Skip to content

HTTPS clone URL

Subversion checkout URL

You can clone with
or
.
Download ZIP
Branch: master
Fetching contributors…

Cannot retrieve contributors at this time

66 lines (27 sloc) 0.986 kB
// Intel 8253/8254/82C54 Programmable Interval Timer (PIT).
// Only used on uniprocessors;
// SMP machines use the local APIC timer.
#include "types.h"
#include "defs.h"
#include "traps.h"
#include "x86.h"
#define IO_TIMER1 0x040 // 8253 Timer #1
// Frequency of all three count-down timers;
// (TIMER_FREQ/freq) is the appropriate count
// to generate a frequency of freq Hz.
#define TIMER_FREQ 1193182
#define TIMER_DIV(x) ((TIMER_FREQ+(x)/2)/(x))
#define TIMER_MODE (IO_TIMER1 + 3) // timer mode port
#define TIMER_SEL0 0x00 // select counter 0
#define TIMER_RATEGEN 0x04 // mode 2, rate generator
#define TIMER_16BIT 0x30 // r/w counter 16 bits, LSB first
void
timer_init(void)
{
// Interrupt 100 times/sec.
outb(TIMER_MODE, TIMER_SEL0 | TIMER_RATEGEN | TIMER_16BIT);
outb(IO_TIMER1, TIMER_DIV(100) % 256);
outb(IO_TIMER1, TIMER_DIV(100) / 256);
pic_enable(IRQ_TIMER);
}
// Blank page
Jump to Line
Something went wrong with that request. Please try again.