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/*
* arch/i386/core/i386_timer.c
*
* Use the "System Timer 2" to implement the udelay callback in
* the BIOS timer driver. Also used to calibrate the clock rate
* in the RTDSC timer driver.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2, or (at
* your option) any later version.
*/
FILE_LICENCE ( GPL2_OR_LATER );
#include <stddef.h>
#include <gpxe/timer2.h>
#include <gpxe/io.h>
/* Timers tick over at this rate */
#define TIMER2_TICKS_PER_SEC 1193180U
/* Parallel Peripheral Controller Port B */
#define PPC_PORTB 0x61
/* Meaning of the port bits */
#define PPCB_T2OUT 0x20 /* Bit 5 */
#define PPCB_SPKR 0x02 /* Bit 1 */
#define PPCB_T2GATE 0x01 /* Bit 0 */
/* Ports for the 8254 timer chip */
#define TIMER2_PORT 0x42
#define TIMER_MODE_PORT 0x43
/* Meaning of the mode bits */
#define TIMER0_SEL 0x00
#define TIMER1_SEL 0x40
#define TIMER2_SEL 0x80
#define READBACK_SEL 0xC0
#define LATCH_COUNT 0x00
#define LOBYTE_ACCESS 0x10
#define HIBYTE_ACCESS 0x20
#define WORD_ACCESS 0x30
#define MODE0 0x00
#define MODE1 0x02
#define MODE2 0x04
#define MODE3 0x06
#define MODE4 0x08
#define MODE5 0x0A
#define BINARY_COUNT 0x00
#define BCD_COUNT 0x01
static void load_timer2 ( unsigned int ticks ) {
/*
* Now let's take care of PPC channel 2
*
* Set the Gate high, program PPC channel 2 for mode 0,
* (interrupt on terminal count mode), binary count,
* load 5 * LATCH count, (LSB and MSB) to begin countdown.
*
* Note some implementations have a bug where the high bits byte
* of channel 2 is ignored.
*/
/* Set up the timer gate, turn off the speaker */
/* Set the Gate high, disable speaker */
outb((inb(PPC_PORTB) & ~PPCB_SPKR) | PPCB_T2GATE, PPC_PORTB);
/* binary, mode 0, LSB/MSB, Ch 2 */
outb(TIMER2_SEL|WORD_ACCESS|MODE0|BINARY_COUNT, TIMER_MODE_PORT);
/* LSB of ticks */
outb(ticks & 0xFF, TIMER2_PORT);
/* MSB of ticks */
outb(ticks >> 8, TIMER2_PORT);
}
static int timer2_running ( void ) {
return ((inb(PPC_PORTB) & PPCB_T2OUT) == 0);
}
void timer2_udelay ( unsigned long usecs ) {
load_timer2 ( ( usecs * TIMER2_TICKS_PER_SEC ) / ( 1000 * 1000 ) );
while (timer2_running()) {
/* Do nothing */
}
}
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