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C application using USB 6009 only works if NI Max is open


When running a simple C application using a USB 6009 device, a pulse is sent out on two digital lines, every 20 ms. The pulse length is 1 ms. The pulse is created by toggling the line high, waiting for a 1ms, and then setting it low.

The application works fine on a development computer using the latest NI drivers.


When running on another computer, using the same NI drivers, the application misses sending out about 20% of the pulses, and their length are no longer 1 ms, but more like 5 ms.


However, which is intriguing, if one opens the NI Max application, while running the C application, the pulse outputs becomes correct and behaves as on the development computer. 


Any ideas what can be causing this erratic behavior?



-Totte Karlsson

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