47 lines
1.3 KiB
C
47 lines
1.3 KiB
C
#include <x86.h>
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#include <trap.h>
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#include <stdio.h>
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#include <picirq.h>
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/* *
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* Support for time-related hardware gadgets - the 8253 timer,
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* which generates interruptes on IRQ-0.
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* */
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#define IO_TIMER1 0x040 // 8253 Timer #1
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/* *
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* Frequency of all three count-down timers; (TIMER_FREQ/freq)
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* is the appropriate count to generate a frequency of freq Hz.
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* */
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#define TIMER_FREQ 1193182
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#define TIMER_DIV(x) ((TIMER_FREQ + (x) / 2) / (x))
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#define TIMER_MODE (IO_TIMER1 + 3) // timer mode port
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#define TIMER_SEL0 0x00 // select counter 0
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#define TIMER_RATEGEN 0x04 // mode 2, rate generator
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#define TIMER_16BIT 0x30 // r/w counter 16 bits, LSB first
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volatile size_t ticks;
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/* *
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* clock_init - initialize 8253 clock to interrupt 100 times per second,
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* and then enable IRQ_TIMER.
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* */
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void
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clock_init(void) {
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// set 8253 timer-chip
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outb(TIMER_MODE, TIMER_SEL0 | TIMER_RATEGEN | TIMER_16BIT);
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// 经过多次试验发现原始的10毫秒一次中断（即除以100）是最准时的，不要擅自改中断频率
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outb(IO_TIMER1, TIMER_DIV(100) % 256);
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outb(IO_TIMER1, TIMER_DIV(100) / 256);
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// initialize time counter 'ticks' to zero
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ticks = 0;
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cprintf("++ setup timer interrupts\n");
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pic_enable(IRQ_TIMER);
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}
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