/*
 *-----------------------------------------------------------------------------
 *
 * timer.c --
 *
 *    Handle the timer interrupt.
 *
 *-----------------------------------------------------------------------------
 */

#include <cpuid.h>

#define TIMER_INTERRUPT 0x20

#define TICK_HZ 64

/* spin at ~8Hz */
#define TICK_MASK 0xf

#define INPUT_TICKS 1193181

void
tick (void)
{
   static unsigned long ticks = 0;
   static unsigned long v = 0;
   char spinner[] = { '|', '/', '-', '\\' };
   char *vgabuf = (char *)0xb8000;

   acknowledge_irq ();

   ticks++;

   if (ticks & TICK_MASK) {
      return;
   }

   vgabuf[0] = spinner[v & 0x3];
   vgabuf[1] = 0x7;

   v++;
}

extern void tick_stub (void);
asm ("   .global tick_stub\n"
     "tick_stub:\n\t"
     "   call    tick\n\t"
     "   iret\n");

void
enable_timer (void)
{
   install_iv (TIMER_INTERRUPT, &tick_stub, INTERRUPT);

   outb (inb (0x21) & 0xfe, 0x21);
}

void
disable_timer (void)
{
   outb (inb (0x21) & 0x01, 0x21);
}

void
set_timer_interval (unsigned long interval)
{
   unsigned long counter;

   if (interval < 19) {
      /* 18.2Hz is as low as this goes */
      interval = 19;
   }

   counter = INPUT_TICKS / interval;

   outb (0x36, 0x43);
   outb ((char)(counter & 0xff), 0x40);
   outb ((char)((counter >> 8) & 0xff), 0x40);
}

void
timer_init (void)
{
   set_timer_interval (TICK_HZ);

   enable_timer ();
}