timer2.c

Go to the documentation of this file.

/*
 * 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 */
        }
}