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chip8.c
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chip8.c
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#include "chip8.h"
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
unsigned char 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 init(struct Chip8* chip8) {
chip8->opcode = 0;
chip8->I = 0;
// 0x200-0xFFF - Program ROM and work RAM
chip8->pc = 0x200;
chip8->sp = 0;
//clear mem, registers, display, stack
for (int i = 0; i < 4096; ++i)
{
chip8->memory[i] = 0;
}
for (int i = 0; i < 16; ++i)
{
chip8->V[i] = 0;
}
for (int i = 0; i < 2048; ++i)
{
chip8->graphic[i] = 0;
}
chip8->updateScreen = true;
for (int i = 0; i < 16; ++i)
{
chip8->stack[i] = 0;
}
// reset timers
chip8->delay_timer = 0;
chip8->sound_timer = 0;
// fontset loaded to 0x50
for (int i = 0; i < 80; ++i)
{
chip8->memory[i] = fontset[i];
}
srand(time(NULL));
}
void cycle(struct Chip8* chip8) {
// fetch
chip8->opcode = ((chip8->memory[chip8->pc] << 8) | chip8->memory[chip8->pc + 1]) & 0xFFFF;
// printf("\nnew cycle\n");
// printf("0x%04X\n", chip8->pc);
// printf("0x%04X\n", chip8->memory[chip8->pc]);
// printf("0x%04X\n", chip8->opcode);
// decode/execute
switch(chip8->opcode & 0xF000) {
case 0x0000:
switch(chip8->opcode & 0xF) {
// 00E0 clears the screen
case 0x0:
for (int i = 0; i < 2048; ++i)
{
chip8->graphic[i] = 0x0;
}
chip8->updateScreen = true;
chip8->pc += 2;
break;
// 00EE returns from a subroutine
case 0xE:
chip8->pc = chip8->stack[--chip8->sp];
chip8->pc += 2;
break;
default:
printf("Not opcode %X\n", chip8->opcode);
}
break;
// 1NNN jumps to address NNN
case 0x1000:
chip8->pc = chip8->opcode & 0xFFF;
break;
// 2NNN calls subroutine at NNN
case 0x2000:
chip8->stack[chip8->sp++] = chip8->pc;
chip8->pc = chip8->opcode & 0xFFF;
break;
// 3XNN skips the next instructino if VX equals NN
case 0x3000:
if (chip8->V[(chip8->opcode & 0xF00) >> 8] == (chip8->opcode & 0xFF)) {
chip8->pc += 4;
} else {
chip8->pc += 2;
}
break;
// 4XNN Skips the next instruction if VX doesn't equal NN
case 0x4000:
if (chip8->V[(chip8->opcode & 0xF00) >> 8] != (chip8->opcode & 0xFF)) {
chip8->pc += 4;
} else {
chip8->pc += 2;
}
break;
// 5XY0 Skips the next instruction if VX equals VY.
case 0x5000:
if (chip8->V[(chip8->opcode & 0xF00) >> 8] == chip8->V[(chip8->opcode & 0xF0) >> 4]) {
chip8->pc += 4;
} else {
chip8->pc += 2;
}
break;
// 6XNN sets VX to NN
case 0x6000:
chip8->V[(chip8->opcode & 0xF00) >> 8] = chip8->opcode & 0xFF;
chip8->pc += 2;
break;
// 7XNN adds NN to VX
case 0x7000:
chip8->V[(chip8->opcode & 0xF00) >> 8] += chip8->opcode & 0xFF;
chip8->pc += 2;
break;
case 0x8000:
switch(chip8->opcode & 0xF) {
// 8XY0 sets VX to the value of VY
case 0x0:
chip8->V[(chip8->opcode & 0xF00) >> 8] = chip8->V[(chip8->opcode & 0xF0) >> 4];
chip8->pc += 2;
break;
// 8XY1 sets VX to VX or VY
case 0x1:
chip8->V[(chip8->opcode & 0xF00) >> 8] |= chip8->V[(chip8->opcode & 0xF0) >> 4];
chip8->pc += 2;
break;
// 8XY2 sets VX to VX and VY
case 0x2:
chip8->V[(chip8->opcode & 0xF00) >> 8] &= chip8->V[(chip8->opcode & 0xF0) >> 4];
chip8->pc += 2;
break;
// 8XY3 sets VX to VX xor VY
case 0x3:
chip8->V[(chip8->opcode & 0xF00) >> 8] ^= chip8->V[(chip8->opcode & 0xF0) >> 4];
chip8->pc += 2;
break;
// 8XY4 Adds VY to VX. VF is set to 1 when there's a carry, and to 0 when there isn't.
case 0x4:
if ((0xFF - chip8->V[(chip8->opcode & 0xF00) >> 8]) < chip8->V[(chip8->opcode & 0xF0) >> 4]) {
chip8->V[0xF] = 1;
} else {
chip8->V[0xF] = 0;
}
chip8->V[(chip8->opcode & 0xF00) >> 8] += chip8->V[(chip8->opcode & 0xF0) >> 4];
chip8->pc += 2;
break;
// 8XY5 VY is subtracted from VX. VF is set to 0 when there's a borrow, and 1 when there isn't.
case 0x5:
if (chip8->V[(chip8->opcode & 0xF00) >> 8] < chip8->V[(chip8->opcode & 0xF0) >> 4]) {
chip8->V[0xF] = 0;
} else {
chip8->V[0xF] = 1;
}
chip8->V[(chip8->opcode & 0xF00) >> 8] -= chip8->V[(chip8->opcode & 0xF0) >> 4];
chip8->pc += 2;
break;
// 8XY6 Shifts VX right by one. VF is set to the value of the least significant bit of VX before the shift.
case 0x6:
chip8->V[(0xF)] = chip8->V[(chip8->opcode & 0xF00) >> 8] & 0x1;
chip8->V[(chip8->opcode & 0xF00) >> 8] >>= 1;
chip8->pc += 2;
break;
// 8XY7 Sets VX to VY minus VX. VF is set to 0 when there's a borrow, and 1 when there isn't.
case 0x7:
if (chip8->V[(chip8->opcode & 0xF00) >> 8] > chip8->V[(chip8->opcode & 0xF0) >> 4]) {
chip8->V[0xF] = 0;
} else {
chip8->V[0xF] = 1;
}
chip8->V[(chip8->opcode & 0xF00) >> 8] = chip8->V[(chip8->opcode & 0xF0) >> 4] - chip8->V[(chip8->opcode & 0xF00) >> 8];
chip8->pc += 2;
break;
// 8XYE Shifts VX left by one. VF is set to the value of the most significant bit of VX before the shift
case 0xE:
chip8->V[(0xF)] = (chip8->V[(chip8->opcode & 0xF00) >> 8] >> 7) & 0x1;
chip8->V[(chip8->opcode & 0xF00) >> 8] <<= 1;
chip8->pc += 2;
break;
default:
printf("Not opcode %X\n", chip8->opcode);
}
break;
// 9XY0 Skips the next instruction if VX doesn't equal VY
case 0x9000:
if (chip8->V[(chip8->opcode & 0xF00) >> 8] != chip8->V[(chip8->opcode & 0xF0) >> 4]) {
chip8->pc += 4;
}
else {
chip8->pc += 2;
}
break;
// ANNN Sets I to the address NNN
case 0xA000:
chip8->I = chip8->opcode & 0xFFF;
chip8->pc += 2;
break;
// BNNN jumps to the address NNN plus V0
case 0xB000:
chip8->pc = (chip8->opcode & 0xFFF) + chip8->V[0];
break;
// CXNN Sets VX to the result of a bitwise and operation on a random number (Typically: 0 to 255) and NN.
case 0xC000:
chip8->V[(chip8->opcode & 0xF00) >> 8] = (chip8->opcode & 0xFF) & (rand() % 0xFF);
chip8->pc += 2;
break;
// DXYN Draws a sprite at coordinate (VX, VY) that has a width of 8 pixels and a height of N pixels.
// Each row of 8 pixels is read as bit-coded starting from memory location I; I value doesn’t change after the execution of this instruction.
// As described above, VF is set to 1 if any screen pixels are flipped from set to unset when the sprite is drawn, and to 0 if that doesn’t happen
case 0xD000:
{
unsigned short x = chip8->V[(chip8->opcode & 0xF00) >> 8];
unsigned short y = chip8->V[(chip8->opcode & 0xF0) >> 4];
unsigned short width = 8;
unsigned short height = chip8->opcode & 0xF;
unsigned short pixel;
for (int i = 0; i < height; ++i)
{
pixel = chip8->memory[chip8->I + i];
for (int j = 0; j < width; ++j)
{
if ((pixel & (0x80 >> j)) != 0) {
if (chip8->graphic[x + j + ((y + i) * 64)] == 1) {
chip8->V[0xF] = 1;
}
chip8->graphic[x + j + ((y + i) * 64)] ^= 1;
}
}
}
chip8->updateScreen = true;
chip8->pc += 2;
}
break;
case 0xE000:
switch(chip8->opcode & 0xFF) {
// EX9E Skips the next instruction if the key stored in VX is pressed
case 0x9E:
if (chip8->key[chip8->V[(chip8->opcode & 0xF00) >> 8]] != 0) {
chip8->pc += 4;
} else {
chip8->pc += 2;
}
break;
// EXA1 Skips the next instruction if the key stored in VX isn't pressed.
case 0XA1:
if (chip8->key[chip8->V[(chip8->opcode & 0xF00) >> 8]] == 0) {
chip8->pc += 4;
} else {
chip8->pc += 2;
}
break;
default:
printf("Not opcode %X\n", chip8->opcode);
}
break;
case 0xF000:
switch(chip8->opcode & 0xFF) {
// FX07 Sets VX to the value of the delay timer.
case 0x07:
chip8->V[(chip8->opcode & 0xF00) >> 8] = chip8->delay_timer;
chip8->pc += 2;
break;
// FX0A A key press is awaited, and then stored in VX. (Blocking Operation. All instruction halted until next key event)
case 0x0A:
{
bool press = false;
for (int i = 0; i < 16; ++i)
{
if(chip8->key[i] != 0) {
chip8->V[(chip8->opcode & 0xF00) >> 8] = i;
press = true;
}
}
if (!press) {
return;
}
chip8->pc += 2;
}
break;
// FX15 Sets the delay timer to VX.
case 0x15:
chip8->delay_timer = chip8->V[(chip8->opcode & 0xF00) >> 8];
chip8->pc += 2;
break;
// FX18 Sets the sound timer to VX.
case 0x18:
chip8->sound_timer = chip8->V[(chip8->opcode & 0xF00) >> 8];
chip8->pc += 2;
break;
// FX1E Adds VX to I
case 0x1E:
if ((chip8->I + chip8->V[(chip8->opcode & 0xF00) >> 8]) > 0xFFF) {
chip8->V[0xF] = 1;
} else {
chip8->V[0xF] = 0;
}
chip8->I += chip8->V[(chip8->opcode & 0xF00) >> 8];
chip8->pc += 2;
break;
// FX29 Sets I to the location of the sprite for the character in VX. Characters 0-F (in hexadecimal) are represented by a 4x5 font.
case 0x29:
chip8->I = chip8->V[(chip8->opcode & 0xF00) >> 8] * 0x5;
chip8->pc += 2;
break;
// FX33 Stores the binary-coded decimal representation of VX, with the most significant of three digits at the address in I,
// the middle digit at I plus 1, and the least significant digit at I plus 2. (In other words, take the decimal representation of VX,
// place the hundreds digit in memory at location in I, the tens digit at location I+1, and the ones digit at location I+2.)
case 0x33:
chip8->memory[chip8->I] = chip8->V[(chip8->opcode & 0xF00) >> 8] / 100;
chip8->memory[chip8->I + 1] = (chip8->V[(chip8->opcode & 0xF00) >> 8] / 10) % 10;
chip8->memory[chip8->I + 2] = (chip8->V[(chip8->opcode & 0xF00) >> 8] % 100) % 10;
chip8->pc += 2;
break;
// FX55 Stores V0 to VX (including VX) in memory starting at address I. I is increased by 1 for each value written.
case 0x55:
for (int i = 0; i < ((chip8->opcode & 0xF00) >> 8); ++i)
{
chip8->memory[chip8->I + i] = chip8->V[i];
}
chip8->I += ((chip8->opcode & 0xF00) >> 8) + 1;
chip8->pc += 2;
break;
// FX65 Fills V0 to VX (including VX) with values from memory starting at address I. I is increased by 1 for each value written.
case 0x65:
for (int i = 0; i < ((chip8->opcode & 0xF00) >> 8); ++i)
{
chip8->V[i] = chip8->memory[chip8->I + i];
}
chip8->I += ((chip8->opcode & 0xF00) >> 8) + 1;
chip8->pc += 2;
break;
default:
printf("Not opcode %X\n", chip8->opcode);
}
break;
default:
printf("Not opcode %X\n", chip8->opcode);
}
// update timers
if (chip8->delay_timer > 0) {
chip8->delay_timer--;
}
if (chip8->sound_timer > 0) {
chip8->sound_timer--;
}
}
bool load(const char* filename, struct Chip8* chip8) {
init(chip8);
printf("fopen %s\n", filename);
FILE* fp = fopen(filename, "rb");
if (fp == NULL) {
fputs("file null\n", stderr);
return false;
}
// get size of file
// seek to end of file then asks for position
fseek(fp, 0L, SEEK_END);
long sz = ftell(fp);
// go back to the beginning
rewind(fp);
// malloc for file size
char* buffer = malloc(sizeof(char) * sz);
// file into buffer
size_t copied_file;
if (buffer != NULL) {
fread(buffer, 1, sz, fp);
} else {
fputs("buffer null\n", stderr);
return false;
}
// make sure filesize is < space for program (4096 - 512)
if (sz < 3584) {
for (int i = 0; i < sz; ++i)
{
chip8->memory[512 + i] = buffer[i];
}
} else {
printf("filesize too big for chip 8\n");
}
fclose(fp);
free(buffer);
return true;
}