16f1e35775
We now have two implementations for the timer API: one using the time-of-day counter at 40:70 and one using RDTSC. Both make use of timer2_udelay().
86 lines
2.2 KiB
C
86 lines
2.2 KiB
C
/*
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* arch/i386/core/i386_timer.c
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*
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* Use the "System Timer 2" to implement the udelay callback in
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* the BIOS timer driver. Also used to calibrate the clock rate
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* in the RTDSC timer driver.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2, or (at
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* your option) any later version.
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*/
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#include <stddef.h>
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#include <gpxe/timer2.h>
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#include <gpxe/io.h>
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/* Timers tick over at this rate */
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#define TIMER2_TICKS_PER_SEC 1193180U
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/* Parallel Peripheral Controller Port B */
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#define PPC_PORTB 0x61
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/* Meaning of the port bits */
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#define PPCB_T2OUT 0x20 /* Bit 5 */
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#define PPCB_SPKR 0x02 /* Bit 1 */
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#define PPCB_T2GATE 0x01 /* Bit 0 */
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/* Ports for the 8254 timer chip */
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#define TIMER2_PORT 0x42
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#define TIMER_MODE_PORT 0x43
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/* Meaning of the mode bits */
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#define TIMER0_SEL 0x00
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#define TIMER1_SEL 0x40
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#define TIMER2_SEL 0x80
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#define READBACK_SEL 0xC0
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#define LATCH_COUNT 0x00
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#define LOBYTE_ACCESS 0x10
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#define HIBYTE_ACCESS 0x20
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#define WORD_ACCESS 0x30
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#define MODE0 0x00
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#define MODE1 0x02
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#define MODE2 0x04
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#define MODE3 0x06
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#define MODE4 0x08
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#define MODE5 0x0A
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#define BINARY_COUNT 0x00
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#define BCD_COUNT 0x01
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static void load_timer2 ( unsigned int ticks ) {
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/*
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* Now let's take care of PPC channel 2
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*
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* Set the Gate high, program PPC channel 2 for mode 0,
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* (interrupt on terminal count mode), binary count,
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* load 5 * LATCH count, (LSB and MSB) to begin countdown.
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*
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* Note some implementations have a bug where the high bits byte
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* of channel 2 is ignored.
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*/
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/* Set up the timer gate, turn off the speaker */
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/* Set the Gate high, disable speaker */
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outb((inb(PPC_PORTB) & ~PPCB_SPKR) | PPCB_T2GATE, PPC_PORTB);
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/* binary, mode 0, LSB/MSB, Ch 2 */
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outb(TIMER2_SEL|WORD_ACCESS|MODE0|BINARY_COUNT, TIMER_MODE_PORT);
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/* LSB of ticks */
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outb(ticks & 0xFF, TIMER2_PORT);
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/* MSB of ticks */
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outb(ticks >> 8, TIMER2_PORT);
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}
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static int timer2_running ( void ) {
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return ((inb(PPC_PORTB) & PPCB_T2OUT) == 0);
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}
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void timer2_udelay ( unsigned long usecs ) {
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load_timer2 ( ( usecs * TIMER2_TICKS_PER_SEC ) / ( 1000 * 1000 ) );
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while (timer2_running()) {
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/* Do nothing */
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}
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}
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