Dear David,
Thanks for the suggestion, IT WORKED!
latency reduced to 4 uSec that's huge. and yes, I made mistake in pasting
the code and removing the comments.
Thanks a ton.
Reposting the code bellow:
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>
int main()
{
struct timespec sT, eT
clock_gettime(CLOCK_REALTIME, &sT);
// printf("\n%ld.%09ld\n" ,sT.tv_sec,sT.tv_nsec);
clock_gettime(CLOCK_REALTIME, &eT);
printf("\n%ld.%09ld %ld uSec\n" , eT.tv_sec, eT.tv_nsec, ((eT.tv_sec -
sT.tv_sec)*1000000 +(eT.tv_nsec-sT.tv_nsec)/1000));
return 0;
}
Regards,
Rathin
On Friday, May 19, 2017 at 12:10:10 PM UTC+5:30, David McQuate wrote:
>
> I suggest you call clock_gettime () twice with nothing between these
> calls. printf() is a complicated function that may interact with hardware,
> for example, a serial port or ethernet. The time required to do input or
> output may depend on the state of the hardware, or on the operation of a
> queue, or maybe even task switching that happens when the system waits for
> I/O.
>
> ( I don't see the definition of sT and eT. Are they declred as pointers
> to startTIme and stopTime ?)
>
>
> Rathin Dholakia <rathind...@gmail.com <javascript:>> wrote:
>>
>> Dear All,
>>
>> I was experimenting with the timing and timing accuracy on BBB. and I
>> came across a very *interesting* yet strange thing!
>>
>> Just running clock_gettime()twice and measuring the time difference,
>> gives you horrendous timing. Here is my simple C code:
>>
>> #include <stdio.h>
>> #include <stdlib.h>
>> #include <math.h>
>> #include <time.h>
>>
>>
>> int main()!
>> {
>>
>>
>> struct timeval startTime, stopTime;
>>
>>
>> clock_gettime(CLOCK_REALTIME, &sT);
>> printf("\n%ld.%09ld\n" ,sT.tv_sec,sT.tv_nsec);
>>
>> clock_gettime(CLOCK_REALTIME, &eT);
>> printf("\n%ld.%09ld %ld uSec\n" , eT.tv_sec, eT.tv_nsec, ((eT.tv_sec
>> - sT.tv_sec)*1000000 + (eT.tv_nsec-sT.tv_nsec)/1000));
>>
>>
>> return 0;
>> }
>>
>> Just two gettime are causing *2894 to 3200 micro sec* (uSec) time
>> difference, how is such huge amount possible!??
>>
>> Can someone throw some light on this? and can it be improved or fixed?
>>
>> I have tried the following to investigate.
>>
>> 1) Running same code on my i7
>> it gives 80uS to ~300 uS delay.
>>
>> 2) Trying TimeVal and GetTimeOfDay -- gives worse result!
>>
>> 3) Running NTP:
>> No impact.
>>
>> Thank you, and hope you find it interesting as well :)
>>
>> --
>> For more options, visit http://beagleboard.org/discuss
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