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