timer.c

一个微型操作系统源码

/*
 * timer.c - OSV timer driver
 *
 * OSV
 * Copyright (C) 2002 Ciprian DOSOFTEI <[e-mail]>
 * All rights reserved.
 * 
 * http://backster.free.fr/osv
 *
 * This file is part of the OSV project. OSV is free software, also known as
 * "open source"; you can redistribute it and/or modify it under the terms 
 * of the GNU General Public License (GPL), version 2, as published by the Free
 * Software Foundation (FSF). To explore alternate licensing terms, contact 
 * the author at [e-mail] or [phone].
 * 
 * OSV is distributed in the hope that it will be useful, but WITHOUT ANY
 * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE.  See the GPL for more details.  You should have
 * received a copy of the GPL along with OSV; see the file COPYING.  If
 * not, write to the FSF, 59 Temple Place #330, Boston, MA 02111-1307, USA.
 */

#include <timer.h>
#include <types.h>
#include <asm/io.h>

dword TIMER_count; 

static void setPITfreq (const dword);

void initTimer () {
  TIMER_count = 0;
  setPITfreq (1000 / INTERVALSIZE);
}

static void setPITfreq (const dword hz) {
  word tmp;
  PIT_CONTROL control;
  tmp = 1193180 / hz;
  control.fields.counting_style = PIT_CSTYLE_16_BITS;
  control.fields.counter_mode = PIT_CM_MODE3;
  control.fields.counter_access = PIT_CA_RW_0_7_8_15;
  control.fields.counter_select = PIT_CSEL_COUNTER0;
  outb(PIT_CONTROL_REG, control.value); 
  outb(PIT_COUNTER0_REG, LOW_BYTE(tmp));
  outb(PIT_COUNTER0_REG, HI_BYTE(tmp));
}

void delay_msec (const dword msec) {
  dword old_count;
  old_count = TIMER_count;
  while (TIMER_count - old_count < msec)
    ;
}

dword get_count () {
  return TIMER_count;
}