37 lines
819 B
C
Executable file
37 lines
819 B
C
Executable file
#include <stdio.h>
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#include <dos.h>
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#include "timer.h"
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#define TIMER_INTERRUPT 0x1c
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#define REG_8253_CTL 0x43
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#define REG_COUNTER0 0x40
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volatile unsigned int timer_counter = 0;
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static void interrupt (*oldTimerISR)() = NULL;
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static void interrupt timer_isr() {
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timer_counter ++;
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oldTimerISR();
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}
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void timer_setrate(unsigned int rate) {
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outp(REG_8253_CTL, 0x3c);
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outp(REG_COUNTER0, rate & 0xff);
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outp(REG_COUNTER0, (rate >> 8) & 0xff);
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}
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static void timer_cleanup() {
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if (oldTimerISR != NULL) {
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setvect(TIMER_INTERRUPT, oldTimerISR);
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timer_setrate(TIMER_18HZ);
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oldTimerISR = NULL;
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}
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}
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void timer_init(unsigned int rate) {
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timer_setrate(rate);
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oldTimerISR = getvect(TIMER_INTERRUPT);
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setvect(TIMER_INTERRUPT, timer_isr);
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atexit(timer_cleanup);
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}
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