1.1 --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
     1.2 +++ b/src/timer.c	Mon Nov 21 06:14:01 2011 +0200
     1.3 @@ -0,0 +1,127 @@
     1.4 +/*
     1.5 +256-color 3D graphics hack for real-mode DOS.
     1.6 +Copyright (C) 2011  John Tsiombikas <nuclear@member.fsf.org>
     1.7 +
     1.8 +This program is free software: you can redistribute it and/or modify
     1.9 +it under the terms of the GNU General Public License as published by
    1.10 +the Free Software Foundation, either version 3 of the License, or
    1.11 +(at your option) any later version.
    1.12 +
    1.13 +This program is distributed in the hope that it will be useful,
    1.14 +but WITHOUT ANY WARRANTY; without even the implied warranty of
    1.15 +MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    1.16 +GNU General Public License for more details.
    1.17 +
    1.18 +You should have received a copy of the GNU General Public License
    1.19 +along with this program.  If not, see <http://www.gnu.org/licenses/>.
    1.20 +*/
    1.21 +#include <stdio.h>
    1.22 +#include <stdlib.h>
    1.23 +#include <dos.h>
    1.24 +#include "pit8254.h"
    1.25 +
    1.26 +#define PIT_TIMER_INTR	8
    1.27 +#define DOS_TIMER_INTR	0x1c
    1.28 +
    1.29 +/* macro to divide and round to the nearest integer */
    1.30 +#define DIV_ROUND(a, b) \
    1.31 +	((a) / (b) + ((a) % (b)) / ((b) / 2))
    1.32 +
    1.33 +static void set_timer_reload(int reload_val);
    1.34 +static void cleanup(void);
    1.35 +static void interrupt dos_timer_intr();
    1.36 +static void interrupt timer_irq();
    1.37 +static void interrupt (*prev_timer_intr)();
    1.38 +
    1.39 +static unsigned long ticks;
    1.40 +static unsigned long tick_interval, ticks_per_dos_intr;
    1.41 +static int inum;
    1.42 +
    1.43 +void init_timer(int res_hz)
    1.44 +{
    1.45 +
    1.46 +	disable();
    1.47 +	if(res_hz > 0) {
    1.48 +		int reload_val = DIV_ROUND(OSC_FREQ_HZ, res_hz);
    1.49 +		set_timer_reload(reload_val);
    1.50 +
    1.51 +		tick_interval = DIV_ROUND(1000, res_hz);
    1.52 +		ticks_per_dos_intr = DIV_ROUND(65535L, reload_val);
    1.53 +
    1.54 +		inum = PIT_TIMER_INTR;
    1.55 +		prev_timer_intr = getvect(inum);
    1.56 +		setvect(inum, timer_irq);
    1.57 +	} else {
    1.58 +		tick_interval = 55;
    1.59 +
    1.60 +		inum = DOS_TIMER_INTR;
    1.61 +		prev_timer_intr = getvect(inum);
    1.62 +		setvect(inum, dos_timer_intr);
    1.63 +	}
    1.64 +	enable();
    1.65 +
    1.66 +	atexit(cleanup);
    1.67 +}
    1.68 +
    1.69 +static void cleanup(void)
    1.70 +{
    1.71 +	if(!prev_timer_intr) {
    1.72 +		return; /* init hasn't ran, there's nothing to cleanup */
    1.73 +	}
    1.74 +
    1.75 +	disable();
    1.76 +	if(inum == PIT_TIMER_INTR) {
    1.77 +		/* restore the original timer frequency */
    1.78 +		set_timer_reload(65535);
    1.79 +	}
    1.80 +
    1.81 +	/* restore the original interrupt handler */
    1.82 +	setvect(inum, prev_timer_intr);
    1.83 +	enable();
    1.84 +}
    1.85 +
    1.86 +void reset_timer(void)
    1.87 +{
    1.88 +	ticks = 0;
    1.89 +}
    1.90 +
    1.91 +unsigned long get_msec(void)
    1.92 +{
    1.93 +	return ticks * tick_interval;
    1.94 +}
    1.95 +
    1.96 +static void set_timer_reload(int reload_val)
    1.97 +{
    1.98 +	outportb(PORT_CMD, CMD_CHAN0 | CMD_ACCESS_BOTH | CMD_OP_SQWAVE);
    1.99 +	outportb(PORT_DATA0, reload_val & 0xff);
   1.100 +	outportb(PORT_DATA0, (reload_val >> 8) & 0xff);
   1.101 +}
   1.102 +
   1.103 +static void interrupt dos_timer_intr()
   1.104 +{
   1.105 +	ticks++;
   1.106 +	prev_timer_intr();
   1.107 +}
   1.108 +
   1.109 +/* first PIC command port */
   1.110 +#define PIC1_CMD	0x20
   1.111 +/* end of interrupt control word */
   1.112 +#define OCW2_EOI	(1 << 5)
   1.113 +
   1.114 +static void interrupt timer_irq()
   1.115 +{
   1.116 +	static unsigned long dos_ticks;
   1.117 +
   1.118 +	ticks++;
   1.119 +
   1.120 +	if(++dos_ticks >= ticks_per_dos_intr) {
   1.121 +		/* I suppose the dos irq handler does the EOI so I shouldn't
   1.122 +		 * do it if I am to call the previous function
   1.123 +		 */
   1.124 +		prev_timer_intr();
   1.125 +		dos_ticks = 0;
   1.126 +	} else {
   1.127 +		/* send EOI to the PIC */
   1.128 +		outportb(PIC1_CMD, OCW2_EOI);
   1.129 +	}
   1.130 +}