#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <sys/time.h>
#include <signal.h>

typedef uint32_t word;

#define MEMSIZE (1 << 16)
word memory [MEMSIZE];

#define IOAREA 0x01000000

word memr (word a)
{
  if (a >= MEMSIZE)
    {
      switch (a)
        {
        case IOAREA + 0:
          return getchar () & 0xFf;
        default:
          abort ();
        }
    }
  else
    return memory [a];
}

void memw (word a, word w)
{
  if (a >= MEMSIZE)
    {
      switch (a)
        {
        case IOAREA + 0:
          putchar (w & 0xFF);
          fflush (stdout);
          // usleep (1000);
          break;
        default:
          abort ();
        }
    }
  else
    memory [a] = w;
}

#define dprintf (void)

#define NPERTICK 2000           /* [kHz] */

/* Our simulator runs at circa 800MHz */

void sim (void)
{
  word pc = 0;
  word a = 0;
  word b;
  word op;
  uint64_t s;
  int zf = 0, cf = 0;
  int ncycle = 0;

  for (;;)
    {
      op = memr (pc++);
      dprintf ("%.8x op %.8x\n", pc-1, op);
      b = memr (op & 0x0FFFFFFF);
      dprintf ("b  %.8x\n", b);
      switch (op >> 28)
        {
        case 0x0: a = s = (uint64_t)a + (uint64_t)b;                    cf = (s >> 32) & 1; zf = (a == 0); break;
        case 0x1: a = s = (uint64_t)a + (uint64_t)b + (uint64_t)cf;     cf = (s >> 32) & 1; zf = (a == 0); break;
        case 0x2: a = s = (uint64_t)a - (uint64_t)b;                    cf = (s >> 32) & 1; zf = (a == 0); break;
        case 0x3: a = s = (uint64_t)a - (uint64_t)b - (uint64_t)cf;     cf = (s >> 32) & 1; zf = (a == 0); break;

        case 0x4: a = a & b;     zf = (a == 0); break;
        case 0x5: a = a | b;     zf = (a == 0); break;
        case 0x6: a = a ^ b;     zf = (a == 0); break;
        case 0x7: a = a >> 1;    zf = (a == 0); break;

        case 0x8: pc = b; break;
        case 0x9: if (!zf) pc = b; break;
        case 0xA: if (zf) pc = b; break;
        case 0xB: if (cf) pc = b; break;

        case 0xC: a = memr (b); dprintf ("R %.8x %.8x\n", b, a); break;
        case 0xD: memw (b, a); dprintf ("W %.8x %.8x\n", b, a);  break;

        case 0xE:
        case 0xF:
          exit (0);
        }
      ncycle += 3;
      if (ncycle > NPERTICK)
        {
          ncycle = 0;
          pause ();
        }
    }
}

int dosim (void)
{
  FILE *f;
  f = fopen ("core.bin", "r");
  fread (memory, 1, sizeof (memory), f);
  sim ();
  return 0;
}

void handler (int sig)
{
  // printf ("a"); fflush (stdout);
}

int main (void)
{
  int i;
  
  signal (SIGALRM, handler);

  {
    struct itimerval val = { { 0, 1000}, {0, 1} };
    setitimer (ITIMER_REAL, &val, 0);
  }

  dosim ();

  return 0;
}