/* Copyright (C) 2004  The KOS Team
 
    This program is free software; you can redistribute it and/or
    modify it under the terms of the GNU General Public License
    as published by the Free Software Foundation; either version 2
    of the License, or (at your option) any later version.
    
    This program 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
    GNU General Public License for more details.
    
    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
    USA. 
 */
 #include <hwcore/ioports.h>
 
 #include "i8254.h"
 
 /** 82c54 clock frequency */
 #define I8254_MAX_FREQ 1193180
 
 /* Ports to communicate with the 82c54 */
 #define I8254_TIMER0  0x40
 #define I8254_TIMER1  0x41
 #define I8254_TIMER2  0x42
 #define I8254_CONTROL 0x43
 
 /**
  * Configure the first timer of the 82c54 chip as a rate generator,
  * which will raise an IRQ0 on a regular periodic basis, as given by
  * the freq parameter. Second (RAM refresh) and third (speaker) timers
  * are left unchanged. Maximum frequency is that of the 8254 clock, ie
  * 1193180 Hz.
  *
  * Ahhh PC systems are nice toys: this maximum "strange" frequency
  * equals that of the NTSC clock (14.31818 MHz) divided by 12. In
  * turn, the famous 4.77 MHz cpu clock frequency of the first IBM PC
  * is this same NTSC frequency divided by 3. Why the NTSC frequency as
  * a base "standard" ? Because the 14.31818 MHz quartz were cheap at
  * that time, and because it allows to simply drive altogether the
  * cpu, the "time of day" timer, and the video signal generators.
  */
 sos_ret_t sos_i8254_set_frequency(unsigned int freq)
 {
   unsigned int nb_tick;
 
   if (freq <= 0)
     return -SOS_EINVAL;
 
   /* Compute counter value */
   nb_tick = I8254_MAX_FREQ / freq;
 
   /* Counter must be between 1 and 65536 */
   if (nb_tick > 65536)
     return -SOS_EINVAL;
   if (nb_tick <= 0)
     return -SOS_EINVAL;
 
   /* The i8254 interprets 0 to mean counter == 65536, because 65536
      cannot be coded on 16bits */
   if (nb_tick == 65536)
     nb_tick = 0;
   
   /* We want to configure timer0, we want to send both LSB+MSB to set
      timer0 freq (-> 0x30), and we configure timer0 in mode 2, ie as a
      rate generator (-> 0x4) ==> 0x34 */
   outb(0x34, I8254_CONTROL);
 
   /* Send LSB of counter first */
   outb((nb_tick & 0xFF), I8254_TIMER0);
 
   /* Send MSB of counter */
   outb((nb_tick >> 8) & 0xFF, I8254_TIMER0);
 
   return SOS_OK;
 }