timer.c

#include "timer.h"
#include "idt.h"
#include "pic.h"
#include "io.h"
#include <stdint.h>

#define PIT_CMD  0x43
#define PIT_CH0  0x40
#define PIT_FREQ 1193182
#define TARGET_HZ 100

static volatile uint32_t tick_count = 0;

void irq0_handler(void) {
    tick_count++;
    pic_send_eoi(0);
}

void timer_init(void) {
    uint16_t divisor = PIT_FREQ / TARGET_HZ;

    /* Channel 0, lobyte/hibyte, rate generator (mode 2) */
    outb(PIT_CMD, 0x34);
    outb(PIT_CH0, (uint8_t)(divisor & 0xFF));
    outb(PIT_CH0, (uint8_t)((divisor >> 8) & 0xFF));

    /* Install IRQ0 handler at IDT vector 32 */
    extern void irq0_stub(void);
    idt_set_gate(32, (uint32_t)irq0_stub, 0x08, 0x8E);
}

uint32_t timer_get_uptime(void) {
    return tick_count / TARGET_HZ;
}

uint32_t timer_get_ticks(void) {
    return tick_count;
}