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#define _DEFAULT_SOURCE
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <assert.h>
#include <time.h>
#include <endian.h>
#include "bits.c"
#include "fnt.c"
#define C8_RESET_VECTOR 0x200
#define C8_CYCLES_PER_FRAME 1000
typedef struct
{
u16 pc;
u8 sp;
u16 i;
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;
#include "instr.c"
#define V mem.sys.v
#define STACK mem.sys.stack
#define DISPLAY mem.sys.disp
#define FONT mem.sys.font
#define RAM mem.ram
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;
}
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\n", c8->i, c8->sp, c8->dt, c8->st);
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]);
}
}
}
void _c8_loop(chip8* c8, bool disasm, u16 from, u16 len)
{
u16 to = 0;
u16 pc = 0;
assert(c8);
if(disasm)
{
pc = c8->pc;
c8->pc = from;
to = from + len*2;
}
c8->running = true;
while(c8->running)
{
int tmp;
u16 word, instr, nnn;
u8 o, x, y, n, kk;
if(c8->pc >= sizeof(c8->mem))
{
printf("PC Overflow!\n");
c8->running = false;
break;
}
if(c8->pc & 0x0001)
{
printf("PC is not aligned!\n");
c8->running = false;
break;
}
word = *(u16*)(c8->RAM + c8->pc);
instr = be16toh(word);
o = (instr & 0xF000) >> 12;
nnn = (instr & 0x0FFF);
x = (instr & 0x0F00) >> 8;
y = (instr & 0x00F0) >> 4;
n = (instr & 0x000F);
kk = (instr & 0x00FF);
printf("%04X: ", c8->pc);
switch(o)
{
case 1:
printf(" %04X JP 0x%03X\n", instr, nnn);
if(disasm) break;
c8->pc = nnn - 2;
break;
case 2:
printf(" %04X CALL 0x%03X\n", instr, nnn);
if(disasm) break;
c8->STACK[c8->sp++] = c8->pc; /* docs says ++sp then stack[sp] = pc ??? */
c8->pc = nnn - 2;
break;
case 3:
printf(" %04X SE V%x, 0x%02X\n", instr, x, kk);
if(disasm) break;
if(c8->V[x] == kk) c8->pc += 2;
break;
case 5:
printf(" %04X SE V%x, V%x\n", instr, x, y);
if(disasm) break;
if(c8->V[x] == c8->V[y]) c8->pc += 2;
break;
case 6:
printf(" %04X LD V%x, 0x%02X\n", instr, x, kk);
if(disasm) break;
c8->V[x] = kk;
break;
case 7:
printf(" %04X ADD V%x, 0x%02X\n", instr, x, kk);
if(disasm) break;
tmp = (int)c8->V[x] + (int)kk;
c8->V[0xf] = (tmp > 255);
/* c8->V[x] = (u8)tmp; /* spec says Vf not set */
break;
case 8:
{
switch(n)
{
case 4:
printf(" %04X ADD V%x, V%x\n", instr, x, y);
if(disasm) break;
tmp = (int)c8->V[x] + (int)c8->V[y];
c8->V[0xf] = (tmp > 255);
c8->V[x] = (u8)tmp;
break;
default:
printf(" %04X Unknown instruction\n", instr);
if(disasm) break;
c8->running = false;
break;
}
}
break;
case 0xA:
printf(" %04X LD I, 0x%03X\n", instr, nnn);
if(disasm) break;
c8->i = nnn;
break;
case 0xC:
printf(" %04X RND V%x, 0x%02X\n", instr, x, kk);
if(disasm) break;
c8->V[x] = (rand() % 256) & kk;
break;
case 0xD:
printf(" %04X DRW V%x, V%x, %d\n", instr, x, y, n);
if(disasm) break;
/* TODO: implement */
break;
case 0xE:
if(kk == 0x9E)
{
printf(" %04X SKP V%x\n", instr, x);
if(disasm) break;
if(c8->keys & bit(x)) c8->pc += 2;
}
else if(kk == 0xA1)
{
printf(" %04X SKNP V%x\n", instr, x);
if(disasm) break;
if(!(c8->keys & bit(x))) c8->pc += 2;
}
else
{
printf(" %04X Unknown instruction\n", instr);
if(disasm) break;
c8->running = false;
}
break;
case 0xF:
if(kk == 0x07)
{
printf(" %04X LD V%x, DT\n", instr, x);
if(disasm) break;
c8->V[x] = c8->dt;
}
else if(kk == 0x15)
{
printf(" %04X LD DT, V%x\n", instr, x);
if(disasm) break;
c8->dt= c8->V[x];
}
else
{
printf(" %04X Unknown instruction\n", instr);
if(disasm) break;
c8->running = false;
}
break;
default:
printf(" %04X Unknown instruction\n", instr);
if(disasm) break;
c8->running = false;
break;
}
if(!disasm) c8_dump_state(c8, false);
c8->pc += 2;
c8->cycles++;
if((c8->cycles % C8_CYCLES_PER_FRAME) == 0)
{
if(c8->dt) c8->dt--;
if(c8->st) c8->st--;
}
if(disasm && (c8->pc >= to)) c8->running = false;
}
if(disasm) c8->pc = pc;
}
void c8_disam(chip8* c8, u16 from, u16 len) { _c8_loop(c8, true, from, len); }
void c8_loop(chip8* c8) { _c8_loop(c8, false, 0, 0); }
int main(int argc, char** argv)
{
FILE* f = NULL;
chip8 c8 = {0};
srand(time(NULL));
c8_reset(&c8);
if(argc > 1)
{
u64 sz, got = 0;
f = fopen(argv[1], "r");
if(!f) return 1;
fseek(f, 0, SEEK_END);
sz = (u64)ftell(f);
rewind(f);
if(sz >= (sizeof(c8.RAM) - 512)) return 2;
got = fread(c8.RAM + C8_RESET_VECTOR, 1, sz, f);
if(got != sz) return 3;
fclose(f);
}
else
{
c8.RAM[C8_RESET_VECTOR + iota] = 0x60;
c8.RAM[C8_RESET_VECTOR + iota] = 0x04;
c8.RAM[C8_RESET_VECTOR + iota] = 0x61;
c8.RAM[C8_RESET_VECTOR + iota] = 0x03;
c8.RAM[C8_RESET_VECTOR + iota] = 0x72;
c8.RAM[C8_RESET_VECTOR + iota] = 0x01;
c8.RAM[C8_RESET_VECTOR + iota] = 0x80;
c8.RAM[C8_RESET_VECTOR + iota] = 0x14;
c8.RAM[C8_RESET_VECTOR + iota] = 0x30;
c8.RAM[C8_RESET_VECTOR + iota] = 0x10;
c8.RAM[C8_RESET_VECTOR + iota] = 0x12;
c8.RAM[C8_RESET_VECTOR + iota] = 0x04;
}
printf("Disasm:\n");
c8_disam(&c8, C8_RESET_VECTOR, 32);
printf("\nExec:\n");
c8_loop(&c8);
return 0;
}
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