mango/arch/x86_64/pit.c

#include <socks/printk.h>
#include <socks/cpu.h>
#include <arch/ports.h>
#include <arch/irq.h>

static unsigned long long tick_counter = 0;

static int pit_callback(void)
{
	tick_counter++;
	return 0;
}

static irq_hook_t pit_irq_hook = {
	.irq_callback = pit_callback
};

void pit_start(unsigned int hz)
{
	tick_counter = 0;

	unsigned int divisor = 1193180 / hz;

	outportb(0x43, 0x36);
	uint8_t lo = (uint8_t)(divisor & 0xFF);
	uint8_t hi = (uint8_t)((divisor >> 8) & 0xFF);

	outportb(0x40, lo);
	outportb(0x40, hi);

	hook_irq(IRQ0, &pit_irq_hook);
}

void pit_stop(void)
{
	/* lowest possible frequency */
	unsigned int divisor = 1193180;

	outportb(0x43, 0x36);
	uint8_t lo = (uint8_t)(divisor & 0xFF);
	uint8_t hi = (uint8_t)((divisor >> 8) & 0xFF);

	outportb(0x40, lo);
	outportb(0x40, hi);

	unhook_irq(IRQ0, &pit_irq_hook);
}

void pit_wait(unsigned int ticks)
{
	unsigned long long end = tick_counter + ticks;

	while (READ_ONCE(tick_counter) < end) {
	}
}