libcaca/kernel/drivers/timer.c

/* 
 *  libcaca       
 *  libcaca       Colour ASCII-Art library
 *  Copyright (c) 2006 Sam Hocevar <sam@hocevar.net>
 *                2009 Jean-Yves Lamoureux <jylam@lnxscene.org>
 *                All Rights Reserved
 *
 *  $Id: kernel.h 4154 2009-12-20 13:33:11Z jylam $
 *
 *  This library is free software. It comes without any warranty, to
 *  the extent permitted by applicable law. You can redistribute it
 *  and/or modify it under the terms of the Do What The Fuck You Want
 *  To Public License, Version 2, as published by Sam Hocevar. See
 *  http://sam.zoy.org/wtfpl/COPYING for more details.
 */

#include "kernel.h"
#include "klibc.h"
#include "timer.h"

u32 ticks = 0;

void timer_phase(int hz)
{
    unsigned int divisor = 1193180 / hz;        /* Calculate our divisor */
    /* 
       0x43 is the Mode/Command register

       From
       http://wiki.osdev.org/Programmable_Interval_Timer#Read_Back_Status_Byte 
       : Bits Usage 6 and 7 Select channel : 0 0 = Channel 0 0 1 = Channel 1
       1 0 = Channel 2 1 1 = Read-back command (8254 only) 4 and 5 Access mode 
       : 0 0 = Latch count value command 0 1 = Access mode: lobyte only 1 0 =
       Access mode: hibyte only 1 1 = Access mode: lobyte/hibyte 1 to 3
       Operating mode : 0 0 0 = Mode 0 (interrupt on terminal count) 0 0 1 =
       Mode 1 (hardware re-triggerable one-shot) 0 1 0 = Mode 2 (rate
       generator) 0 1 1 = Mode 3 (square wave generator) 1 0 0 = Mode 4
       (software triggered strobe) 1 0 1 = Mode 5 (hardware triggered strobe)
       1 1 0 = Mode 2 (rate generator, same as 010b) 1 1 1 = Mode 3 (square
       wave generator, same as 011b) 0 BCD/Binary mode: 0 = 16-bit binary, 1 = 
       four-digit BCD

     */
    unsigned short command = 0 b00110110;
    outb(0x43, command);
    outb(0x40, divisor & 0xFF); /* Set low byte of divisor */
    outb(0x40, divisor >> 8);   /* Set high byte of divisor */
}