timer.c

// from http://www.jamesmolloy.co.uk/tutorial_html/5.-IRQs%20and%20the%20PIT.html

#include "timer.h"
#include "isr.h"
#include "framebuffer.h"
#include "string.h"
#include "io.h"
#include "log.h"

#define PIT_TIMER_MAX_HZ 1193180
#define PIT_DATA_PORT0 0x40
#define PIT_DATA_PORT1 0x41
#define PIT_DATA_PORT2 0x42
#define PIT_COMMAND_PORT 0x43

#define PIT_REPEAT 0x36

uint32_t tick = 0;

static void timer_cb(registers_t regs) {
  tick++;
  debug("tick: %i\n", tick);
  //printf("h/w interrupt: %i\n", regs.int_no);
}

void init_timer(uint32_t frequency) {
  info("initializing timer.\n");
  register_interrupt_handler(IRQ0, &timer_cb);

  uint32_t divisor = PIT_TIMER_MAX_HZ / frequency;

  outb(PIT_COMMAND_PORT, PIT_REPEAT);

  uint8_t low = divisor & 0xff;
  uint8_t high = (divisor >> 8) & 0xff;

  outb(PIT_DATA_PORT0, low);
  outb(PIT_DATA_PORT0, high);
}