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Annotation of coherent/f/etc/conf/streams/src/hr_timer.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * This file contains routines which define a simple high-precision timer
        !             3:  * for PC systems, with appropriate definitions for working under a variety
        !             4:  * of different operating environments.
        !             5:  *
        !             6:  * The basic idea, which is discussed in (among other places)
        !             7:  *     "Accurately Timing Windows Events Without Timer Reprogramming"
        !             8:  *     Jerry Jongerius,
        !             9:  *     Microsoft Systems Journal,
        !            10:  *     July 1991.
        !            11:  * is to read the count register of counter/timer channel 0 on the PC, which
        !            12:  * is normally set up to generate a divide-by-65536 signal from a 1.19318MHz
        !            13:  * timebase, ie. the infamous 18.2Hz timer tick.
        !            14:  *
        !            15:  * While it is possible to read this value with low overhead if you have some
        !            16:  * cooperation from the timer tick handler, it's not too tough for normal
        !            17:  * application code to get at this, as long as it is possible to disable
        !            18:  * interrupts for a short time. This is only necessary to prevent disruption
        !            19:  * to the technique from other subsystems that use it as well.
        !            20:  */
        !            21: 
        !            22: /*
        !            23:  * Locate the system-dependent header files we need depending on the
        !            24:  * operating environment we are being compiled under.
        !            25:  */
        !            26: 
        !            27: #include <ccompat.h>
        !            28: 
        !            29: #define        INT_FLAG_BIT_MASK               0x200
        !            30: 
        !            31: #if    defined (__GNUC__) && defined (GNUDOS)
        !            32: 
        !            33: #include <pc.h>
        !            34: #include <dos.h>
        !            35: 
        !            36: #define        INPUT_BYTE(port)        inportb (port)
        !            37: #define        OUTPUT_BYTE(port,byte)  outportb (port, byte)
        !            38: 
        !            39: static inline unsigned short SPL7 (void) {
        !            40:         register unsigned short temp;
        !            41:         asm ("pushf; pop %0; cli" : "=r" (temp));
        !            42:         return temp;
        !            43: }
        !            44: 
        !            45: static inline void SPLX (unsigned short prev) {
        !            46:         if ((prev & INT_FLAG_BIT_MASK) != 0)
        !            47:                 asm ("sti");
        !            48: }
        !            49: 
        !            50: #define        BIOS_CLOCK_INT  0x1A
        !            51: 
        !            52: static inline unsigned short GETTICKCOUNT (void) {
        !            53:        union REGS in;
        !            54:         in.h.ah = 0;
        !            55:         int86 (BIOS_CLOCK_INT, & in, & in);
        !            56:         return in.x.dx;
        !            57: }
        !            58: 
        !            59: #elif  __BORLANDC__
        !            60: 
        !            61: #include <dos.h>
        !            62: #include <conio.h>
        !            63: 
        !            64: #define        INPUT_BYTE(port)        inportb (port)
        !            65: #define        OUTPUT_BYTE(port,byte)  outportb (port, byte)
        !            66: 
        !            67: #define SPL7()         (_AX = _FLAGS, disable (), _AX)
        !            68: #define SPLX(s)                ((s & INT_FLAG_BIT_MASK) != 0 ? enable () : (void) 0)
        !            69: 
        !            70: #define        BIOS_DATA_SEGMENT       0x40
        !            71: #define        BIOS_TICK_COUNT_LOW     0x6C
        !            72: #define        GETTICKCOUNT()          * (unsigned short far *) MK_FP (BIOS_DATA_SEGMENT, BIOS_TICK_COUNT_LOW)
        !            73: 
        !            74: #else
        !            75: #error unknown system type
        !            76: #endif
        !            77: 
        !            78: /*
        !            79:  * Returns a 32-bit unsigned value which combines the BIOS tick count with
        !            80:  * the current count value from the CTC. Since we do not have the cooperation
        !            81:  * of the tick interrupt handler, we detect overflows by reading the BIOS
        !            82:  * count before and after; we examine the sign of the value we read from the
        !            83:  * CRTC to decide which side of the fence we fell on.
        !            84:  *
        !            85:  * The BIOS tick count is actually 32-bit, but the low 16-bit part only
        !            86:  * overflows about once per hour, so who cares?
        !            87:  */
        !            88: 
        !            89: #define        CTC_PORT_CMD    0x43
        !            90: #define        CTC_PORT_0      0x40
        !            91: #define        CTC_READ_CMD    0xC2
        !            92: 
        !            93: #ifdef __USE_PROTO
        !            94: unsigned long getTickCount (void)
        !            95: #else
        !            96: unsigned long
        !            97: getTickCount ()
        !            98: #endif
        !            99: {
        !           100:        register unsigned short microcount;
        !           101:         unsigned short tickcount, tickcount2;
        !           102:         register short s;
        !           103: 
        !           104:         tickcount = GETTICKCOUNT ();
        !           105: 
        !           106:         /*
        !           107:          * Once we are in a critical section, issue the read (which locks the
        !           108:          * current values in the registers until the read completes).
        !           109:          */
        !           110: 
        !           111:         s = SPL7 ();
        !           112: 
        !           113:         OUTPUT_BYTE (CTC_PORT_CMD, CTC_READ_CMD);
        !           114:         microcount = (INPUT_BYTE (CTC_PORT_0) & 0x80) != 0 ? 0x8000 : 0;
        !           115:         microcount |= INPUT_BYTE (CTC_PORT_0) >> 1;
        !           116:         microcount |= INPUT_BYTE (CTC_PORT_0) << 7;
        !           117: 
        !           118:        SPLX (s);
        !           119: 
        !           120:         if ((microcount & 0x7FFF) == 0)
        !           121:                microcount |= 0x7FFF;
        !           122: 
        !           123:         /*
        !           124:          * Turn the count-down into a count-up.
        !           125:          */
        !           126: 
        !           127:         microcount = ~ microcount;
        !           128: 
        !           129:         /*
        !           130:          * See if we need to cope with a timer wraparound condition.
        !           131:          */
        !           132: 
        !           133:         if ((tickcount2 = GETTICKCOUNT ()) != tickcount) {
        !           134:                /*
        !           135:                  * OK, now which BIOS tick did our measurement fall into?
        !           136:                  * Since the CTC is a upcount from zero, if the value we
        !           137:                  * read has the high bit clear, go with the new value,
        !           138:                 * otherwise use the old one.
        !           139:                  */
        !           140: 
        !           141:                 if ((microcount & 0x8000) == 0)
        !           142:                        tickcount = tickcount2;
        !           143:         }
        !           144: 
        !           145:         return ((unsigned long) tickcount << 16) | microcount;
        !           146: }
        !           147: 
        !           148: /*
        !           149:  * Sit in a loop making sure that the values returned from the timer code
        !           150:  * monotonically increase.
        !           151:  */
        !           152: 
        !           153: #include <stdio.h>
        !           154: 
        !           155: #ifdef __USE_PROTO
        !           156: void main (void)
        !           157: #else
        !           158: void
        !           159: main ()
        !           160: #endif
        !           161: {
        !           162:        unsigned long last, current;
        !           163: 
        !           164:         current = getTickCount ();
        !           165:         while (! kbhit ()) {
        !           166:                last = current;
        !           167:                 current = getTickCount ();
        !           168:                 if ((long) (current - last) <= 0) {
        !           169:                        break;
        !           170:                 }
        !           171:         }
        !           172:        printf ("At end : %lx <= %lx\n", current, last);
        !           173: }

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