src/arch/i386/core/timer2.c

   1 /*
   2  * arch/i386/core/i386_timer.c
   3  *
   4  * Use the "System Timer 2" to implement the udelay callback in
   5  * the BIOS timer driver. Also used to calibrate the clock rate
   6  * in the RTDSC timer driver.
   7  *
   8  * This program is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU General Public License as
  10  * published by the Free Software Foundation; either version 2, or (at
  11  * your option) any later version.
  12  */
  13
  14 FILE_LICENCE ( GPL2_OR_LATER );
  15
  16 #include <stddef.h>
  17 #include <gpxe/timer2.h>
  18 #include <gpxe/io.h>
  19
  20 /* Timers tick over at this rate */
  21 #define TIMER2_TICKS_PER_SEC    1193180U
  22
  23 /* Parallel Peripheral Controller Port B */
  24 #define PPC_PORTB       0x61
  25
  26 /* Meaning of the port bits */
  27 #define PPCB_T2OUT      0x20    /* Bit 5 */
  28 #define PPCB_SPKR       0x02    /* Bit 1 */
  29 #define PPCB_T2GATE     0x01    /* Bit 0 */
  30
  31 /* Ports for the 8254 timer chip */
  32 #define TIMER2_PORT     0x42
  33 #define TIMER_MODE_PORT 0x43
  34
  35 /* Meaning of the mode bits */
  36 #define TIMER0_SEL      0x00
  37 #define TIMER1_SEL      0x40
  38 #define TIMER2_SEL      0x80
  39 #define READBACK_SEL    0xC0
  40
  41 #define LATCH_COUNT     0x00
  42 #define LOBYTE_ACCESS   0x10
  43 #define HIBYTE_ACCESS   0x20
  44 #define WORD_ACCESS     0x30
  45
  46 #define MODE0           0x00
  47 #define MODE1           0x02
  48 #define MODE2           0x04
  49 #define MODE3           0x06
  50 #define MODE4           0x08
  51 #define MODE5           0x0A
  52
  53 #define BINARY_COUNT    0x00
  54 #define BCD_COUNT       0x01
  55
  56 static void load_timer2 ( unsigned int ticks ) {
  57         /*
  58          * Now let's take care of PPC channel 2
  59          *
  60          * Set the Gate high, program PPC channel 2 for mode 0,
  61          * (interrupt on terminal count mode), binary count,
  62          * load 5 * LATCH count, (LSB and MSB) to begin countdown.
  63          *
  64          * Note some implementations have a bug where the high bits byte
  65          * of channel 2 is ignored.
  66          */
  67         /* Set up the timer gate, turn off the speaker */
  68         /* Set the Gate high, disable speaker */
  69         outb((inb(PPC_PORTB) & ~PPCB_SPKR) | PPCB_T2GATE, PPC_PORTB);
  70         /* binary, mode 0, LSB/MSB, Ch 2 */
  71         outb(TIMER2_SEL|WORD_ACCESS|MODE0|BINARY_COUNT, TIMER_MODE_PORT);
  72         /* LSB of ticks */
  73         outb(ticks & 0xFF, TIMER2_PORT);
  74         /* MSB of ticks */
  75         outb(ticks >> 8, TIMER2_PORT);
  76 }
  77
  78 static int timer2_running ( void ) {
  79         return ((inb(PPC_PORTB) & PPCB_T2OUT) == 0);
  80 }
  81
  82 void timer2_udelay ( unsigned long usecs ) {
  83         load_timer2 ( ( usecs * TIMER2_TICKS_PER_SEC ) / ( 1000 * 1000 ) );
  84         while (timer2_running()) {
  85                 /* Do nothing */
  86         }
  87 }