Callbacks and number of acquired samples

[Mar1976]

Hi all,

in my application i need to acquire data through a pcie 6323 with C# .Net.

For my purpose when i start the software the NI card is configured to acquire data in continuoussample mode.

After user acts on main form and press start button, i call again 

analogInputTask.Timing.ConfigureSampleClock(
ClockSource
, SampleRate
, ActiveEdge
, SampleMode  // starts in continuous  samples to switch to finite samples when acting on main form
, samplesPerChannel);

with samplemode = finitesamples

The callback i use to call through  following lines of code:

 this.analogInputAsyncResult =
this.analogReader.BeginReadWaveform(
SamplesPerChannel
, analogInputReaderCallback
, analogInputTask
);

 is this: 

private void AnalogInCallback(IAsyncResult ar)
        {
            try
            {
                if (runningAnalogInputTask != null && runningAnalogInputTask == ar.AsyncState)
                {
                    /// Handles the end of an asynchronous read initiated with 
                    /// BeginReadWaveform and retrieves the read samples.
                    /// REMARKS
                    /// If you call EndReadWaveform before the asynchronous read 
                    /// represented by the provided IAsyncResult is complete, 
                    /// EndReadWaveform waits for the read to complete before returning.
                    analogInputReaderData = analogReader.EndReadWaveform(ar);

                    try
                    {
                        double[] buffer = new double[SamplesPerChannel];
                        DateTime[] dtBuffer = new DateTime[SamplesPerChannel];

                        using (TimedLock.Lock(AnalogInputs))
                        {
                            if (analogInputReaderData != null && analogInputReaderData.Length > 0)
                            {
                                try
                                {
                                    foreach (SampleBuffer<double> input in AnalogInputs)
                                    {

                                        var inputData =
                                            analogInputReaderData
                                            .Where<AnalogWaveform<double>>(r => r.ChannelName.Equals(input.Name))
                                            .Single();

                                        /// Read samples
                                        inputData.GetBuffer(true).CopyTo(buffer, 0);

                                        input.AddSamples(buffer);

                                        /// Read timestamps
                                        inputData.GetTimeStampBuffer().CopyTo(dtBuffer, 0);

                                        input.AddTimeStamps(dtBuffer.Select(dt => dt.Ticks));
                                    }

                                    OnSampleBufferChanged(new SampleBufferChangedEventArgs(AnalogInputs));
                                }
                                catch (Exception ex)
                                {
                                    Debug.WriteLine(ex.Message);
                                }
                            }
                        }
                    }
                    catch (LockTimeoutException) { }

                    /// Restart reading
                    analogReader.BeginMemoryOptimizedReadWaveform(
                          SamplesPerChannel
                        , analogInputReaderCallback
                        , analogInputTask
                        , analogInputReaderData
                        );

                }
            }
            catch (DaqException ex)
            {

#if DEBUG
                Debug.WriteLine(ex.Message);
#endif
                runningAnalogInputTask = null;
                analogInputTask.Dispose();
            }
        }

i'd like to ask you if with the check i do with

if (analogInputReaderData != null && analogInputReaderData.Length > 0)

is correct to see if there is incoming acquired samples. What i mean is that when i switch to finitesamples the callback is the same so before the trigger starts i want to not perform any processing on the acquired data premise that there is a way to check that buffer is empty 'cause the trigger is not yet started.

Thanks in advance

[nyc_(is_out_of_here)]

Consider looking at the C# examples that should have been installed during your installation of NI-DAQmx.

[Mar1976]

Sure, but it would be better if some NI expert share with me some link with deep explanation of this.

Also when i've tried to modify the code to understand it better i've noticed that callback is called also when board is in finite sample mode and trigger is not yet detected.

Now instead the callback in the same situation is called only if trigger is detected