Why can't I sleep correct time using gettimeofday()?

[Stan Huang]

Below is a function from my coworker. It runs well at X86. I ran it at iMX6 and it didn't work because the program usually slept just half or twice the time as I expected. The inaccuracy is too large. How come?

inline void uusleep(int usecs) {
struct timeval tpstart,tpend;

  gettimeofday(&tpstart,NULL);
  long ss = tpstart.tv_sec*1000000 + tpstart.tv_usec + usecs;

  while(1) {
   gettimeofday(&tpend,NULL);
   if( (tpend.tv_sec*1000000 + tpend.tv_usec) >= ss) break;
  }
}