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chip8.cpp
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chip8.cpp
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#include "chip8.h"
// Chip-8 Class Methods Definition
bool pressedKey = false;
unsigned short pixel, xaux, yaux;
int height;
unsigned char chip8_fontset[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
};
void chip8::initialize(){
// Clears the memory of the system
for(int i = 0; i < 4096; i++){
memory[i] = 0;
}
// Clears all registers and the stack
for(int i = 0; i < 16; i++){
v[i] = 0;
stack[i] = 0;
keyboard[i] = 0;
}
// Clears the display
for(int i = 0; i < 2048; i++){
display[i] = 0;
}
// Uploads the fontset to the Memory
for(int i = 0; i < 80; i++){
memory[i] = chip8_fontset[i];
}
opcode = 0;
pc = 0x200;
sp = 0;
I = 0;
soundTimer = 0;
delayTimer = 0;
drawFlag = 1;
}
bool chip8::loadGame(std::string game){
//printf("Loading the game....\n");
FILE *gameP = fopen(game.c_str(), "rb");
if(gameP == NULL){
//printf("ERROR! Game file not found!\n");
return false;
}
// Finds the size of the game
fseek(gameP, 0, SEEK_END);
long int gameSize = ftell(gameP);
fseek(gameP, 0, SEEK_SET);
// Reads the data from the game into the buffer
char *buffer = (char*) malloc(sizeof(char)*gameSize);
if(buffer == NULL){
return false;
}
fread(buffer, 1, gameSize, gameP);
// Writes the data on the memory
for(int i = 0; i < gameSize; i++){
memory[i + 512] = buffer[i];
//printf("Memory[%d] = %d\n", i+512,memory[i+512]);
}
fclose(gameP);
free(buffer);
return true;
}
void chip8::nextCycle(){
// Fetching the instruction
opcode = memory[pc] << 8 | memory[pc+1];
// Decoding the instruction
switch(opcode & GET_4BITS){ // Decode the instruction based on the first 4 bits
// Decodification of the 0x0 opcodes
case 0x0000:
switch(opcode & GET_8BIT_CONSTANT){
// Clears the screen.
case 0x00E0:
for(int i = 0; i < 32*64; i++){
display[i] = 0;
}
pc += 2;
drawFlag = 1;
//printf("CLS\n");
break;
// Returns from a subroutine.
case 0x00EE:
sp--;
pc = stack[sp];
pc += 2;
//printf("RET\n");
break;
}
break;
// Jumps to the address NNN
case 0x1000:
pc = (opcode & GET_ADDRESS);
//printf("JMP %d\n", opcode & GET_ADDRESS);
break;
// Calls subroutine at NNN.
case 0x2000:
stack[sp] = pc;
sp++;
pc = opcode & GET_ADDRESS;
//printf("CALL %d\n", opcode & GET_ADDRESS);
break;
// Skips the next instruction if v[X] is equal to NN
case 0x3000:
if(v[(opcode & GET_X) >> 8] == (opcode & GET_8BIT_CONSTANT))
pc += 4;
else
pc += 2;
//printf("SE V%d,%d\n", (opcode & GET_X) >> 8, opcode & GET_8BIT_CONSTANT);
break;
// Skips the next instruction if v[X] is not equal to NN
case 0x4000:
if(v[(opcode & GET_X) >> 8] != (opcode & GET_8BIT_CONSTANT))
pc += 4;
else
pc += 2;
//printf("SNE V%d,%d\n", (opcode & GET_X) >> 8, opcode & GET_8BIT_CONSTANT);
break;
// Skips the next instruction if v[X] is equal to v[Y]
case 0x5000:
if(v[(opcode & GET_X) >> 8] == v[(opcode & GET_Y) >> 4]){
pc += 4;
}
else
pc += 2;
//printf("SE V%d,V%d\n", (opcode & GET_X) >> 8, (opcode & GET_Y) >> 4);
break;
// Sets v[X] to NN
case 0x6000:
v[(opcode & GET_X) >> 8] = (opcode & GET_8BIT_CONSTANT);
pc += 2;
//printf("LD V%d,%d\n", (opcode & GET_X) >> 8, opcode & GET_8BIT_CONSTANT);
break;
// Adds NN to v[X]
case 0x7000:
v[(opcode & GET_X) >> 8] += (opcode & GET_8BIT_CONSTANT);
pc += 2;
//printf("ADD V%d,%d\n", (opcode & GET_X) >> 8, opcode & GET_8BIT_CONSTANT);
break;
// Skips the next instruction if v[X] is not equal to v[Y]
case 0x9000:
if(v[opcode & GET_X >> 8] != v[(opcode & GET_Y) >> 4]){
pc += 4;
}
else pc += 2;
//printf("SNE V%d,V%d\n", (opcode & GET_X) >> 8, (opcode & GET_Y) >> 4);
break;
case 0x8000:
switch(opcode & GET_4BIT_CONSTANT){
// Sets v[X] to v[Y]
case 0x0000:
v[(opcode & GET_X) >> 8] = v[(opcode & GET_Y) >> 4];
pc += 2;
//printf("LD V%d,V%d\n", (opcode & GET_X) >> 8, (opcode & GET_Y) >> 4);
break;
// Sets v[X] to v[X] OR v[Y]
case 0x0001:
v[(opcode & GET_X) >> 8] |= v[(opcode & GET_Y) >> 4];
pc += 2;
//printf("OR V%d,V%d\n", (opcode & GET_X) >> 8, (opcode & GET_Y) >> 4);
break;
// Sets v[X] to v[X] AND v[Y]
case 0x0002:
v[(opcode & GET_X) >> 8] &= v[(opcode & GET_Y) >> 4];
pc += 2;
//printf("AND V%d,V%d\n", (opcode & GET_X) >> 8, (opcode & GET_Y) >> 4);
break;
// Sets v[X] to v[X] XOR v[Y]
case 0x0003:
v[(opcode & GET_X) >> 8] ^= v[(opcode & GET_Y) >> 4];
pc += 2;
//printf("XOR V%d,V%d\n", (opcode & GET_X) >> 8, (opcode & GET_Y) >> 4);
break;
// Adds VY to VX. VF is set to 1 when there's a carry, and to 0 when there isn't.
case 0x0004:
if(v[(opcode & GET_Y) >> 4] > (0xFF - v[(opcode & GET_X) >> 8]))
v[0xF] = 1;
else
v[0xF] = 0;
v[(opcode & GET_X) >> 8] += v[(opcode & GET_Y) >> 4];
pc += 2;
//printf("ADD V%d,V%d\n", (opcode & GET_X) >> 8, (opcode & GET_Y) >> 4);
break;
// VY is subtracted from VX. VF is set to 0 when there's a borrow, and 1 when there isn't.
case 0x0005:
if(v[(opcode & GET_X) >> 8] > v[(opcode & GET_Y) >> 4])
v[0xF] = 1;
else
v[0xF] = 0;
v[(opcode & GET_X) >> 8] -= v[(opcode & GET_Y) >> 4];
pc += 2;
//printf("SUB V%d,V%d\n", (opcode & GET_X) >> 8, (opcode & GET_Y) >> 4);
break;
// Stores the least significant bit of VX in VF and then shifts VX to the right by 1.
case 0x0006:
if((v[(opcode & GET_X) >> 8] & 0x01) == 0x01)
v[0xF] = 1;
else
v[0xF] = 0;
pc += 2;
v[(opcode & GET_X) >> 8] = v[(opcode & GET_X) >> 8]/2;
//printf("SHR V%d,V%d\n", (opcode & GET_X) >> 8, (opcode & GET_Y) >> 4);
break;
// Sets VX to VY minus VX. VF is set to 0 when there's a borrow, and 1 when there isn't.
case 0x0007:
if(v[(opcode & GET_Y) >> 4] > v[(opcode & GET_X) >> 8])
v[0xF] = 1;
else
v[0xF] = 0;
v[(opcode & GET_X) >> 8] = v[(opcode & GET_Y) >> 4] - v[(opcode & GET_X) >> 8];
pc += 2;
//printf("SUBN V%d,V%d\n", (opcode & GET_X) >> 8, (opcode & GET_Y) >> 4);
break;
// Stores the most significant bit of VX in VF and then shifts VX to the left by 1.
case 0x000E:
if((v[(opcode & GET_X) >> 8] & 0x80) == 0x80)
v[0xF] = 1;
else
v[0xF] = 0;
pc += 2;
v[(opcode & GET_X) >> 8] = v[(opcode & GET_X) >> 8]*2;
//printf("SHL V%d,V%d\n", (opcode & GET_X) >> 8, (opcode & GET_Y) >> 4);
break;
}
break;
// Sets the I address to NNN
case 0xA000:
I = opcode & GET_ADDRESS;
pc += 2;
//printf("LD I, %d\n", opcode & GET_ADDRESS);
break;
// Jumps to the address V0 + NNN
case 0xB000:
pc = (opcode & GET_ADDRESS) + v[0];
//printf("JP V0,%d\n", opcode & GET_ADDRESS);
break;
// Sets VX to the result of a bitwise and operation on a random number (Typically: 0 to 255) and NN.
case 0xC000:
v[opcode & GET_X >> 8] = (rand() % 255) & (opcode & GET_8BIT_CONSTANT);
pc += 2;
//printf("RND V%d,%d\n", (opcode & GET_X) >> 8, opcode & GET_8BIT_CONSTANT);
break;
// Draws a sprite at (vx,vy) with size height of N pixels
case 0xD000:
xaux = v[(opcode & GET_X) >> 8];
yaux = v[(opcode & GET_Y) >> 4];
height = opcode & GET_4BIT_CONSTANT;
v[0xF] = 0; // Resets the VF
for(int y = 0; y < height; y++){ // Passes through all lines of the sprite
pixel = memory[I + y]; // Fetches the pixel value on the memory
for(int x = 0; x < 8; x++){ // Passes through all 8 columns of the sprite, in each line
if((pixel & (0x80 >> x)) != 0){
if(display[(xaux + x + ((yaux + y)*64))] == 1)
v[0xF] = 1; // Registers the collision
display[(xaux + x + ((yaux + y)*64))] ^= 1;
}
}
}
drawFlag = true;
pc += 2;
//printf("DRW V%d,V%d,%d\n", (opcode & GET_X) >> 8, (opcode & GET_Y) >> 4, opcode & GET_4BIT_CONSTANT);
break;
case 0xE000:
switch(opcode & GET_4BIT_CONSTANT){
// Skips the next instruction if the key stored in VX is pressed.
case 0x000E:
//printf("SKP V%d\n", (opcode & GET_X) >> 8);
if(keyboard[v[(opcode & GET_X) >> 8]] != 0)
pc += 4;
else
pc += 2;
break;
// Skips the next instruction if the key stored in VX isn't pressed.
case 0x0001:
//printf("SKNP V%d\n", (opcode & GET_X) >> 8);
if(keyboard[v[(opcode & GET_X) >> 8]] == 0)
pc += 4;
else
pc += 2;
break;
}
break;
case 0xF000:
switch(opcode & GET_8BIT_CONSTANT){
// Sets VX to the value of the delay timer.
case 0x0007:
v[(opcode & GET_X) >> 8] = delayTimer;
pc += 2;
//printf("LD V%d, DT\n", (opcode & GET_X) >> 8);
break;
// A key press is awaited, and then stored in VX
case 0x000A:
//printf("KEYWAIT V%d, K\n", (opcode & GET_X) >> 8);
pressedKey = false;
while(!pressedKey){
for(int i = 0; i < 16; i++){
if(keyboard[i] != 0){
v[(opcode & GET_X) >> 8] = i;
pressedKey = true;
break;
}
}
}
pc += 2;
break;
// Sets the delay timer to the value of v[X]
case 0x0015:
//printf("LD DT, V%d\n", (opcode & GET_X) >> 8);
delayTimer = v[(opcode & GET_X) >> 8];
pc += 2;
break;
// Sets the sound timer to the value of v[X]
case 0x0018:
//printf("LD ST, V%d\n", (opcode & GET_X) >> 8);
soundTimer = v[(opcode & GET_X) >> 8];
pc += 2;
break;
// Adds v[X] to I
case 0x001E:
//printf("ADD I, V%d\n", (opcode & GET_X) >> 8);
if((I + v[(opcode & GET_X) >> 8]) > 0xFFFF)
v[0xF] = 1;
else
v[0xF] = 0;
I += v[(opcode & GET_X) >> 8];
pc += 2;
break;
// Sets I to the location of the sprite for the character in VX.
case 0x0029:
//printf("LD F, V%d\n", (opcode & GET_X) >> 8);
I = v[(opcode & GET_X) >> 8] * 0x5;
pc += 2;
break;
// Stores the Binary-coded decimal representation of VX at the addresses I, I plus 1, and I plus 2
// Implementation by TJA
case 0x0033:
//printf("LD B, V%d\n", (opcode & GET_X) >> 8);
memory[I] = v[(opcode & 0x0F00) >> 8] / 100;
memory[I + 1] = (v[(opcode & 0x0F00) >> 8] / 10) % 10;
memory[I + 2] = (v[(opcode & 0x0F00) >> 8] % 100) % 10;
pc += 2;
break;
//Stores V0 to VX (including VX) in memory starting at address I.
case 0x0055:
//printf("LD [I], V%d\n", (opcode & GET_X) >> 8);
for(int i = 0; i <= ((opcode & GET_X) >> 8); i++){
memory[I+i] = v[i];
}
I += ((opcode & GET_X) >> 8) + 1;
pc += 2;
break;
// Fills V0 to VX (including VX) with values from memory starting at address I.
case 0x0065:
//printf("I = %d\n", I);
//printf("LD V%d, [I]\n", (opcode & GET_X) >> 8);
for(int i = 0; i <= ((opcode & GET_X) >> 8) ; i++){
v[i] = memory[I+i];
}
I += ((opcode & GET_X) >> 8) + 1;
pc += 2;
break;
}
break;
default:
//printf("ERROR! Opcode not known!\n");
break;
}
// Decrement the timers if they are greater than zero
if(delayTimer > 0)
delayTimer--;
if(soundTimer > 0)
if(soundTimer == 1){
playSound = true;
//printf("BEEP\n");
}
soundTimer--;
}