Hi
I have a 6602 card where each of 5 counters are hooked up to measure pulsewidts on their inputs.
Each task has the same timeout.
After createing the task and corresponding counter readers and AsyncCallbacks I start an async read of 10 samples on each task.
Now to may problem. If I start these async reads right after eachother like
reader1.BeginReadMultiSampleDouble(10, ACallback, null);
reader2.BeginReadMultiSampleDouble(10, ACallback2, null);
When there is no pulsewidths to measure the async read has a timeout. At that point I receive the following Exception in the callback
System.AccessViolationException: Attempted to read or write protected memory. This is often an indication that other memory is corrupt.
at NationalInstruments.DAQmx.Internal.DaqAsyncResult.ThrowAsyncException()
at NationalInstruments.DAQmx.Internal.CounterMultiSampleDoubleReadAsyncResult.End()
at NationalInstruments.DAQmx.Internal.CounterReaderImpl.EndReadMultiSampleDouble(IAsyncResult asyncResult)
at NationalInstruments.DAQmx.CounterReader.EndReadMultiSampleDouble(IAsyncResult asyncResult)
at AR4000_Test.IO.DataAcquisitionBase.ReadPulseWidthCallback(IAsyncResult ar) in C:\Users\joj\Documents\Visual Studio 2008\TestProjects\AR4000 Test\AR4000 Test\IO\DataAcquisitionBase.cs:line 78
If I insert a delay of 20ms, so timeouts will occurr 20ms apart I do not receive the exception.
reader1.BeginReadMultiSampleDouble(10, ACallback, null);
Thread.Sleep(20);
reader2.BeginReadMultiSampleDouble(10, ACallback2, null);
This is clearly not a solution since I cannot be sure that timeouts later will drift towards eachother causing the same exception.
I can also catch the exception and continue, but since I do not know what causes the Exception I rather not just eat it and continue.
Why is this happening and what can I do to prevent it.
BR
Jonas
