[GitHub] [nuttx] maxikrie commented on issue #8207: usleep accuracy

["maxikrie (via GitHub)" <gi...@apache.org>]

maxikrie commented on issue #8207:
URL: https://github.com/apache/nuttx/issues/8207#issuecomment-1399322500

   This minimal example illustrates the problem:
   
   int main(int argc, FAR char *argv[])
   {
     printf("Hello, World!!\n");
   
     uint32_t N = 1000;
     uint32_t time[N];
     useconds_t sleep_time = 100;
   
     struct timespec t_start;
     clock_gettime(0, &t_start);
     for(int i=0; i < N; i++)
     {
   	  struct timespec t1;
   	  clock_gettime(0, &t1);
   	  usleep(sleep_time);
   	  struct timespec t2;
   	  clock_gettime(0, &t2);
   	  struct timespec dt;
   	  clock_timespec_subtract(&t2, &t1, &dt);
   	  time[i] = dt.tv_nsec/1000;
     }
     struct timespec t_end;
     clock_gettime(0, &t_end);
   
     struct timespec dt;
     clock_timespec_subtract(&t_end, &t_start, &dt);
     printf("Average sleep time: %ld (%ld)\n",  dt.tv_nsec/1000/N, sleep_time);
   
     for(int i=0; i < N; i++)
     {
   	  printf("Iteration %d: sleep time %ld (%ld)\n", i, time[i], sleep_time);
     }
     return 0;
   }
   
   On the stm32f4discovery:usbnsh (with CONFIG_SCHED_TICKLESS=y and CONFIG_USEC_PER_TICK=1) I am getting 124 us sleep instead of 100 us, which I find uprising.


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