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Text File | 1990-01-15 | 10.9 KB | 384 lines

HIGH PRECISION TIMER DOCUMENTATION Version 5.5 January 14, 1990 Public Domain by Eagle Performance Software TIMERH High Precision Timer Documentation, Version 5.5 T A B L E O F C O N T E N T S Features . . . . . . . . . . . . . . . . . . . . . . 3 Distribution Files . . . . . . . . . . . . . . . . . 3 Demonstration . . . . . . . . . . . . . . . . . . . . 3 Simple Programming . . . . . . . . . . . . . . . . . 3 How It Works . . . . . . . . . . . . . . . . . . . . 4 Support . . . . . . . . . . . . . . . . . . . . . . . 5 Reference . . . . . . . . . . . . . . . . . . . . . . 5 Revisions . . . . . . . . . . . . . . . . . . . . . . 6 2 TIMERH High Precision Timer Documentation, Version 5.5 FEATURES This high precision timer written in Pascal allows you to time events or programs with 1 micro-second resolution up to 24 hours. The program simply uses the extended resolution of the Intel 8253/8254 timer chip which is the same chip that generates an interrupt for the system timer (every 1/18.2... seconds). Compatibility - TIMERH works on all IBM PC, XT, AT, PS/2, and 3270 PC compatible computers. The source code can be compiled with either Turbo Pascal 5.0, 5.5, or QuickPascal. DISTRIBUTION FILES In this version, TIMERH55.ARC contains: TimerH .pas: Timer unit source code. TimerH .doc: This file. TimeDemo.arc: Demonstration file to show elapsed time. DEMONSTRATION To get a feeling of the timer, let's run the demonstration program that came with the utility. Do the following steps: 1. Make and run TIMEDEMO.PAS. 2. Press RETURN for elapsed time since the beginning of the program. 3. Press ESC to quit the program. SIMPLE PROGRAMMING Basically, to time a given event in your program, the source code should look like the following: ... begin ... Timer (Sync); { Optional one time use } Timer (Start); ... { Code to be tested goes here. } ... Timer (Stop); ... end. Start - Timer(Start) resets the initial starting value of T1 so that all subsequent splits will be referenced to this point in time. You can use this more that once. Stop - Timer(Stop) takes a split in reference to the last Timer(Start) TIMERH High Precision Timer Page 3 TIMERH High Precision Timer Documentation, Version 5.5 which changes the value of T2. Subsequent uses of Timer(Stop) are permitted, but there is a little overhead for its execution that is not accounted. Sync - Timer(Sync), placed just before the first start, resets the timer at a zero count. It is recommended that you use the default Sync parameter for consistent results. The Sync parameter starts the chip timer zero. This puts the next interrupt (which uses about 15-200 microseconds to update the system timer) at 1/18.2 seconds away. This makes quick events (<1/18.2 seconds) uninterrupted. Since the system timer is independent of the real time clock, it doesn't affect the time of day on your computer. Overhead - The overhead for the elapsed time between the start and stop is kept in the value T0. The global value ElapsedTime excludes the overhead after Timer(Stop). Jitter - Most events will be within plus or minus 3 microseconds depending on your CPU. HOW IT WORKS To work both on IBM PC which use the 8253 chip and on the IBM AT using the 8254 chip, it is necessary to use the common characteristics of both chips: 1. The output port to the timer for counter 0 which is a utility counter is $43 and the input port is $40. The latch code is $00 to read a value from the chip. 2. The system timer is a four-byte value and updated in memory at 0040h:006Ch, but only the first three bytes (21 bits) are used because it only counts up to 1573040 (1800AFh) ticks per day. At that resolution, it only amounts to: 1573040/(60*60*24) = 18.206481481 ticks/sec 3. The chip counts down from $0000 negatively until it wraps to zero again which then sends the usual interrupt every 1/18.2... seconds to update the system timer in the BIOS data area. 4. Using the chip ports, we can access and lock on to the count down timer and get a value. Since it has one full word in the count, the total extended resolution of 16 bits is: 1573040 * 2^16 = 103090749440 ticks/day = 1193179.9704 ticks/sec 5. This total resolution requires a five-byte value to hold the 37 bit number. If two days are needed in the calculation which is required when passing midnight, a 38 bit value will be needed, but notice that it never reaches the full 40 bits of five bytes. This means that 6 byte reals are fully capable of handling the value with no loss in resolution. TIMERH High Precision Timer Page 4 TIMERH High Precision Timer Documentation, Version 5.5 6. Interrupt control while taking splits was a problem. Since the chip and CPU are independent, it is possible that the chip may try to send an interrupt on the bus just as the OUT code is being executed. The chip will read 0-2 microseconds, but the DOS timer will be one tick short. An easy solution is to take two readings of the DOS timer low byte and see if they differ - one before the chip is latched and another after. If they differ, an extra tick is needed for the system timer part of the split only the timer value is small enough (<10000 microseconds) to confirm that the interrupt did occur. 7. It is also important that no conditional statements are used in the code so that the overhead is constant. 8. The wake up mode of all timer chips is mode 3, but there is no way to use mode 3 on the 8253 with software. The 8254 chip made mode 3 superior with access to its status register, but software accessing this register is incompatible with the IBM PC. So, TIMERH initializes with the common mode 2. When the program is terminated, it is restored back to mode 3 in case anything else may expect the default mode. SUPPORT If you have questions, comments, or suggestions, the Eagle can be contacted by four means - (1) CompuServe, (2) telephone, (3) The Eagle BBS, or (4) mail. CompuServe - The most dependable way to contact the Eagle is through CompuServe. James (Jim) H. LeMay has written the Pascal version of TIMERH, but the person to contact is Jordan Gallagher who can be contacted on the Borland Forum by typing GO BPROGA from the CompuServe main menu. You will enter the Forum for Turbo Pascal. You can contact Jordan with his PPN number of 73557,2342. Messages can also be left through EasyPlex. Telephone - Jordan can also be reached by phone at (214) 539-7855 on weekdays and Saturday from 9:00 a.m. to 8:00 p.m CST. The Eagle BBS - You can also contact us on our 24-hour BBS at (214) 539- 9878, 1200/2400 N81. Mail - For problems, please write: Eagle Performance Software P.O. Box 292786 Lewisville, TX 75029-2786 REFERENCE For more information on the Intel 8253/8254 timer chips, refer to the Intel Microsystem Component Handbook, vol 2. You can also call Intel literature sales at 1-800-548-4725. TIMERH High Precision Timer Page 5 TIMERH High Precision Timer Documentation, Version 5.5 REVISIONS Version 5.5 (01-15-90): Original release. TIMERH High Precision Timer Page 6 ----------------end-of-author's-documentation--------------- Software Library Information: This disk copy provided as a service of Public (software) Library We are not the authors of this program, nor are we associated with the author in any way other than as a distributor of the program in accordance with the author's terms of distribution. Please direct shareware payments and specific questions about this program to the author of the program, whose name appears elsewhere in this documentation. 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