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