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annotate src/timer.c @ 3:a8024271c662

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added timer
author John Tsiombikas <nuclear@member.fsf.org>
date Sat, 16 Mar 2013 03:35:08 +0200
parents
children ba868d348de8
rev   line source
nuclear@3 1 /*
nuclear@3 2 256-color 3D graphics hack for real-mode DOS.
nuclear@3 3 Copyright (C) 2011 John Tsiombikas <nuclear@member.fsf.org>
nuclear@3 4
nuclear@3 5 This program is free software: you can redistribute it and/or modify
nuclear@3 6 it under the terms of the GNU General Public License as published by
nuclear@3 7 the Free Software Foundation, either version 3 of the License, or
nuclear@3 8 (at your option) any later version.
nuclear@3 9
nuclear@3 10 This program is distributed in the hope that it will be useful,
nuclear@3 11 but WITHOUT ANY WARRANTY; without even the implied warranty of
nuclear@3 12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
nuclear@3 13 GNU General Public License for more details.
nuclear@3 14
nuclear@3 15 You should have received a copy of the GNU General Public License
nuclear@3 16 along with this program. If not, see <http://www.gnu.org/licenses/>.
nuclear@3 17 */
nuclear@3 18 #include <stdio.h>
nuclear@3 19 #include <stdlib.h>
nuclear@3 20 #include <conio.h>
nuclear@3 21 #include <dos.h>
nuclear@3 22 #include <i86.h>
nuclear@3 23 #include "pit8254.h"
nuclear@3 24
nuclear@3 25 #define PIT_TIMER_INTR 8
nuclear@3 26 #define DOS_TIMER_INTR 0x1c
nuclear@3 27
nuclear@3 28 /* macro to divide and round to the nearest integer */
nuclear@3 29 #define DIV_ROUND(a, b) \
nuclear@3 30 ((a) / (b) + ((a) % (b)) / ((b) / 2))
nuclear@3 31
nuclear@3 32 static void set_timer_reload(int reload_val);
nuclear@3 33 static void cleanup(void);
nuclear@3 34 static void __interrupt __far timer_irq();
nuclear@3 35 static void __interrupt __far dos_timer_intr();
nuclear@3 36
nuclear@3 37 static void (__interrupt __far *prev_timer_intr)();
nuclear@3 38
nuclear@3 39 static unsigned long ticks;
nuclear@3 40 static unsigned long tick_interval, ticks_per_dos_intr;
nuclear@3 41 static int inum;
nuclear@3 42
nuclear@3 43 void init_timer(int res_hz)
nuclear@3 44 {
nuclear@3 45 _disable();
nuclear@3 46
nuclear@3 47 if(res_hz > 0) {
nuclear@3 48 int reload_val = DIV_ROUND(OSC_FREQ_HZ, res_hz);
nuclear@3 49 set_timer_reload(reload_val);
nuclear@3 50
nuclear@3 51 tick_interval = DIV_ROUND(1000, res_hz);
nuclear@3 52 ticks_per_dos_intr = DIV_ROUND(65535L, reload_val);
nuclear@3 53
nuclear@3 54 inum = PIT_TIMER_INTR;
nuclear@3 55 prev_timer_intr = _dos_getvect(inum);
nuclear@3 56 _dos_setvect(inum, timer_irq);
nuclear@3 57 } else {
nuclear@3 58 tick_interval = 55;
nuclear@3 59
nuclear@3 60 inum = DOS_TIMER_INTR;
nuclear@3 61 prev_timer_intr = _dos_getvect(inum);
nuclear@3 62 _dos_setvect(inum, dos_timer_intr);
nuclear@3 63 }
nuclear@3 64 _enable();
nuclear@3 65
nuclear@3 66 atexit(cleanup);
nuclear@3 67 }
nuclear@3 68
nuclear@3 69 static void cleanup(void)
nuclear@3 70 {
nuclear@3 71 if(!prev_timer_intr) {
nuclear@3 72 return; /* init hasn't ran, there's nothing to cleanup */
nuclear@3 73 }
nuclear@3 74
nuclear@3 75 _disable();
nuclear@3 76 if(inum == PIT_TIMER_INTR) {
nuclear@3 77 /* restore the original timer frequency */
nuclear@3 78 set_timer_reload(65535);
nuclear@3 79 }
nuclear@3 80
nuclear@3 81 /* restore the original interrupt handler */
nuclear@3 82 _dos_setvect(inum, prev_timer_intr);
nuclear@3 83 _enable();
nuclear@3 84 }
nuclear@3 85
nuclear@3 86 void reset_timer(void)
nuclear@3 87 {
nuclear@3 88 ticks = 0;
nuclear@3 89 }
nuclear@3 90
nuclear@3 91 unsigned long get_msec(void)
nuclear@3 92 {
nuclear@3 93 return ticks * tick_interval;
nuclear@3 94 }
nuclear@3 95
nuclear@3 96 static void set_timer_reload(int reload_val)
nuclear@3 97 {
nuclear@3 98 outp(PORT_CMD, CMD_CHAN0 | CMD_ACCESS_BOTH | CMD_OP_SQWAVE);
nuclear@3 99 outp(PORT_DATA0, reload_val & 0xff);
nuclear@3 100 outp(PORT_DATA0, (reload_val >> 8) & 0xff);
nuclear@3 101 }
nuclear@3 102
nuclear@3 103 static void __interrupt __far dos_timer_intr()
nuclear@3 104 {
nuclear@3 105 ticks++;
nuclear@3 106 _chain_intr(prev_timer_intr); /* DOES NOT RETURN */
nuclear@3 107 }
nuclear@3 108
nuclear@3 109 /* first PIC command port */
nuclear@3 110 #define PIC1_CMD 0x20
nuclear@3 111 /* end of interrupt control word */
nuclear@3 112 #define OCW2_EOI (1 << 5)
nuclear@3 113
nuclear@3 114 static void __interrupt __far timer_irq()
nuclear@3 115 {
nuclear@3 116 static unsigned long dos_ticks;
nuclear@3 117
nuclear@3 118 ticks++;
nuclear@3 119
nuclear@3 120 if(++dos_ticks >= ticks_per_dos_intr) {
nuclear@3 121 /* I suppose the dos irq handler does the EOI so I shouldn't
nuclear@3 122 * do it if I am to call the previous function
nuclear@3 123 */
nuclear@3 124 dos_ticks = 0;
nuclear@3 125 _chain_intr(prev_timer_intr); /* DOES NOT RETURN */
nuclear@3 126 } else {
nuclear@3 127 /* send EOI to the PIC */
nuclear@3 128 outp(PIC1_CMD, OCW2_EOI);
nuclear@3 129 }
nuclear@3 130 }