feat: initial version
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12 changed files with 798 additions and 0 deletions
257
srcs/cpu.c
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257
srcs/cpu.c
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#include "input.h"
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#include "cpu.h"
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#include "font.h"
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#include <stdio.h>
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#include <stdint.h>
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#define OPCODE_SIZE 2
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uint16_t cpu_fetch(t_chip8 *emu)
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{
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// Check if there is enough space in memory to fetch a 2-byte opcode
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if (emu->pc + 1 >= MEMORY_SIZE)
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{
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printf("Error, program counter out of bounds! (pc = 0x%04X)\n", emu->pc);
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graphics_cleanup(&emu->display);
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emu->running = 0;
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return (1);
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}
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uint16_t opcode = (emu->memory.memory[emu->pc] << 8) | emu->memory.memory[emu->pc + 1];
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return opcode;
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}
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t_instruction cpu_decode(uint16_t opcode)
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{
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t_instruction instruction;
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instruction.opcode = opcode;
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instruction.type = (opcode & 0xF000) >> 12;
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instruction.x = (opcode & 0x0F00) >> 8;
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instruction.y = (opcode & 0x00F0) >> 4;
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instruction.n = opcode & 0x000F;
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instruction.nn = opcode & 0x00FF;
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instruction.nnn = opcode & 0x0FFF;
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return instruction;
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}
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void cpu_execute(t_chip8 *emu, t_instruction instruction)
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{
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uint8_t x = instruction.x;
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uint8_t y = instruction.y;
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uint8_t n = instruction.n;
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uint8_t nn = instruction.nn;
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uint16_t nnn = instruction.nnn;
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switch (instruction.type)
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{
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// 0x0NNN: SYS addr (ignored, do nothing)
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case 0x0:
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// 0x00E0: CLS (Clear screen)
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if (instruction.opcode == 0x00E0)
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memory_clear_screen(&emu->memory);
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// 0x00EE: RET (Return from subroutine)
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else if (instruction.opcode == 0x00EE) {
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if (emu->sp == 0)
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{
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printf("Stack underflow on RET!\n");
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emu->running = 0;
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return;
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}
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emu->pc = emu->stack[--emu->sp];
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}
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break;
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// 0x1NNN: JP addr (Jump to address NNN)
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case 0x1:
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emu->pc = nnn;
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return; // Do not increment PC after jump
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// 0x2NNN: CALL addr (Call subroutine at NNN)
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case 0x2:
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if (emu->sp >= 16)
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{
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printf("Stack overflow!\n");
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emu->running = 0;
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return;
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}
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emu->stack[emu->sp++] = emu->pc;
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emu->pc = nnn;
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return; // Do not increment PC after call
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// 0x3XNN: SE Vx, byte (Skip if Vx == NN)
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case 0x3:
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if (emu->v[x] == nn)
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emu->pc += OPCODE_SIZE;
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break;
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// 0x4XNN: SNE Vx, byte (Skip if Vx != NN)
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case 0x4:
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if (emu->v[x] != nn)
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emu->pc += OPCODE_SIZE;
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break;
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// 0x5XY0: SE Vx, Vy (Skip if Vx == Vy)
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case 0x5:
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if (n == 0 && emu->v[x] == emu->v[y])
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emu->pc += OPCODE_SIZE;
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break;
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// 0x6XNN: LD Vx, byte (Load NN into Vx)
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case 0x6:
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emu->v[x] = nn;
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break;
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// 0x7XNN: ADD Vx, byte (Add NN to Vx)
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case 0x7:
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emu->v[x] += nn;
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break;
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// 0x8XYN: Arithmetic opcodes (switch on last nibble, 'n')
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case 0x8:
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switch (n)
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{
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// 0x8XY0: LD Vx, Vy (Set Vx = Vy)
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case 0x0:
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emu->v[x] = emu->v[y];
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break;
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// 0x8XY1: OR Vx, Vy (Set Vx = Vx OR Vy)
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case 0x1:
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emu->v[x] |= emu->v[y];
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break;
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// 0x8XY2: AND Vx, Vy (Set Vx = Vx AND Vy)
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case 0x2:
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emu->v[x] &= emu->v[y];
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break;
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// 0x8XY3: XOR Vx, Vy (Set Vx = Vx XOR Vy)
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case 0x3:
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emu->v[x] ^= emu->v[y];
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break;
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// 0x8XY4: ADD Vx, Vy (Set Vx = Vx + Vy, set VF = carry)
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case 0x4:
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emu->v[0xF] = (emu->v[x] + emu->v[y]) > 0xFF;
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emu->v[x] += emu->v[y];
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break;
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// 0x8XY5: SUB Vx, Vy (Set Vx = Vx - Vy, set VF = NOT borrow)
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case 0x5:
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emu->v[0xF] = emu->v[x] >= emu->v[y];
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emu->v[x] -= emu->v[y];
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break;
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// 0x8XY6: SHR Vx, Vy (Set Vx = Vx >> 1, set VF = LSB before shift)
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case 0x6:
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emu->v[0xF] = emu->v[x] & 1;
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emu->v[x] >>= 1;
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break;
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// 0x8XY7: SUBN Vx, Vy (Set Vx = Vy - Vx, set VF = NOT borrow)
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case 0x7:
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emu->v[0xF] = emu->v[y] >= emu->v[x];
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emu->v[x] = emu->v[y] - emu->v[x];
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break;
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// 0x8XYE: SHL Vx, Vy (Set Vx = Vx << 1, set VF = MSB before shift)
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case 0xE:
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emu->v[0xF] = (emu->v[x] >> 7) & 1;
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emu->v[x] <<= 1;
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break;
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default:
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printf("Unknown arithmetic opcode: 0x%04X\n", instruction.opcode);
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break;
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}
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break;
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// 0x9XY0: SNE Vx, Vy (Skip if Vx != Vy)
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case 0x9:
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if (n == 0 && emu->v[x] != emu->v[y])
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emu->pc += OPCODE_SIZE;
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break;
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// 0x0ANNN: LD I, addr (Set I = NNN)
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case 0xA:
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emu->i = nnn;
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break;
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// 0xBNNN: JP V0, addr (Jump to NNN + V0)
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case 0xB:
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emu->pc = nnn + emu->v[0];
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return; // Do not increment PC after jump
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// 0xCXNN: RND Vx, byte (Set Vx = random byte AND NN)
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case 0xC:
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emu->v[x] = (rand() & 0xFF) & nn;
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break;
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// 0xDXYN: DRW Vx, Vy, nibble (Draw sprite at (Vx, Vy), N rows)
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// N=0 means 16 rows (wrapping)
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case 0xD:
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graphics_draw_sprite(emu, emu->v[x] % 64, emu->v[y] % 32, n);
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break;
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// 0xEX9E: SKP Vx (Skip if key Vx is pressed)
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// 0xEXA1: SKNP Vx (Skip if key Vx is not pressed)
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case 0xE:
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if (nn == 0x9E)
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{
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if (emu->keyboard.keyboard[emu->v[x] & 0xF])
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emu->pc += OPCODE_SIZE;
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}
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else if (nn == 0xA1)
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{
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if (!emu->keyboard.keyboard[emu->v[x] & 0xF])
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emu->pc += OPCODE_SIZE;
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}
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break;
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// 0xFXNN: Various instructions (switch on NN)
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case 0xF:
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switch (nn)
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{
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// 0xFX07: LD Vx, DT (Set Vx = delay timer)
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case 0x07:
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emu->v[x] = emu->delay_timer;
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break;
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// 0xFX0A: LD Vx, K (Wait for key press, store in Vx)
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case 0x0A:
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emu->keyboard.waiting_for_key = 1;
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emu->keyboard.key_register = x;
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break;
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// 0xFX15: LD DT, Vx (Set delay timer = Vx)
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case 0x15:
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emu->delay_timer = emu->v[x];
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break;
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// 0xFX18: LD ST, Vx (Set sound timer = Vx)
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case 0x18:
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emu->sound_timer = emu->v[x];
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break;
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// 0xFX1E: ADD I, Vx (Set I = I + Vx)
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case 0x1E:
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emu->i += emu->v[x];
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break;
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// 0xFX29: LD F, Vx (Set I = font sprite address for character in Vx)
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case 0x29:
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// emu->i = 0x50 + 5 * (emu->v[x] & 0xF);
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emu->i = FONTSET_START + 5 * (emu->v[x] & 0xF);
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break;
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// 0xFX33: LD B, Vx (Store BCD representation of Vx at I, I+1, I+2)
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case 0x33:
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emu->memory.memory[emu->i] = (emu->v[x] / 100) % 10;
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emu->memory.memory[emu->i + 1] = (emu->v[x] / 10) % 10;
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emu->memory.memory[emu->i + 2] = emu->v[x] % 10;
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break;
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// 0xFX55: LD [I], Vx (Store V0-Vx in memory starting at I)
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case 0x55:
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for (int i = 0; i <= x; i++)
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emu->memory.memory[emu->i + i] = emu->v[i];
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break;
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// 0xFX65: LD Vx, [I] (Load V0-Vx from memory starting at I)
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case 0x65:
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for (int i = 0; i <= x; i++)
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emu->v[i] = emu->memory.memory[emu->i + i];
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break;
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default:
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printf("Unknown 0xF opcode: 0x%04X\n", instruction.opcode);
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break;
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}
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break;
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}
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emu->pc += OPCODE_SIZE;
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}
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