From: mauch AT uni-duisburg DOT de (Michael Mauch)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: usleep() and 95dos problems
Date: Fri, 25 Jul 1997 10:34:37 +0200
Organization: Home, sweet home (via Gesamthochschule Duisburg)
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References: <slrn5tdvon DOT 1hb DOT jmarin AT pyy DOT jmp DOT fi>
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To: djgpp AT delorie DOT com
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On 24 Jul 1997 07:07:03 GMT, jmarin AT pyy DOT jmp DOT fi (Jukka Marin) wrote:

> I'm new to djgpp (and dos programming in general :-)  I'm trying to write
> a packet protocol which requires small, but accurate time delays.  I was
> happy to find the usleep() call - and unhappy to find out it doesn't
> work properly.  Not on my hardware, at least.
> 
> If I have a loop like this:
> 
>     while(1) {
>         printf("huu\n");
>         for (i = 0; i < 1000; i++) usleep(1000);
>     }
> 
> The printf() is being run as fast as it can, it seems - ie. the usleep()
> call doesn't delay the execution at all.  If I change the usleep argument
> to 100000, I get a delay - but I need 1 ms delays, not 100 ms ones.

usleep() does not provide 1 ms delay, because it is based on clock()
which in turn has a resolution of 55 ms. You can use a homebrew version
of usleep(), e.g.:


#include <dpmi.h>
#include "puclock.h"

unsigned int
pusleep(unsigned int _useconds)
{
  uclock_t stop_time = puclock() + _useconds * (uclock_t)UCLOCKS_PER_SEC
/ 1e6;

  while (puclock() < stop_time)
  {
    __dpmi_yield();
  }
  return 0;
}


This code uses the puclock() function posted here a few weeks ago. See
this list's archive at www.delorie.com or drop me a line and I'll send
it to you (ca. 3KB).

uclock() uses the timer chip and does not work inside a Windows/Win95
DOS box, because Windows fiddles with the timer chip. puclock()
overcomes this problem because it uses Virtual Timer Device if it runs
inside a Windows DOS box.

Regards...
		Michael

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