Date: Sun, 15 Aug 1999 14:09:13 +0300 (IDT)
From: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
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To: Simon Redwood <spredwood AT sri-net DOT demon DOT co DOT uk>
cc: djgpp AT delorie DOT com
Subject: Re: usleep/delay/sleep ?
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On Sat, 14 Aug 1999, Simon Redwood wrote:

> I am new to using djgpp under dos, being a unix programmer.  I am having
> trouble with delays.
> 
> Can I rely on usleep to give me accurate timings.
> 
> Giving usleep a value of 10000-12500 produces the same delay, whereas 13000
> gives the same as 20000, where I am going wrong.

This is all expected behavior: usleep has a 55-msec granularity.  (This 
is unfortunately not stressed in the docs; v2.03 fixes that.)  The system 
clock on the PC ticks 18.2 times a second, so this is what you get.

> I would like to put a delay into a loop of about 1/100 sec. how is the best
> way to acheive this

Write your own wait loop that calls uclock.  This function has 
840-nanosecond resolution.

> I am also looking to work with microprocessors where I will need accurate
> timings of nanoseconds, how can this be best acheived.

One way is to use the machine instruction that reads the counter register 
of the Pentium and later CPUs.