git.mutantstargoat.com Git - dosdemo/blob - src/dos/timer.c

   1 #include <stdio.h>
   2 #include <stdlib.h>
   3 #include <assert.h>
   4 #include <conio.h>
   5 #include <dos.h>
   6
   7 #ifdef __WATCOMC__
   8 #include <i86.h>
   9 #endif
  10
  11 #ifdef __DJGPP__
  12 #include <stdint.h>
  13 #include <dpmi.h>
  14 #include <go32.h>
  15 #include <pc.h>
  16 #endif
  17
  18 #include "pit8254.h"
  19
  20 #define PIT_TIMER_INTR  8
  21 #define DOS_TIMER_INTR  0x1c
  22
  23 /* macro to divide and round to the nearest integer */
  24 #define DIV_ROUND(a, b) \
  25         ((a) / (b) + ((a) % (b)) / ((b) / 2))
  26
  27 static void set_timer_reload(int reload_val);
  28 static void cleanup(void);
  29
  30 #ifdef __WATCOMC__
  31 #define INTERRUPT       __interrupt __far
  32
  33 static void INTERRUPT dos_timer_intr();
  34
  35 static void (INTERRUPT *prev_timer_intr)();
  36 #endif
  37
  38 #ifdef __DJGPP__
  39 #define INTERRUPT
  40
  41 static _go32_dpmi_seginfo intr, prev_intr;
  42
  43 #define outp(p, v)      outportb(p, v)
  44 #endif
  45
  46 static void INTERRUPT timer_irq();
  47
  48 static unsigned long ticks;
  49 static unsigned long tick_interval, ticks_per_dos_intr;
  50 static int inum;
  51
  52 void init_timer(int res_hz)
  53 {
  54         _disable();
  55
  56         if(res_hz > 0) {
  57                 int reload_val = DIV_ROUND(OSC_FREQ_HZ, res_hz);
  58                 set_timer_reload(reload_val);
  59
  60                 tick_interval = DIV_ROUND(1000, res_hz);
  61                 ticks_per_dos_intr = DIV_ROUND(65535L, reload_val);
  62
  63                 inum = PIT_TIMER_INTR;
  64 #ifdef __WATCOMC__
  65                 prev_timer_intr = _dos_getvect(inum);
  66                 _dos_setvect(inum, timer_irq);
  67 #endif
  68 #ifdef __DJGPP__
  69                 _go32_dpmi_get_protected_mode_interrupt_vector(inum, &prev_intr);
  70                 intr.pm_offset = (intptr_t)timer_irq;
  71                 intr.pm_selector = _go32_my_cs();
  72                 _go32_dpmi_allocate_iret_wrapper(&intr);
  73                 _go32_dpmi_set_protected_mode_interrupt_vector(inum, &intr);
  74 #endif
  75         } else {
  76                 tick_interval = 55;
  77
  78                 inum = DOS_TIMER_INTR;
  79 #ifdef __WATCOMC__
  80                 prev_timer_intr = _dos_getvect(inum);
  81                 _dos_setvect(inum, dos_timer_intr);
  82 #endif
  83 #ifdef __DJGPP__
  84                 assert(0);
  85 #endif
  86         }
  87         _enable();
  88
  89         atexit(cleanup);
  90 }
  91
  92 static void cleanup(void)
  93 {
  94         if(!inum) {
  95                 return; /* init hasn't ran, there's nothing to cleanup */
  96         }
  97
  98         _disable();
  99         if(inum == PIT_TIMER_INTR) {
 100                 /* restore the original timer frequency */
 101                 set_timer_reload(65535);
 102         }
 103
 104         /* restore the original interrupt handler */
 105 #ifdef __WATCOMC__
 106         _dos_setvect(inum, prev_timer_intr);
 107 #endif
 108 #ifdef __DJGPP__
 109         _go32_dpmi_set_protected_mode_interrupt_vector(inum, &prev_intr);
 110         _go32_dpmi_free_iret_wrapper(&intr);
 111 #endif
 112
 113         _enable();
 114 }
 115
 116 void reset_timer(void)
 117 {
 118         ticks = 0;
 119 }
 120
 121 unsigned long get_msec(void)
 122 {
 123         return ticks * tick_interval;
 124 }
 125
 126 static void set_timer_reload(int reload_val)
 127 {
 128         outp(PORT_CMD, CMD_CHAN0 | CMD_ACCESS_BOTH | CMD_OP_SQWAVE);
 129         outp(PORT_DATA0, reload_val & 0xff);
 130         outp(PORT_DATA0, (reload_val >> 8) & 0xff);
 131 }
 132
 133 #ifdef __WATCOMC__
 134 static void INTERRUPT dos_timer_intr()
 135 {
 136         ticks++;
 137         _chain_intr(prev_timer_intr);   /* DOES NOT RETURN */
 138 }
 139 #endif
 140
 141 /* first PIC command port */
 142 #define PIC1_CMD        0x20
 143 /* end of interrupt control word */
 144 #define OCW2_EOI        (1 << 5)
 145
 146 static void INTERRUPT timer_irq()
 147 {
 148         static unsigned long dos_ticks;
 149
 150         ticks++;
 151
 152 #ifdef __WATCOMC__
 153         if(++dos_ticks >= ticks_per_dos_intr) {
 154                 /* I suppose the dos irq handler does the EOI so I shouldn't
 155                  * do it if I am to call the previous function
 156                  */
 157                 dos_ticks = 0;
 158                 _chain_intr(prev_timer_intr);   /* XXX DOES NOT RETURN */
 159                 return; /* just for clarity */
 160         }
 161 #endif
 162
 163         /* send EOI to the PIC */
 164         outp(PIC1_CMD, OCW2_EOI);
 165 }