Is a VI execution timing dependant on the OS processing, in a timing critical application?

[Shoab]

I am trying to distribute a Labview/Teststand application, that a previous employee had developed, on a new machine. This is using LV7.1 and TS3.1. The application works well on the previous PC (XPSP2), but certain tests fail on the new PC (also XPSP2), and it seems that somehow it is timing related. Certain signals not executing in the correct time frame.

Could using two (phisycally differect) DAQ cards of the same type produce different timing outputs? I am using PCI-DIO-96 and PCI-6025E cards in both the PCs.

In some of the tests, the VI is running an SPI bus, which is timing critical. The VI uses "Wait" to time the various signals from one sequence frame to another. Is there any other method to control the sequential execution of the frame in a more controlled manner?

Is the block execution within a VI independant of any OS delays? If multiple VI's are used and each one is interdependant on each other, is that a good code writing practice? I think if all the timing critical logic is placed under one VI, it might help.

Are there any pitfalls that one needs to be careful of, when designing VI's for applications that are timing critical?

Shoab

[TCPlomp]

In short:
Yes

In Long:
Yes

You are correct that using "wait ms.vi" is a bad way to sync to systems. IN LV 7 you have the timed loop. This can be used to start loops at the right time. If you consider upgrading to 8 you can use the timed sequence that should better suite your needs.
If I am correct you can correlate both IO-cards with an extra cable for precision timing (us or so)

Ton

[Dennis_Knutson]

You also might want to consider the USB-8451 for SPI communication.

[unclebump]

Take a look at task manager and see what processes are running on both computers. Do they have the same amount of memory??

If it is that critical, maybe you should be using RT.

This helped me on a win2000 system.

[link removed]

Message Edited by unclebump on 10-27-2006 06:38 PM