mango/arch/x86_64/pit.c

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

#define PIT_COUNTER0  0x40
#define PIT_CMD       0x43

#define CMD_BINARY    0x00   // Use Binary counter values
#define CMD_BCD       0x01   // Use Binary Coded Decimal counter values

#define CMD_MODE0     0x00   // Interrupt on Terminal Count
#define CMD_MODE1     0x02   // Hardware Retriggerable One-Shot
#define CMD_MODE2     0x04   // Rate Generator
#define CMD_MODE3     0x06   // Square Wave
#define CMD_MODE4     0x08   // Software Trigerred Strobe
#define CMD_MODE5     0x0a   // Hardware Trigerred Strobe

#define CMD_LATCH     0x00
#define CMD_RW_LOW    0x10   // Least Significant Byte
#define CMD_RW_HI     0x20   // Most Significant Byte
#define CMD_RW_BOTH   0x30   // Least followed by Most Significant Byte

#define CMD_COUNTER0  0x00
#define CMD_COUNTER1  0x40
#define CMD_COUNTER2  0x80
#define CMD_READBACK  0xc0

#define PIT_FREQUENCY 1193182

static volatile unsigned long long ticks = 0;

static int pit_callback(void)
{
	clock_advance(1);
	ticks++;

	return 0;
}

static struct irq_hook pit_irq_hook = {.irq_callback = pit_callback};

void pit_start(unsigned int hz)
{
	hook_irq(IRQ0, &pit_irq_hook);

	unsigned int divisor = PIT_FREQUENCY / hz;
	outportb(PIT_CMD, CMD_BINARY | CMD_MODE2 | CMD_RW_BOTH | CMD_COUNTER0);
	outportb(PIT_COUNTER0, divisor);
	outportb(PIT_COUNTER0, divisor >> 8);
}

void pit_stop(void)
{
	unsigned int divisor = PIT_FREQUENCY / 20;
	outportb(PIT_CMD, CMD_BINARY | CMD_MODE4 | CMD_RW_BOTH | CMD_COUNTER0);
	outportb(PIT_COUNTER0, divisor);
	outportb(PIT_COUNTER0, divisor >> 8);

	unhook_irq(IRQ0, &pit_irq_hook);
}