SHOWN);
if (window == NULL) {
printf("Window could not be created! SDL_Error: %s\n", SDL_GetError());
success = false;
} else {
// Get window surface
screenSurface = SDL_GetWindowSurface(window);
}
}
// Fill the surface blue (background)
SDL_FillRect(screenSurface, NULL, 0xFF);
// Initialize pixels
for (int i = 0; i < ROWS * COLS; i++) {
pixels[i].w = pixelWidth;
pixels[i].h = pixelHeight;
int row = i / COLS;
pixels[i].x = (i - row * COLS) * pixelWidth;
pixels[i].y = row * pixelHeight;
}
updateScreen();
// Audio (beeper)
int sample_nr = 0;
SDL_AudioSpec want, have;
want.freq = SAMPLE_RATE; // number of samples per second
want.format = AUDIO_S16SYS; // sample type (here: signed short i.e. 16 bit)
want.channels = 1; // only one channel
want.samples = 2048; // buffer-size
want.callback = audioCallback; // function SDL calls periodically to refill the buffer
want.userdata = &sample_nr; // counter, keeping track of current sample number
if (SDL_OpenAudio(&want, &have) < 0)
SDL_LogError(SDL_LOG_CATEGORY_AUDIO, "Failed to open audio: %s", SDL_GetError());
// Fonts
u8 fonts[80] = {
0xF0, 0x90, 0x90, 0x90, 0xF0, // 0
0x20, 0x60, 0x20, 0x20, 0x70, // 1
0xF0, 0x10, 0xF0, 0x80, 0xF0, // 2
0xF0, 0x10, 0xF0, 0x10, 0xF0, // 3
0x90, 0x90, 0xF0, 0x10, 0x10, // 4
0xF0, 0x80, 0xF0, 0x10, 0xF0, // 5
0xF0, 0x80, 0xF0, 0x90, 0xF0, // 6
0xF0, 0x10, 0x20, 0x40, 0x40, // 7
0xF0, 0x90, 0xF0, 0x90, 0xF0, // 8
0xF0, 0x90, 0xF0, 0x10, 0xF0, // 9
0xF0, 0x90, 0xF0, 0x90, 0x90, // A
0xE0, 0x90, 0xE0, 0x90, 0xE0, // B
0xF0, 0x80, 0x80, 0x80, 0xF0, // C
0xE0, 0x90, 0x90, 0x90, 0xE0, // D
0xF0, 0x80, 0xF0, 0x80, 0xF0, // E
0xF0, 0x80, 0xF0, 0x80, 0x80 // F
};
memcpy(&M[0], &fonts, 80);
}
void CHIP8::clearScreen() {
for (int i = 0; i < ROWS * COLS; i++) {
pixels[i].status = 0;
}
updateScreen();
}
void CHIP8::updateScreen() {
for (int i = 0; i < ROWS * COLS; i++) {
SDL_FillRect(screenSurface, &pixels[i], pixels[i].status ? WHITE : BLACK);
}
}
void CHIP8::loadProgram(u8* block, u16 size) {
programSize = size;
memcpy(&M[INIT_PC], block, size);
}
void CHIP8::runProgram() {
PC = INIT_PC;
SP = 0;
DT = 0;
ST = 0;
I = 0;
// Some programs don't clear the screen!
clearScreen();
int currTick;
int prevTick = -1;
SDL_Event e;
bool quit = false;
while (!quit) {
if (SDL_PollEvent(&e)) {
if (e.type == SDL_QUIT) {
quit = true;
}
}
currTick = SDL_GetTicks();
if (currTick != prevTick) {
prevTick = currTick;
if (currTick % (1000 / freq) == 0) {
if (!tick())
break;
}
if (currTick % 16 == 0) {
// Must keep rendering pixels
SDL_UpdateWindowSurface(window);
// Delay and sound decrease at 60Hz
if (DT > 0) {
DT--;
}
if (ST > 0) {
ST--;
if (ST == 0)
SDL_PauseAudio(1); // stop playing sound
}
}
}
}
}
bool CHIP8::tick() {
if (PC > INIT_PC + programSize)
return false; // Reached end of program
u16 op = M[PC] << 8 | M[PC + 1];
if (DEBUG_MSG)
printf("inst: %x, PC: %x, time: %d\n", op, PC, SDL_GetTicks());
if (!execInst(op))
return false;
PC += 2;
return true;
}
bool CHIP8::execInst(u16 op) {
switch (op) {
case 0xE0: // Clear screen
clearScreen();
break;
case 0xEE: // Return from a subroutine
if (SP == 0) {
printf("No address to return to\n");
return false;
}
PC = stack[--SP];
break;
default:
u8 x = op >> 8 & 0xF;
u8 y = op >> 4 & 0xF;
switch(op >> 12) {
case 0x1: // Jump to location nnn
PC = (op & 0xFFF) - 2;
break;
case 0x2: // Call subroutine at nnn
if (SP >= 0xF) {
printf("Stack overflow\n");
return false;
}
stack[SP++] = PC;
PC = (op & 0xFFF) - 2;
break;
case 0x3: // Skip next instruction if Vx = kk
if (V[x] == (op & 0xFF))
PC += 2;
break;
case 0x4: // Skip next instruction if Vx != kk
if (V[x] != (op & 0xFF))
PC += 2;
break;
case 0x5: // Skip next instruction if Vx = Vy.
if (V[x] == V[y])
PC += 2;
break;
case 0x6: // Set Vx = kk
V[x] = op & 0xFF;
break;
case 0x7: // Set Vx = Vx + kk
V[x] += op & 0xFF;
break;
case 0x8:
switch (op & 0xF) {
case 0: // Set Vx = Vy
V[x] = V[y];
break;
case 1: // Set Vx = Vx OR Vy
V[x] = V[x] | V[y];
break;
case 2: // Set Vx = Vx AND Vy
V[x] = V[x] & V[y];
break;
case 3: // Set Vx = Vx XOR Vy
V[x] = V[x] ^ V[y];
break;
case 4: // Set Vx = Vx + Vy, set VF = carry
V[0xF] = V[x] + V[y] > 0xFF;
V[x] = V[x] + V[y];
break;
case 5: // Set Vx = Vx - Vy, set VF = NOT borrow
V[0xF] = V[x] > V[y];
V[x] = V[x] - V[y];
break;
case 6: // Set Vx = Vx SHR 1
V[0xF] = V[x] & 0xF;
V[x] = V[x] >> 1;
break;
case 7: // Set Vx = Vy - Vx, set VF = NOT borrow
V[0xF] = V[y] > V[x];
V[x] = V[y] - V[x];
break;
case 0xE: // Set Vx = Vx SHL 1
V[0xF] = V[x] & 0xF;
V[x] = V[x] << 1;
break;
default:
printf("Unknown OPcode: %x\n", op);
}
break;
case 0x9: // Skip next instruction if Vx != Vy
if (V[x] != V[y])
PC += 2;
break;
case 0xA: // Set I = nnn
I = op & 0xFFF;
break;
case 0xB: // Jump to location nnn + V0
PC = (op & 0xFFF) + V[0];
break;
case 0xC: // Set Vx = random byte AND kk
V[x] = (rand() % 255) & (op & 0xFF);
break;
case 0xD: { // Display n-byte sprite starting at memory location I at (Vx, Vy), set VF = collision
V[0xF] = 0;
for (u8 i = 0; i < (op & 0xF); i++) {
for (int8_t j = 7; j >= 0; j--) {
u16 pos = (V[y] + i) % ROWS * COLS + (V[x] + 7 - j) % COLS;
u8 val = (M[I + i] >> j) & 1;
if ((pixels[pos].status ^ val) != pixels[pos].status)
V[0xF] = 1;
pixels[pos].status ^= val;
}
}
if (V[0xF] != 0)
updateScreen();
break;
}
case 0xE:
switch (op & 0xFF) {
case 0x9E: // Skip next instruction if key with the value of Vx is pressed
if (SDL_GetKeyboardState(NULL)[keymap[V[x]]])
PC += 2;
break;
case 0xA1: // Skip next instruction if key with the value of Vx is not pressed.
if (!SDL_GetKeyboardState(NULL)[keymap[V[x]]])
PC += 2;
break;
default:
printf("Unknown OPcode: %x\n", op);
}
break;
case 0xF:
switch (op & 0xFF) {
case 0x7: // Set Vx = delay timer value
V[x] = DT;
break;
case 0xA: { // Wait for a key press, store the value of the key in Vx
SDL_Event e;
u8 found = 0;
while (!found) {
while (SDL_PollEvent(&e) != 0) {
if (e.type == SDL_KEYDOWN) {
for (u8 i = 0; i < 16; i++) {
if (keymap[i] == e.key.keysym.scancode) {
V[x] = i;
found = 1;
break;
}
}
}
}
}
break;
}
case 0x15: // Set delay timer = Vx
DT = V[x];
break;
case 0x18: // Set sound timer = Vx
ST = V[x];
if (ST != 0)
SDL_PauseAudio(0); // play sound
else
SDL_PauseAudio(1); // stop sound
break;
case 0x1E: // Set I = I + Vx
I = I + V[x];
break;
case 0x29: // Set I = location of sprite for digit Vx
I = V[x] * 5;
break;
case 0x33: // Store BCD representation of Vx in memory locations I, I+1, and I+2
M[I] = V[x] / 100;
M[I + 1] = (V[x] / 10) % 10;
M[I + 2] = V[x] % 10;
break;
case 0x55: // Store registers V0 through Vx in memory starting at location I
for (u8 i = 0; i <= x; i++) {
M[I + i] = V[i];
}
break;
case 0x65: // Read registers V0 through Vx from memory starting at location I
for (u8 i = 0; i <= x; i++) {
V[i] = M[I + i];
}
break;
default:
printf("Unknown OPcode: %x\n", op);
}
break;
default:
printf("Unknown OPcode: %x\n", op);
}
}
return true;
}
void CHIP8::close() {
// Destroy pixels
delete[] pixels;
// Destroy audio
SDL_CloseAudio();
// Destroy window
SDL_DestroyWindow(window);
window = NULL;
// Quit SDL subsystems
SDL_Quit();
}