65 lines
984 B
C
65 lines
984 B
C
// Intel 8253/8254/82C54 Programmable Interval Timer (PIT).
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// Only used on uniprocessors;
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// SMP machines use the local APIC timer.
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#include "types.h"
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#include "defs.h"
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#include "traps.h"
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#include "x86.h"
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#define IO_TIMER1 0x040 // 8253 Timer #1
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// Frequency of all three count-down timers;
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// (TIMER_FREQ/freq) is the appropriate count
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// to generate a frequency of freq Hz.
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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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void
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timerinit(void)
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{
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// Interrupt 100 times/sec.
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outb(TIMER_MODE, TIMER_SEL0 | TIMER_RATEGEN | TIMER_16BIT);
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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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picenable(IRQ_TIMER);
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}
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// Blank page
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