91 lines
2.5 KiB
C++
91 lines
2.5 KiB
C++
// C library headers
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#include <stdio.h>
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#include <stdlib.h>
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#include <time.h>
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#include <errno.h>
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#include <math.h>
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#define NSEC_PER_SEC (1000000000) /* The number of nsecs per sec. */
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static inline void tsnorm(struct timespec *ts)
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{
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while (ts->tv_nsec >= NSEC_PER_SEC) {
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ts->tv_nsec -= NSEC_PER_SEC;
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ts->tv_sec++;
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}
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}
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/* Subtract the ‘struct timeval’ values X and Y, (X-Y)
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storing the result in RESULT.
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Return 1 if the difference is negative, otherwise 0. */
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int timespec_subtract (struct timespec *result, struct timespec *x, struct timespec *y)
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{
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/* Perform the carry for the later subtraction by updating y. */
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if (x->tv_nsec < y->tv_nsec) {
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int n_sec = (y->tv_nsec - x->tv_nsec) / 1000000000 + 1;
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y->tv_nsec -= 1000000000 * n_sec;
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y->tv_sec += n_sec;
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}
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if (x->tv_nsec - y->tv_nsec > 1000000000) {
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int n_sec = (x->tv_nsec - y->tv_nsec) / 1000000000;
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y->tv_nsec += 1000000000 * n_sec;
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y->tv_sec -= n_sec;
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}
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/* Compute the time remaining to wait.
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tv_usec is certainly positive. */
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result->tv_sec = x->tv_sec - y->tv_sec;
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result->tv_nsec = x->tv_nsec - y->tv_nsec;
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/* Return 1 if result is negative. */
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return x->tv_sec < y->tv_sec;
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}
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int main()
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{
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static struct timespec t, t_toc, t_lasttoc, t_duration;
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double us_err, us_err_min=0, us_err_max=0, us_err_avg=0, us_err_rms=0;
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long int n_tocs=0;
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clock_gettime(CLOCK_MONOTONIC ,&t);
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/* start after one second */
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//t.tv_sec++;
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long int period = 500000;
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while(1) {
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//timekeeping//
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t_lasttoc = t_toc;
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clock_gettime(CLOCK_MONOTONIC, &t_toc); //TOC
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n_tocs++;
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timespec_subtract (&t_duration, &t_toc, &t_lasttoc); //get duration
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us_err = ((t_duration.tv_nsec-period)/1000.); //in us
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if (n_tocs > 2) { //do statistics, omit first 2 values
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if (us_err < us_err_min) us_err_min = us_err;
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if (us_err > us_err_max) us_err_max = us_err;
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us_err_avg = (us_err_avg*(n_tocs-1)+us_err)/n_tocs;
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us_err_rms = sqrt(((us_err_rms)*(us_err_rms)*(n_tocs-1)+us_err*us_err)/n_tocs);
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}
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t.tv_nsec += (period); //add a period to the cycle
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tsnorm(&t);
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if (!(n_tocs%500)){
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printf("%+5.2f [us] Min: %+5.2f [us] Max:%+5.2f [us] Avg:%+5.2f [us] RMS: %5.2f [us]\n",us_err, us_err_min, us_err_max, us_err_avg, us_err_rms);
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}
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//The famous sleep till next tick.
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clock_nanosleep(CLOCK_MONOTONIC, TIMER_ABSTIME, &t, &t);
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}
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return 0;
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}
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