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| 2 | /***********************************************************************
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| 3 |
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| 4 | $Id: tmrsvcs.c 1521 2010-05-02 21:48:59Z gyoung $
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| 5 |
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| 6 | Timer services
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| 7 |
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| 8 | Copyright (c) 2008 Steven H. Levine
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| 9 |
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| 10 | 05 Jan 08 SHL Baseline
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| 11 |
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| 12 | ***********************************************************************/
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| 13 |
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| 14 | #define INCL_DOS // QSV_MS_COUNT
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| 15 |
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| 16 | // #include "errutil.h" // DbgMsg // 05 Jan 08 SHL fixme debug
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| 17 | #include "tmrsvcs.h"
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| 18 |
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| 19 | // static PSZ pszSrcFile = __FILE__; // 05 Jan 08 SHL fixme debug
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| 20 |
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| 21 | /**
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| 22 | * Prepare interval timer descriptor for use
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| 23 | * Call with interval 0 to to reset internal estimators
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| 24 | * @param pTD point to interval timer descriptor
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| 25 | * @param interval_msec is the timer interval in msec or 0 to retain existing value
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| 26 | */
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| 27 |
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| 28 | VOID InitITimer(ITIMER_DESC *pitd, UINT interval_msec)
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| 29 | {
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| 30 | if (interval_msec) {
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| 31 | // Assume starting new loop at similar rate
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| 32 | pitd->interval_msec = interval_msec;
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| 33 | pitd->remaining = pitd->estimated;
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| 34 | }
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| 35 | else {
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| 36 | // Assume loop rate is changing to a significantly lower value
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| 37 | pitd->remaining = 0;
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| 38 | pitd->estimated = 1; // Force rate recalc
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| 39 | }
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| 40 | DosQuerySysInfo(QSV_MS_COUNT, QSV_MS_COUNT, &pitd->start_msec, sizeof(pitd->start_msec));
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| 41 | }
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| 42 |
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| 43 | /**
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| 44 | * Check timer interval expired
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| 45 | * Attempts to optimize calls to fetch QSV_MS_COUNT
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| 46 | * Caller should reinit if processing rate changes
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| 47 | * @return TRUE if expired
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| 48 | */
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| 49 |
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| 50 | BOOL IsITimerExpired(ITIMER_DESC *pitd)
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| 51 | {
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| 52 | INT err_msec;
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| 53 | ULONG cur_msec;
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| 54 | UINT elapsed_msec;
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| 55 | INT cnt;
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| 56 |
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| 57 | if (--pitd->remaining < 0) {
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| 58 |
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| 59 | DosQuerySysInfo(QSV_MS_COUNT, QSV_MS_COUNT, &cur_msec, sizeof(cur_msec));
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| 60 | elapsed_msec = cur_msec - pitd->start_msec;
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| 61 | if (elapsed_msec == pitd->interval_msec) {
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| 62 | pitd->remaining = pitd->estimated;
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| 63 | pitd->start_msec = cur_msec;
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| 64 | pitd->misses = 0;
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| 65 | return TRUE; // Say interval expired
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| 66 | }
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| 67 |
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| 68 | pitd->misses++;
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| 69 | err_msec = (cur_msec - pitd->start_msec) - pitd->interval_msec;
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| 70 | // Estimate counts per msec
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| 71 | if (err_msec > 0) {
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| 72 | // Late - need to reduce estimated count
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| 73 | if (elapsed_msec)
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| 74 | pitd->estimated = pitd->estimated * pitd->interval_msec / elapsed_msec;
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| 75 | else {
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| 76 | // Should not occur
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| 77 | if (pitd->estimated)
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| 78 | pitd->estimated--;
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| 79 | }
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| 80 | // Calc counts for next interval
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| 81 | pitd->remaining = pitd->estimated -
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| 82 | (pitd->estimated * err_msec / pitd->interval_msec);
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| 83 | pitd->start_msec += pitd->interval_msec;
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| 84 | return TRUE;
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| 85 | }
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| 86 |
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| 87 | // Early - need to increase estimated count
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| 88 | cnt = pitd->estimated * (-err_msec) / pitd->interval_msec;
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| 89 | if (!cnt) {
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| 90 | if (pitd->estimated)
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| 91 | cnt = pitd->estimated * 2;
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| 92 | else
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| 93 | cnt = 1;
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| 94 | }
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| 95 | pitd->estimated += cnt;
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| 96 | pitd->remaining = cnt;
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| 97 | }
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| 98 | return FALSE; // Keep waiting
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| 99 | }
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| 100 |
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| 101 | VOID SleepIfNeeded(ITIMER_DESC *pitd, UINT sleepTime)
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| 102 | {
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| 103 | if (IsITimerExpired(pitd)) {
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| 104 | DosSleep(sleepTime);
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| 105 | InitITimer(pitd, 0);
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| 106 | }
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| 107 | }
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| 108 |
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| 109 | #pragma alloc_text(TMRSVCS,InitITimer,IsITimerExpired,SleepIfNeeded)
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