65 lines
1.1 KiB
C
65 lines
1.1 KiB
C
/* vim: tabstop=4 shiftwidth=4 noexpandtab
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*
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* Programmable Interrupt Timer
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*/
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#include <system.h>
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#include <logging.h>
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#define PIT_A 0x40
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#define PIT_B 0x41
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#define PIT_C 0x42
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#define PIT_CONTROL 0x43
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#define PIT_MASK 0xFF
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#define PIT_SCALE 1193180
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#define PIT_SET 0x36
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#define TIMER_IRQ 0
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#define SUBTICKS_PER_TICK 100
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/*
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* Set the phase (in hertz) for the Programmable
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* Interrupt Timer (PIT).
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*/
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void
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timer_phase(
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int hz
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) {
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int divisor = PIT_SCALE / hz;
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outportb(PIT_CONTROL, PIT_SET);
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outportb(PIT_A, divisor & PIT_MASK);
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outportb(PIT_A, (divisor >> 8) & PIT_MASK);
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}
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/*
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* Internal timer counters
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*/
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unsigned long timer_ticks = 0;
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unsigned char timer_subticks = 0;
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/*
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* IRQ handler for when the timer fires
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*/
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void
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timer_handler(
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struct regs *r
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) {
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if (++timer_subticks == SUBTICKS_PER_TICK) {
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timer_ticks++;
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timer_subticks = 0;
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}
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irq_ack(TIMER_IRQ);
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switch_task(1);
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}
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/*
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* Device installer for the PIT
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*/
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void timer_install() {
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debug_print(NOTICE,"Initializing interval timer");
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irq_install_handler(TIMER_IRQ, timer_handler);
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timer_phase(100); /* 100Hz */
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}
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