minix/kernel/arch/i386/clock.c
Ben Gras c4fb567bd5 . replace HZ by runtime system_hz (sysenv variable 'hz')
. new flag PROC_FULLVM in table indicating process wants full address
   space (this is then created and managed by VM)
2008-12-11 14:15:23 +00:00

65 lines
2.1 KiB
C
Executable file

/* i386-specific clock functions. */
#include <ibm/ports.h>
#include <minix/portio.h>
#include "../../kernel.h"
#define CLOCK_ACK_BIT 0x80 /* PS/2 clock interrupt acknowledge bit */
/* Clock parameters. */
#define COUNTER_FREQ (2*TIMER_FREQ) /* counter frequency using square wave */
#define LATCH_COUNT 0x00 /* cc00xxxx, c = channel, x = any */
#define SQUARE_WAVE 0x36 /* ccaammmb, a = access, m = mode, b = BCD */
/* 11x11, 11 = LSB then MSB, x11 = sq wave */
#define TIMER_FREQ 1193182 /* clock frequency for timer in PC and AT */
#define TIMER_COUNT (TIMER_FREQ/system_hz) /* initial value for counter*/
/*===========================================================================*
* arch_init_clock *
*===========================================================================*/
PUBLIC int arch_init_clock(void)
{
/* Initialize channel 0 of the 8253A timer to, e.g., 60 Hz,
* and register the CLOCK task's interrupt handler to be run
* on every clock tick.
*/
outb(TIMER_MODE, SQUARE_WAVE); /* run continuously */
outb(TIMER0, (TIMER_COUNT & 0xff)); /* timer low byte */
outb(TIMER0, TIMER_COUNT >> 8); /* timer high byte */
return OK;
}
/*===========================================================================*
* clock_stop *
*===========================================================================*/
PUBLIC void clock_stop(void)
{
/* Reset the clock to the BIOS rate. (For rebooting.) */
outb(TIMER_MODE, 0x36);
outb(TIMER0, 0);
outb(TIMER0, 0);
}
/*===========================================================================*
* read_clock *
*===========================================================================*/
PUBLIC clock_t read_clock(void)
{
/* Read the counter of channel 0 of the 8253A timer. This counter
* counts down at a rate of TIMER_FREQ and restarts at
* TIMER_COUNT-1 when it reaches zero. A hardware interrupt
* (clock tick) occurs when the counter gets to zero and restarts
* its cycle.
*/
u32_t count;
outb(TIMER_MODE, LATCH_COUNT);
count = inb(TIMER0);
count |= (inb(TIMER0) << 8);
return count;
}