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Using LabWindows/CVI on a PC-104 Form Factor PC

Primary Software: LabWindows/CVI Development Systems>>Base Package
Primary Software Version: 8.1
Primary Software Fixed Version: 8.1
Secondary Software: N/A

Problem:
I am running a LabWindows/CVI application on a PC-104 form factor system running Windows. I have noticed that the CPU ramps up to 100% when running my application, even if my application isn't doing anything computationally intensive. Why is this happening and how do I fix this?

Solution:
Certain PC-104 devices have hardware defects that cause the QueryPerformanceCounter Windows SDK function to behave incorrectly. This function is used internally by LabWindows/CVI for processing messages. This bug can cause LabWindows/CVI to process messages inefficiently and therefore start fully utilizing the CPU.

This behavior can occur when running the LabWindows/CVI IDE on the machine as well.

The workaround is configure LabWindows/CVI to not use QueryPerformanceCounter internally via modifying the registry.

To disable this for the LabWindows/CVI Run-Time Engine (you will need to do this if you deploy any application on this device), you will need to add a string key called useDefaultTimer under HKEY_LOCAL_MACHINE\SOFTWARE\National Instruments\CVI Run-Time Engine\cvirte . The value has to be set to true.

If you are using the LabWindows/CVI IDE on the device, you can disable the performance counter by adding the same key and value under HKEY_LOCAL_MACHINE\SOFTWARE\National Instruments\CVI\[version] and then restarting LabWindows/CVI.

Refer to the Microsoft KnowledgeBase below to see if you are using the hardware with this defect.

Related Links:
Microsoft KB Q274323: Performance counter value may unexpectedly leap forward

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Report Date: 03/21/2007
Last Updated: 03/27/2007
Document ID: 47KEK05B

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