/*
* Copyright (C) 2025 dwlr <dweller@cabin.digital>
*
* BSD 3-Clause License (BSD-3-Clause)
* See LICENSE for details
*/
#define C8_RESET_VECTOR 0x200
#define C8_CYCLES_PER_FRAME 20
static const u8 fnt[] =
{
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 */
};
typedef struct
{
u16 pc;
u8 sp;
u16 i;
u16 prevkeys;
u16 keys;
u64 cycles;
/* timers: */
u8 dt; /* - delay */
u8 st; /* - sound */
bool running;
union
{
struct
{
u8 v[16];
u64 disp[32];
u8 font[sizeof(fnt)];
u16 stack[16];
} sys;
u8 ram[4*KB];
} mem;
} chip8;
#define V mem.sys.v
#define STACK mem.sys.stack
#define DISPLAY mem.sys.disp
#define FONT mem.sys.font
#define RAM mem.ram
typedef enum
{
C8_ILL,
/* Onnn = 0,1,2,A,B */
/* 00E0 - CLS */ C8_CLS,
/* 00EE - RET */ C8_RET,
/* 0nnn - SYS addr */ C8_SYS,
/* 1nnn - JP addr */ C8_JP,
/* 2nnn - CALL addr */ C8_CALL,
/* Annn - LD I, addr */ C8_LDI,
/* Bnnn - JP V0, addr */ C8_JPV,
/* Oxkk = 3,4,6,7,C,E,F */
/* 3xkk - SE Vx, byte */ C8_SEB,
/* 4xkk - SNE Vx, byte */ C8_SNEB,
/* 6xkk - LD Vx, byte */ C8_LD,
/* 7xkk - ADD Vx, byte */ C8_ADDB,
/* Cxkk - RND Vx, byte */ C8_RND,
/* Ex9E - SKP Vx */ C8_SKP,
/* ExA1 - SKNP Vx */ C8_SKNP,
/* Fx07 - LD Vx, DT */ C8_MVDT,
/* Fx0A - LD Vx, K */ C8_LDK,
/* Fx15 - LD DT, Vx */ C8_LDDT,
/* Fx18 - LD ST, Vx */ C8_LDST,
/* Fx1E - ADD I, Vx */ C8_ADDI,
/* Fx29 - LD F, Vx */ C8_HEX,
/* Fx33 - LD B, Vx */ C8_BCD,
/* Fx55 - LD [I], Vx */ C8_SAVE,
/* Fx65 - LD Vx, [I] */ C8_RESTORE,
/* Oxyn = 5,8,9,D */
/* 5xy0 - SE Vx, Vy */ C8_SE,
/* 8xy0 - LD Vx, Vy */ C8_MOVE,
/* 8xy1 - OR Vx, Vy */ C8_OR,
/* 8xy2 - AND Vx, Vy */ C8_AND,
/* 8xy3 - XOR Vx, Vy */ C8_XOR,
/* 8xy4 - ADD Vx, Vy */ C8_ADD,
/* 8xy5 - SUB Vx, Vy */ C8_SUB,
/* 8xy6 - SHR Vx {, Vy} */ C8_SHR,
/* 8xy7 - SUBN Vx, Vy */ C8_SUBN,
/* 8xyE - SHL Vx {, Vy} */ C8_SHL,
/* 9xy0 - SNE Vx, Vy */ C8_SNE,
/* Dxyn - DRW Vx, Vy, nibble */ C8_DRW,
C8_OP_CNT
} chip8_op;
void c8_reset(chip8* c8)
{
assert(c8);
assert(sizeof(c8->mem) > sizeof(fnt));
assert(sizeof(c8->mem) >= 4*KB);
memcpy(c8->FONT, fnt, sizeof(fnt));
c8->pc = C8_RESET_VECTOR;
c8->running = true;
}
void c8_dump_state(chip8* c8, bool stack)
{
int i = 0;
for(i = 0; i < (int)sizeof(c8->V); i += 4)
{
printf(" V%x: %02X (%3d) ", i+0, c8->V[i+0], c8->V[i+0]);
printf("V%x: %02X (%3d) ", i+1, c8->V[i+1], c8->V[i+1]);
printf("V%x: %02X (%3d) ", i+2, c8->V[i+2], c8->V[i+2]);
printf("V%x: %02X (%3d)\n", i+3, c8->V[i+3], c8->V[i+3]);
}
printf(" I:%04X SP: %02X DT: %02X ST: %02X CYCLES: %llu, KEYS: %X\n",
c8->i, c8->sp, c8->dt, c8->st, c8->cycles, c8->keys);
if(stack)
{
printf("stack:\n");
for(i = 0; i < (int)sizeof(c8->STACK); i += 2)
{
printf(" %-2d: %04X ", i+0, c8->STACK[i+0]);
printf("%-2d: %04X\n", i+1, c8->STACK[i+1]);
}
}
}
#define c8_decode_generate(name) \
void c8_##name(u8* code, u16 offset, void* usrdat) \
{ \
u16 word, instr, nnn; \
u8 o, x, y, n, kk; \
\
(void)usrdat; \
\
word = *(u16*)(code + offset); \
instr = be16toh(word); \
o = (instr & 0xF000) >> 12; \
nnn = (instr & 0x0FFF); \
x = (instr & 0x0F00) >> 8; \
y = (instr & 0x00F0) >> 4; \
n = (instr & 0x000F); \
kk = (instr & 0x00FF); \
\
(void)o; \
(void)nnn; \
(void)x; \
(void)y; \
(void)n; \
(void)kk; \
\
X_C8_PRELUDE; \
\
if(o == 0 && nnn == 0x0E0) X_C8_CLS; \
else if(o == 0 && nnn == 0x0EE) X_C8_RET; \
else if(o == 0) X_C8_SYS; \
else if(o == 1) X_C8_JP; \
else if(o == 2) X_C8_CALL; \
else if(o == 0xA) X_C8_LDI; \
else if(o == 0xB) X_C8_JPV; \
else if(o == 3) X_C8_SEB; \
else if(o == 4) X_C8_SNEB; \
else if(o == 6) X_C8_LD; \
else if(o == 7) X_C8_ADDB; \
else if(o == 0xC) X_C8_RND; \
else if(o == 0xE && kk == 0x9E) X_C8_SKP; \
else if(o == 0xE && kk == 0xA1) X_C8_SKNP; \
else if(o == 0xF && kk == 0x07) X_C8_MVDT; \
else if(o == 0xF && kk == 0x0A) X_C8_LDK; \
else if(o == 0xF && kk == 0x15) X_C8_LDDT; \
else if(o == 0xF && kk == 0x18) X_C8_LDST; \
else if(o == 0xF && kk == 0x1E) X_C8_ADDI; \
else if(o == 0xF && kk == 0x29) X_C8_HEX; \
else if(o == 0xF && kk == 0x33) X_C8_BCD; \
else if(o == 0xF && kk == 0x55) X_C8_SAVE; \
else if(o == 0xF && kk == 0x65) X_C8_RESTORE; \
else if(o == 5 && n == 0) X_C8_SE; \
else if(o == 8 && n == 0) X_C8_MOVE; \
else if(o == 8 && n == 1) X_C8_OR; \
else if(o == 8 && n == 2) X_C8_AND; \
else if(o == 8 && n == 3) X_C8_XOR; \
else if(o == 8 && n == 4) X_C8_ADD; \
else if(o == 8 && n == 5) X_C8_SUB; \
else if(o == 8 && n == 6) X_C8_SHR; \
else if(o == 8 && n == 7) X_C8_SUBN; \
else if(o == 8 && n == 0xE) X_C8_SHL; \
else if(o == 9 && n == 0) X_C8_SNE; \
else if(o == 0xD) X_C8_DRW; \
else X_C8_ILL; \
\
X_C8_EPILOGUE; \
}