Delay by 1 microsecond in C MIPS Environment - c

Question

I'm trying to port u8glib (graphics library) to MIPS processor, OpenWrt router.
Here's an example in arm environment.
As such, one of the routines I must implement is:
delay_micro_seconds(uint32_t us)
Since this is a high resolution unit of time, how can I do this reliably in my environment? I've tried the following, but I'm not even sure how to validate it:
nanosleep((struct timespec[]){{0, 1000}}, NULL);
How can I validate this approach? If its a bad approach, how could I reliably delay by 1 microsecond in C?
EDIT: I've tried this, but I'm getting strange output, I expect the difference between the two print s to be 1000*10 iterations = 10,000 , but it is actually closer to 670,000 nanoseconds:
int main(int argc, char **argv)
{
long res, resb;
struct timespec ts, tsb;
int i;
res = clock_gettime(CLOCK_REALTIME, &ts);
for(i=0;i<10;i++){
nanosleep((struct timespec[]){{0,1000}}, NULL);
}
resb = clock_gettime(CLOCK_REALTIME, &tsb);
if (0 == res) printf("%ld %ld\n", ts.tv_sec, ts.tv_nsec);
else perror("clock_gettime");
if (0 == resb) printf("%ld %ld\n", tsb.tv_sec, tsb.tv_nsec);
else perror("clock_gettime"); //getting 670k delta instead of 10k for tv_nsec
return 0;
}

Answer 1

I assume that your codes would run under Linux.
First, using clock_getres(2) to find a clock's resolution.
and then, using clock_nanosleep(2) might make more accurate sleep.
To validate the sleep, I suggest you check elapsed time with clock_gettime(2)
res = clock_gettime(CLOCK_REALTIME, &ts);
if (0 == res) printf("%ld %ld\n", ts.tv_sec, ts.tv_nsec);
else perror("clock_gettime");
clock_nanosleep(CLOCK_REALTIME, 0, &delay, NULL);
res = clock_gettime(CLOCK_REALTIME, &ts);
if (0 == res) printf("%ld %ld\n", ts.tv_sec, ts.tv_nsec);
else perror("clock_gettime");
Also, if necessary, you can recompile your kernel with higher HZ configuration.
It would be helpful to read time(7) man page. Especially, The software clock, HZ, and jiffies and High-resolution timers sections.
Though my man pages says that High-resolution timer is not supported under mips architecture but I just googled it and mips-linux support HRT apparently.

Answer 2

Is this sleep synchronous? (I'm not familiar with your platform)
Validation
If you have development tools available, are there any profiling tools included? They can at least help you measure execution time.
You can also loop around your sleep call 1000+ times in a test program. Before you enter the loop, get a timestamp from the system clock. After the loop is done cycling, take another timestamp and compare with the first. Remember the loop itself will have some time overhead, but otherwise this will let you know how accurate (overshoot or undershoot) your sleep is. (If you cycle 1,000,000 time around a 1 microsecond sleep function, you would expect that it finishes quite near to 1 second.
Alternative
Sleep functions are not always perfect to their resolution, but they promise to be simple to use and always get you in the neighborhood of what they say. There are many statements that run much quicker than a microsecond, a++;.
Using a similar method as above, you could easily make a homemade synchronous timer with awesome accuracy using a FOR loop with some pointless statement inside of it. Once you find out how many iterations lands you nearest 1 microsecond, it should never change and you could hardcode a function out of it.
If you intend your delay to be asynchronous with a multi-tasking process in mind, this obviously would not cooperate with the other tasks well.