Message-ID: <471E9B41.6030205@computer.org>
Date: Tue, 23 Oct 2007 18:09:21 -0700
From: Tim Prince <tprince@computer.org>
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To: cygwin@cygwin.com
Subject: Re: milliseconds on Windows
References: <38624.131.220.7.1.1193151578.squirrel@webmail.iai.uni-bonn.de> <Pine.CYG.4.58.0710231015060.3388@PC1163-8460-XP.flightsafety.com> <000201c81593$045ae260$02fea8c0@DDZG9K91>
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Robert D. Holtz - Lists wrote:
>> Hello Brian,
> 
> http://cygwin.com/acronyms/#PPIOSPE
> 
> I've redirected this message and set the Reply-To appropriately.
> 
>> I'm a student at Bonn university and I'm researching robotics. I'm trying
>> to write a robot controller for Windows XP (wasn't my choice!) and
>> measuring elapsed time down to milliseconds precision is crucial. Do you
>> happen to remember this discussion on the cygwin mailing list?
>>

>> So if you know how to measure 1ms (less would be even better) on Win XP,
>> can you please tell me how to do that?
> 
> If you're feeling frisky it's also possible to write a low level routine
> that hooks the hardware clock and uses it for retrieving the time.
> 
> This clock does go down to microsecond granularity.
> 
As gcc hasn't implemented the Microsoft style __rdtsc() intrinsic, we
use routinely the usual gcc 32-bit-only stuff:

unsigned long long int rdtsc( )
{
   long long a;
   asm volatile("rdtsc":"=A" (a));
   return a;
}

which gives you a number of CPU clock ticks (on current platforms,
typically derived from the buss clock and nominal CPU clock speed ratio).

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