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Message-ID:	<3C507C76.7F039537@lapo.it>
Date:	Thu, 24 Jan 2002 22:28:22 +0100
From:	Lapo Luchini <lapo AT lapo DOT it>
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To:	cygwin AT cygwin DOT com
Subject:	Re: gettimeofday() does not returns usec resolution
References:	<002d01c1a511$ed628b50$0fa807d5 AT BRAMSCHE>

> > I adapted the code to find exactly the minimum time slice, and not "how well
> > 1ms of retard is seen" (it was a 0ns or 15000ns, this is always 15000ns;
> > moreover printf is out of the "timing" section):
> isn't the time slice about 10ms. ?

Actually is between 15 and 16ms:

try  1: 437687512 - 437703512 = 16000
try  2: 437703512 - 437719512 = 16000
try  3: 437719512 - 437734512 = 15000
try  4: 437734512 - 437750512 = 16000
try  5: 437750512 - 437766512 = 16000
try  6: 437766512 - 437781512 = 15000
try  7: 437781512 - 437797512 = 16000
try  8: 437797512 - 437812512 = 15000
try  9: 437812512 - 437828512 = 16000
try 10: 437828512 - 437844512 = 16000
try 11: 437844512 - 437859512 = 15000
try 12: 437859512 - 437875512 = 16000
try 13: 437875512 - 437891512 = 16000
try 14: 437891512 - 437906512 = 15000
try 15: 437906512 - 437922512 = 16000
try 16: 437922512 - 437937512 = 15000
try 17: 437937512 - 437953512 = 16000
try 18: 437953512 - 437969512 = 16000
try 19: 437969512 - 437984512 = 15000
try 20: 437984512 - 438000512 = 16000

Just try this source:

#include <sys/time.h>

#define TV2LONG(t) ((unsigned long)t.tv_sec)*1000000+((unsigned long)t.tv_usec)

int main() {
 struct timeval tp;
 unsigned long a, b;
 unsigned int n = 1;
 for(n=1; n<=20; n++) {
  gettimeofday(&tp, 0);
  a = TV2LONG(tp);
  do {
   gettimeofday(&tp, 0);
  } while((b = TV2LONG(tp)) <= a);
  printf("try %2d: %ld - %ld = %ld\n", n, a, b, b-a);
 }
 gettimeofday(&tp, 0);
 a = TV2LONG(tp);
 usleep(1000000);
 gettimeofday(&tp, 0);
 b = TV2LONG(tp);
 printf("sleep:  %ld - %ld = %ld usec\n", a, b, b-a);
}

--
Lapo 'Raist' Luchini
lapo AT lapo DOT it (PGP & X.509 keys available)
http://www.lapo.it (ICQ UIN: 529796)



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