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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 <conio.h>
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21 #include <dos.h>
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22 #include <i86.h>
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23 #include "pit8254.h"
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24
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25 #define PIT_TIMER_INTR 8
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26 #define DOS_TIMER_INTR 0x1c
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27
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28 /* macro to divide and round to the nearest integer */
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29 #define DIV_ROUND(a, b) \
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30 ((a) / (b) + ((a) % (b)) / ((b) / 2))
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31
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32 static void set_timer_reload(int reload_val);
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33 static void cleanup(void);
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34 static void __interrupt __far timer_irq();
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35 static void __interrupt __far dos_timer_intr();
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36
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37 static void (__interrupt __far *prev_timer_intr)();
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38
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39 static unsigned long ticks;
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40 static unsigned long tick_interval, ticks_per_dos_intr;
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41 static int inum;
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42
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43 void init_timer(int res_hz)
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44 {
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45 _disable();
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46
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47 if(res_hz > 0) {
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48 int reload_val = DIV_ROUND(OSC_FREQ_HZ, res_hz);
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49 set_timer_reload(reload_val);
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50
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51 tick_interval = DIV_ROUND(1000, res_hz);
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52 ticks_per_dos_intr = DIV_ROUND(65535L, reload_val);
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53
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54 inum = PIT_TIMER_INTR;
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55 prev_timer_intr = _dos_getvect(inum);
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56 _dos_setvect(inum, timer_irq);
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57 } else {
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58 tick_interval = 55;
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59
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60 inum = DOS_TIMER_INTR;
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61 prev_timer_intr = _dos_getvect(inum);
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62 _dos_setvect(inum, dos_timer_intr);
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63 }
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64 _enable();
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65
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66 atexit(cleanup);
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67 }
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68
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69 static void cleanup(void)
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70 {
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71 if(!prev_timer_intr) {
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72 return; /* init hasn't ran, there's nothing to cleanup */
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73 }
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74
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75 _disable();
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76 if(inum == PIT_TIMER_INTR) {
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77 /* restore the original timer frequency */
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78 set_timer_reload(65535);
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79 }
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80
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81 /* restore the original interrupt handler */
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82 _dos_setvect(inum, prev_timer_intr);
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83 _enable();
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84 }
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85
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86 void reset_timer(void)
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87 {
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88 ticks = 0;
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89 }
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90
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91 unsigned long get_msec(void)
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92 {
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93 return ticks * tick_interval;
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94 }
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95
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96 static void set_timer_reload(int reload_val)
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97 {
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98 outp(PORT_CMD, CMD_CHAN0 | CMD_ACCESS_BOTH | CMD_OP_SQWAVE);
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99 outp(PORT_DATA0, reload_val & 0xff);
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100 outp(PORT_DATA0, (reload_val >> 8) & 0xff);
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101 }
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102
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103 static void __interrupt __far dos_timer_intr()
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104 {
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105 ticks++;
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106 _chain_intr(prev_timer_intr); /* DOES NOT RETURN */
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107 }
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108
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109 /* first PIC command port */
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110 #define PIC1_CMD 0x20
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111 /* end of interrupt control word */
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112 #define OCW2_EOI (1 << 5)
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113
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114 static void __interrupt __far timer_irq()
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115 {
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116 static unsigned long dos_ticks;
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117
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118 ticks++;
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119
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120 if(++dos_ticks >= ticks_per_dos_intr) {
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121 /* I suppose the dos irq handler does the EOI so I shouldn't
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122 * do it if I am to call the previous function
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123 */
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124 dos_ticks = 0;
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125 _chain_intr(prev_timer_intr); /* XXX DOES NOT RETURN */
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126 return; /* just for clarity */
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127 }
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128
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129 /* send EOI to the PIC */
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130 outp(PIC1_CMD, OCW2_EOI);
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131 }
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