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   Дата и Время    >>    optimr
 OpTimer v1.0 - High-Resolution Timing  Kim Kokkonen 02.10.1992

Модуль для высокоточных отсчетов времени в среде DOS. Обеспечивает точность до 1 микросекунды за счет перепрограммирования микросхемы таймера.
OPTIMER - Routines for high-resolution timing of events


OPTIMER - Routines for high-resolution timing of events ------------------------------------------------------- Brian Foley and Kim Kokkonen TurboPower Software 1/90 Version 1.0 Released to the public domain Overview -------------------------------------------------------------- One problem commonly faced when trying to run benchmarks on a PC is that, by default, the system clock is accurate only to 1/18th of a second. The OPTIMER unit provides a simple and convenient means of timing events with microsecond resolution. It does this by reprogramming the timer chip, but the gory details are hidden from you. OPTIMER automatically reprograms the timer before your program starts, then restores it to its normal state when your program ends. Unless your program is working with the timer chip at a very low level, no incompatibilities should arise, nor should the performance of your program change. Using OPTIMER -------------------------------------------------------------- OPTIMER is very easy to use. You just add it to your program's USES statement and call the ReadTimer function when you are ready to start/stop timing. For a simple demonstration of how to use OPTIMER, see BENCH.PAS. OPTIMER interfaces the following routines: function ReadTimer : LongInt; {-Read the timer with 1 microsecond resolution} function ElapsedTime(Start, Stop : LongInt) : Real; {-Calculate time elapsed (in milliseconds) between Start and Stop} function ElapsedTimeString(Start, Stop : LongInt) : string; {-Return time elapsed (in milliseconds) between Start and Stop as a string} procedure InitializeTimer; {-Reprogram the timer chip to allow 1 microsecond resolution} procedure RestoreTimer; {-Restore the timer chip to its normal state} The first three of these are probably the only ones you'll ever need to use. InitializeTimer is executed automatically before your program begins, RestoreTimer when it ends. You shouldn't call these yourself unless you want to reset the timer to its normal state temporarily, as you might before using the Exec procedure in the DOS unit: RestoreTimer; Exec(); InitializeTimer; Limitations ----------- Because long integers are used to represent time, OPTIMER cannot be used to time events longer than about 60 minutes: 4,294,967,295 (= $FFFFFFFF, largest unsigned value represented by longint) / 1,193,181 (timer resolution in counts/second) --------------- 3,599 / 60 (seconds/minute) ------- 59.9 minutes This should hardly be a problem, however, since an event longer than an hour presumably doesn't need to be timed with 1-microsecond accuracy anyway. Also note that the process of reading the time takes time. Hence, results of timing very short events will be skewed by the overhead of reading the timer. OPTIMER executes a calibration routine to try to compensate for this overhead as much as possible. This routine estimates the amount of time required to read the timer twice, and uses this value in ElapsedTime and ElapsedTimeString to adjust for the overhead. Even so, you should expect an error due to overhead of about 1-4 ms.