kernel/timer.c

   1 /*
   2  *    Copyright (c) 2008 Joshua Phillips. All rights reserved.
   3  *
   4  *  Redistribution and use in source and binary forms, with or without
   5  *  modification, are permitted provided that the following conditions are
   6  *  met:
   7  *
   8  *    1. Redistributions of source code must retain the above copyright
   9  *       notice, this list of conditions and the following disclaimer.
  10  *    2. Redistributions in binary form must reproduce the above copyright
  11  *       notice, this list of conditions and the following disclaimer in
  12  *       the documentation and/or other materials provided with the
  13  *       distribution.
  14  *
  15  *  THIS SOFTWARE IS PROVIDED "AS IS" AND ANY EXPRESS OR IMPLIED
  16  *  WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  17  *  OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  18  *  DISCLAIMED. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
  19  *  DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  20  *  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
  21  *  GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  22  *  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
  23  *  IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
  24  *  OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
  25  *  IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  26  */
  27
  28 #include "timer.h"
  29 #include "portio.h"
  30 #include "console.h"
  31 #include "interrupt.h"
  32 #include "thread.h"
  33
  34 #define TIMER_IRQ 0
  35 #define TIMER_FREQ 1000
  36 #define CTL 0x43
  37 #define CNT0 0x40
  38 #define CNT1 0x41
  39 #define CNT2 0x42
  40
  41 static tick_t tick = 0; // current tick number
  42 static unsigned long freq; // current timer frequency
  43
  44 tick_t get_tick(void)
  45 {
  46         return tick;
  47 }
  48
  49 static void timer_interrupt(int vector, struct interrupt_stack *is)
  50 {
  51         tick++;
  52     if (preempt_on && (next_preempt <= tick)){
  53         preempt(is);
  54     }
  55         ack_irq(TIMER_IRQ);
  56 }
  57
  58 static void set_frequency(unsigned long new_freq)
  59 {
  60         unsigned short divisor;
  61         divisor = 1193180 / new_freq;
  62         freq = (1193180LL << 32) / divisor;
  63         outb(CTL, 0x36);
  64         outb(CNT0, divisor);
  65         outb(CNT0, divisor >> 8);
  66 }
  67
  68 void timer_sys_start(void)
  69 {
  70         unsigned char p61h;
  71         // Timer's frequency is 1,193,180 Hz
  72         outb(CTL, 0x54);
  73         outb(CNT1, 18); // LSB only clock divisor (?)
  74         tick = 0;
  75         set_interrupt(irq_to_int(TIMER_IRQ), timer_interrupt);
  76         set_frequency(TIMER_FREQ);
  77         unmask_irq(TIMER_IRQ);
  78
  79         outb(CTL, 0xB6);
  80         outb(CNT2, 54);
  81         outb(CNT2, 124);
  82         p61h = inb(0x61);
  83         p61h |= 3;
  84         outb(0x61, p61h);
  85 }
  86