How do I know when the buffer flushed all the data out?

Question

I am using a very high sampling rate (500000 Hz) and acquire 1024 data points continuously.   It takes 370000 data points in 10 second.   I use a counter to help with the retrigger PFI line.   I have a huge buffer so that I can make sure that the buffer is not overflowed.  The code is attached below.  My problem is that the data acquisition is done so fast (in 10 seconds)  but the processing of the data is not.  In :nEvent, I basically save and plot the data.  The saving process is not slow.   However, our videocard is so SSSSLOOOW and can not keep up with realtime data display.    After the user is done collecting the data, they do not want to wait for the screen to plot the data from the buffer.   So after the data collection is done, I basically stop the plotting process but we still need to flush the data out from the buffer for saving.  My question is that how can I tell when the buffer is empty.
Thanks,
Yajai
m_task = std::auto_ptr<CNiDAQmxTask>(new CNiDAQmxTask("aiTask"));
m_counter = std::auto_ptr<CNiDAQmxTask>(new CNiDAQmxTask("coTask"));
m_task->Stream.Timeout = -1;
//Create a channel
m_task->AIChannels.CreateVoltageChannel(physicalChannel, "",
static_cast<DAQmxAITerminalConfiguration>(DAQmxAITerminalConfigurationRse), minimum, maximum,
DAQmxAIVoltageUnitsVolts);
m_task->Timing.ConfigureSampleClock(counterSource, sampleRate,DAQmxSampleClockActiveEdgeRising,DAQmxSampleQuantityModeContinuousSamples, samplesPerChannel);
m_task->Stream.Buffer.InputBufferSize = samplesPerChannel * 2000;
m_counter->COChannels.CreatePulseChannelFrequency(counterChannel, "coChannel", DAQmxCOPulseFrequencyUnitsHertz, DAQmxCOPulseIdleStateLow, 0, sampleRate, 0.5);
m_counter->Timing.ConfigureImplicit(DAQmxSampleQuantityModeFiniteSamples, samplesPerChannel);
m_task->Control(DAQmxTaskVerify);
m_counter->Control(DAQmxTaskVerify);
m_counter->Triggers.StartTrigger.ConfigureDigitalEdgeTrigger(
referenceTriggerSource, DAQmxDigitalEdgeStartTriggerEdgeRising);
m_counter->Triggers.StartTrigger.Retriggerable = true;
m_taskRunning = true;
m_counter->Start();
// Set up the graph
m_Graph.Plots.RemoveAll();
for (unsigned int i = 0; i < m_task->AIChannels.Count; i++)
m_Graph.Plots.Add();
m_Graph.Plots.Item(i+1).LineColor = m_colors[i % 8];
// Create Multi-channel Reader
m_reader = std::auto_ptr<CNiDAQmxAnalogMultiChannelReader>(new CNiDAQmxAnalogMultiChannelReader(m_task->Stream));
m_reader->InstallEventHandler(*this, OnEvent);
m_reader->ReadMultiSampleAsync(samplesPerChannel, m_data);

Answer 1

Yajai,
I'm a little confused about your acquisiton. Do you intend for it to be
finite, or continuous? I'm also unclear about your rates. You state
that you are acquiring 1024 samples at 500kHz, yet you get only 370k
samples in 10 seconds. Are you periodically acquiring 1024 samples at
500kHz?  Do you do any reads other than the final m_reader->ReadMultiSampleAsync(samplesPerChannel, m_data)? Could you provide the code where you stop the plotting process?
Thanks,
Ryan V.
Ryan Verret
Product Marketing Engineer
Signal Generators
National Instruments