lib_i386/pcat_timer.c

   1 /*
   2  * (C) Copyright 2002
   3  * Daniel Engström, Omicron Ceti AB, daniel@omicron.se.
   4  *
   5  * See file CREDITS for list of people who contributed to this
   6  * project.
   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 of
  11  * the License, or (at your option) any later version.
  12  *
  13  * This program is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16  * GNU General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU General Public License
  19  * along with this program; if not, write to the Free Software
  20  * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
  21  * MA 02111-1307 USA
  22  */
  23
  24 #include <common.h>
  25 #include <asm/io.h>
  26 #include <asm/i8254.h>
  27 #include <asm/ibmpc.h>
  28
  29 #define TIMER0_VALUE 0x04aa /* 1kHz 1.9318MHz / 1000 */
  30 #define TIMER2_VALUE 0x0a8e /* 440Hz */
  31
  32 int timer_init(void)
  33 {
  34         /* initialize timer 0 and 2
  35          *
  36          * Timer 0 is used to increment system_tick 1000 times/sec
  37          * Timer 1 was used for DRAM refresh in early PC's
  38          * Timer 2 is used to drive the speaker
  39          * (to stasrt a beep: write 3 to port 0x61,
  40          * to stop it again: write 0)
  41          */
  42         outb (PIT_CMD_CTR0 | PIT_CMD_BOTH | PIT_CMD_MODE2,
  43               PIT_BASE + PIT_COMMAND);
  44         outb (TIMER0_VALUE & 0xff, PIT_BASE + PIT_T0);
  45         outb (TIMER0_VALUE >> 8, PIT_BASE + PIT_T0);
  46
  47         outb (PIT_CMD_CTR2 | PIT_CMD_BOTH | PIT_CMD_MODE3,
  48               PIT_BASE + PIT_COMMAND);
  49         outb (TIMER2_VALUE & 0xff, PIT_BASE + PIT_T2);
  50         outb (TIMER2_VALUE >> 8, PIT_BASE + PIT_T2);
  51
  52         irq_install_handler (0, timer_isr, NULL);
  53         unmask_irq (0);
  54
  55         return 0;
  56 }
  57
  58 static u16 read_pit(void)
  59 {
  60         u8 low;
  61
  62         outb (PIT_CMD_LATCH, PIT_BASE + PIT_COMMAND);
  63         low = inb (PIT_BASE + PIT_T0);
  64
  65         return ((inb (PIT_BASE + PIT_T0) << 8) | low);
  66 }
  67
  68 /* this is not very exact */
  69 void udelay (unsigned long usec)
  70 {
  71         int counter;
  72         int wraps;
  73
  74         if (timer_init_done)
  75         {
  76                 counter = read_pit ();
  77                 wraps = usec / 1000;
  78                 usec = usec % 1000;
  79
  80                 usec *= 1194;
  81                 usec /= 1000;
  82                 usec += counter;
  83
  84                 while (usec > 1194) {
  85                         usec -= 1194;
  86                         wraps++;
  87                 }
  88
  89                 while (1) {
  90                         int new_count = read_pit ();
  91
  92                         if (((new_count < usec) && !wraps) || wraps < 0)
  93                                 break;
  94
  95                         if (new_count > counter)
  96                                 wraps--;
  97
  98                         counter = new_count;
  99                 }
 100         }
 101
 102 }