Acquisition delay every minute 
Author Message
 Acquisition delay every minute

Hi!

I'm using a Dell Inspiron 7500 laptop to acquire data from two
DAQCard-5102 devices (NI 5102 for PCMCIA). We use labview 5.1 together
with NI-DAQ 6.6. The LV code acquires a waveform from each channel of
each card & does some additional processing. The waveform acquisition
must keep up with an external trigger.

I timestamp every waveform to measure the gap between waveforms, and use
s/w triggering to see how fast the code can go.
The time between waveforms is usually very stable at about 27 ms.
Every 60.0 seconds there is an extra delay: the gap between waveforms is
longer, about 37 ms. If I could remove this delay, I could go about 40%
faster and still keep up with the trigger!

I'd welcome your ideas on how to get rid of this delay. Some setting in
the BIOS or Windows?

Here is some extra information:
This delay does not appear an old Dell Inspiron 7000 laptop or on a
desktop system.
The delay appeared under Windows ME; I changed the hard disk to Win98 SE
& it still appeared.
I tried NI-DAQ 6.8.1, and using the NI-Scope 1.6 drivers.
I have LV 6.0 but haven't tried it.
I built the code into an executable.
I couldn't see any relevant BIOS setting; disabled power management.
I stopped the taskbar updating the clock.
I removed every program from StartUp.
I stopped the network card & ejected it.
I removed Windows automatic update, Microsoft Find Fast, & antivirus
software.
I used the simplest video driver that would work.
I used msconfig to minimize the number of processes starting.
I killed every task that I could find in the task list shown by
ctrl-alt-del.
I installed the Microsoft utility wintop; like Task Manager for Windows
9x it shows every program running, and I killed unnecessary ones.
When the delay happens I don't see anything happening; the disk light
doesn't flash.

Look forward to your help!

Thanks Mark



Sun, 01 Jun 2003 06:18:45 GMT  
 Acquisition delay every minute
It "smells" to me like the Windows overhead involved in rolling over the PC
clock ( and checking for minute rollover, hour rollover, redrawing the clock
in the start bar - try getting rid of the clock display too????? ) lurking
under windows. - Anyone else know of anything (left over from what you
deleted of course) that operated at precisely 1 iteration per minute?

This looks like a classic example of why GUI based Operating systems like
Windows can't be trusted for real time applications - for fast stuff like
this (and this is slow) I use a DOS extended mode application developed on a
Watcom compiler in 386 mode run under DOS4GW by Rational (no I don't work
for any of these companies).  Booting up, interrupting the boot with F8 and
starting in "command line only" mode lets me run my application about a 100
times faster than the GUI version.  Unfortunately, an awful lot of vendors
(NI is one) don't support a DOS version of an driver any more and aren't
much help when you try to get communications with their products established
yourself. I have exactly this problem setting up an NI PCI-5411 waveform
generator right now.

The other possibility, a bit remote, is the accuracy of the timestamp
itself - you might be slipping slightly with respect to the PC clock, and
after enough cycles, (1 minute) you pick up a later time tag - I would
expect this to be a bit noisy and overhead-sensitive though. Naturally if
your timetag is e.g. IRIG based, I'm wrong.


Quote:
> Hi!

> I'm using a Dell Inspiron 7500 laptop to acquire data from two
> DAQCard-5102 devices (NI 5102 for PCMCIA). We use LabVIEW 5.1 together
> with NI-DAQ 6.6. The LV code acquires a waveform from each channel of
> each card & does some additional processing. The waveform acquisition
> must keep up with an external trigger.

> I timestamp every waveform to measure the gap between waveforms, and use
> s/w triggering to see how fast the code can go.
> The time between waveforms is usually very stable at about 27 ms.
> Every 60.0 seconds there is an extra delay: the gap between waveforms is
> longer, about 37 ms. If I could remove this delay, I could go about 40%
> faster and still keep up with the trigger!

> I'd welcome your ideas on how to get rid of this delay. Some setting in
> the BIOS or Windows?

> Here is some extra information:
> This delay does not appear an old Dell Inspiron 7000 laptop or on a
> desktop system.
> The delay appeared under Windows ME; I changed the hard disk to Win98 SE
> & it still appeared.
> I tried NI-DAQ 6.8.1, and using the NI-Scope 1.6 drivers.
> I have LV 6.0 but haven't tried it.
> I built the code into an executable.
> I couldn't see any relevant BIOS setting; disabled power management.
> I stopped the taskbar updating the clock.
> I removed every program from StartUp.
> I stopped the network card & ejected it.
> I removed Windows automatic update, Microsoft Find Fast, & antivirus
> software.
> I used the simplest video driver that would work.
> I used msconfig to minimize the number of processes starting.
> I killed every task that I could find in the task list shown by
> ctrl-alt-del.
> I installed the Microsoft utility wintop; like Task Manager for Windows
> 9x it shows every program running, and I killed unnecessary ones.
> When the delay happens I don't see anything happening; the disk light
> doesn't flash.

> Look forward to your help!

> Thanks Mark



Mon, 02 Jun 2003 11:08:39 GMT  
 
 [ 2 post ] 

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