Re: milliseconds on Windows

2007-10-23 Thread Brian Ford 
On Tue, 23 Oct 2007, Marcell Missura 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?

 On Mon, 12 Feb 2007, Carlo Florendo wrote:

 snip

 Re: strange bug in gettimeofday function

  Windows could be accurate up to 15 ms or perhaps a little bit more.
  However, it is very difficult to achieve less than 15 ms or microsecond
  accuracy with windows due to the limitation on the OS itself.  Our
  extensive tests on windows clocks and timers reveal that windows cannot
  be accurate to the microsecond level or below 15 ms.
 
  In any case, in my experience, windows cannot be accurate with a
  precision of up to 15 milliseconds.

 I'm sorry, could you repeat that value one more time, just in case someone
 missed it ;-).

 Anyway, I don't think it is relevant to the original thread's question,
 but I can assure you that Windows can be used for accurate timings in down
 to 1 or 2 ms (depending on the OS version).

 /snip

 I'm experiencing pretty much the same thing as this guy. I'm using
 gettimeofday() to construct a timestamp and ran a test just like this:


Maybe try the solution I gave this guy (Carlo Florendo) on the cygwin
list?

 double timestamp;
 struct timeval tv;

 while(1)
 {
  gettimeofday(tv, NULL);
  timestamp = tv.tv_sec + (double)tv.tv_usec/100;
  printf(%f\n, timestamp);
 }

 Output:

 1193149915.220881
 ... many times ...
 1193149915.220881
 1193149915.230881
 ... many times ...
 1193149915.240881

 and so on. The timestamp changes every 10 ms.

 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?

http://cygwin.com/ml/cygwin/2007-02/msg00740.html

-- 
Brian Ford
Lead Realtime Software Engineer
VITAL - Visual Simulation Systems
FlightSafety International
the best safety device in any aircraft is a well-trained crew...

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RE: milliseconds on Windows

2007-10-23 Thread Robert D. Holtz - Lists 

 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?

 On Mon, 12 Feb 2007, Carlo Florendo wrote:

 snip

 Re: strange bug in gettimeofday function

  Windows could be accurate up to 15 ms or perhaps a little bit more.
  However, it is very difficult to achieve less than 15 ms or microsecond
  accuracy with windows due to the limitation on the OS itself.  Our
  extensive tests on windows clocks and timers reveal that windows cannot
  be accurate to the microsecond level or below 15 ms.
 
  In any case, in my experience, windows cannot be accurate with a
  precision of up to 15 milliseconds.

 I'm sorry, could you repeat that value one more time, just in case someone
 missed it ;-).

 Anyway, I don't think it is relevant to the original thread's question,
 but I can assure you that Windows can be used for accurate timings in down
 to 1 or 2 ms (depending on the OS version).

 /snip

 I'm experiencing pretty much the same thing as this guy. I'm using
 gettimeofday() to construct a timestamp and ran a test just like this:


Maybe try the solution I gave this guy (Carlo Florendo) on the cygwin
list?

 double timestamp;
 struct timeval tv;

 while(1)
 {
  gettimeofday(tv, NULL);
  timestamp = tv.tv_sec + (double)tv.tv_usec/100;
  printf(%f\n, timestamp);
 }

 Output:

 1193149915.220881
 ... many times ...
 1193149915.220881
 1193149915.230881
 ... many times ...
 1193149915.240881

 and so on. The timestamp changes every 10 ms.

 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.



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RE: milliseconds on Windows

2007-10-23 Thread Brian Ford 
On Tue, 23 Oct 2007, Robert D. Holtz - Lists wrote:

 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.

Or simply use QueryPerformanceCounter.

 This clock does go down to microsecond granularity.

Sure, there are lots of solutions to measuring time more accurately.

The solution I provided is better suited for scheduling processes as
accurately as Windows allows.

-- 
Brian Ford
Lead Realtime Software Engineer
VITAL - Visual Simulation Systems
FlightSafety International
the best safety device in any aircraft is a well-trained crew...

--
Unsubscribe info:  http://cygwin.com/ml/#unsubscribe-simple
Problem reports:   http://cygwin.com/problems.html
Documentation: http://cygwin.com/docs.html
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Re: milliseconds on Windows

2007-10-23 Thread Tim Prince 
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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