xv6-cs450/8253pit.c
kaashoek f70172129c run without lapic and ioapic, if they are not present
if no lapic available, use 8253pit for clock
now xv6 runs both on qemu (uniprocessor) and bochs (uniprocessor and MP)
2006-09-07 01:37:58 +00:00

46 lines
1.7 KiB
C

#include "types.h"
#include "x86.h"
#include "defs.h"
#include "traps.h"
// Register definitions for the Intel
// 8253/8254/82C54 Programmable Interval Timer (PIT).
#define IO_TIMER1 0x040 /* 8253 Timer #1 */
#define IO_TIMER2 0x048 /* 8253 Timer #2 (EISA only) */
//
// 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_CNTR0 (IO_TIMER1 + 0) /* timer 0 counter port */
#define TIMER_CNTR1 (IO_TIMER1 + 1) /* timer 1 counter port */
#define TIMER_CNTR2 (IO_TIMER1 + 2) /* timer 2 counter port */
#define TIMER_MODE (IO_TIMER1 + 3) /* timer mode port */
#define TIMER_SEL0 0x00 /* select counter 0 */
#define TIMER_SEL1 0x40 /* select counter 1 */
#define TIMER_SEL2 0x80 /* select counter 2 */
#define TIMER_INTTC 0x00 /* mode 0, intr on terminal cnt */
#define TIMER_ONESHOT 0x02 /* mode 1, one shot */
#define TIMER_RATEGEN 0x04 /* mode 2, rate generator */
#define TIMER_SQWAVE 0x06 /* mode 3, square wave */
#define TIMER_SWSTROBE 0x08 /* mode 4, s/w triggered strobe */
#define TIMER_HWSTROBE 0x0a /* mode 5, h/w triggered strobe */
#define TIMER_LATCH 0x00 /* latch counter for reading */
#define TIMER_LSB 0x10 /* r/w counter LSB */
#define TIMER_MSB 0x20 /* r/w counter MSB */
#define TIMER_16BIT 0x30 /* r/w counter 16 bits, LSB first */
#define TIMER_BCD 0x01 /* count in BCD */
void
pit8253_timerinit(void)
{
// initialize 8253 clock to 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);
irq_setmask_8259A(irq_mask_8259A & ~(1<<IRQ_TIMER));
}