Tried a bunch of examples, DAQ Assistant code, mega-research time. At the end of the road.This is pretty much my first go at DAQmx programming after years of Traditional DAQ programming followed by a long hiatus.
I'm using an IEPE force hammer hit to start sampling from a USB-4431. I'm going to be post-processing fft; I want ten seconds of data at 4096 samples per second (40960 samples).
As I'm acquiring data, I want to update a graph to show the buffer contents, adding data to the graph every 125 mS until the end of the 10 second capture. The trigger, data sampling start, and acquisition is working fine. The problem is getting it to the graph control.
The graph gets updated in inconsistent fits and spurts. The entire 10 second shot eventually makes it to the graph, but it takes anywhere from 30 to 120 seconds to display, sometimes in rapid "chunks" with long pauses. Sometimes the initial trigger data gets displayed right away, and sometimes it takes 15 seconds just to display the first 512 samples!
I've obviously got something fundamentally wrong here. Could someone please have a look at the code below for me. TIA~!
void main (void)
{
X_AxisIndex = 0;
NumDataPoints = 512; // At a sample rate of 4096 samples/second, trying to update the graph every 125 milliseconds.
CreateDaqTask();
DAQmxStartTask(taskHandle);
RunUserInterface();
} // Main
void CreateDaqTask(void)
{
// *** All this works fine AFAIK ***
DAQmxCreateTask("",&taskHandle);
DAQmxCreateAIForceIEPEChan (taskHandle, "Dev1/ai0", "Hammer", DAQmx_Val_PseudoDiff, -10, 100, DAQmx_Val_Pounds, 50.0, DAQmx_Val_mVoltsPerPound, DAQmx_Val_Internal, 0.0021, NULL);
DAQmxSetChanAttribute(taskHandle, "Hammer", DAQmx_AI_Coupling, DAQmx_Val_AC);
DAQmxCfgSampClkTiming (taskHandle, "OnboardClock", 4096, DAQmx_Val_Rising, DAQmx_Val_FiniteSamps, 40960); // Grab 10 seconds worth of data at 4096 samples per second.
DAQmxCfgAnlgEdgeStartTrig (taskHandle, "Hammer", DAQmx_Val_RisingSlope, TriggerLevel);
// *** All this works fine AFAIK ***
// Here the idea is to fire a callback every 512 samples/4096 samples per second = 125 mS so I can display the data to a graph control, updating it every 1/8th of a second.
DAQmxRegisterEveryNSamplesEvent (taskHandle, DAQmx_Val_Acquired_Into_Buffer, NumDataPoints, 0, EveryNCallback, NULL);
} // CreateDaqTask
int32 CVICALLBACK EveryNCallback(TaskHandle taskHandle, int32 everyNsamplesEventType, uInt32 nSamples, void *callbackData)
{
// Read the 512 data points and display them.
DAQmxReadAnalogF64 (taskHandle, NumDataPoints, 15.0, DAQmx_Val_GroupByChannel, Buffer, NumDataPoints, &CurrentBufferIndex, NULL);
PlotWaveform (MainPanel, Main_Graph, Buffer, NumDataPoints, VAL_DOUBLE, 1.0, 0.0, X_AxisIndex, 1.0, VAL_THIN_LINE, VAL_NO_POINT, VAL_SOLID, 1, VAL_YELLOW);
X_AxisIndex += NumDataPoints;
return 0;
} // EveryNCallback
