Start multiple analog input tasks simultaneously using DAQmx C API

[MisplacedPouch]

I need to synchronize the start of 8 analog input tasks using DAQmx C API.

TaskHandle* task_handles = new TaskHandle[8];
float64 sample_size = 40000;
float64 rate = sample_size * 100;
for (int i = 0; i < 8; ++i) {
  // initialize task
  DAQmxCreateTask("", &task_handles[i]);
  std::stringstream resource_name;
  resource_name << "PXI1Slot1" << i << "/ai0:3";
  DAQmxCreateAIVoltageChan(task_handles[i], resource_name.str().c_str(), "",
                           DAQmx_Val_Cfg_Default, -1.0, 1.0, DAQmx_Val_Volts,
                           NULL);

  // configure task details
  DAQmxCfgDigEdgeStartTrig(task_handles[i], "What trigger should I use?",
                           DAQmx_Val_Rising);
  DAQmxCfgSampClkTiming(task_handles[i], "OnboardClock", rate, DAQmx_Val_Rising,
                        DAQmx_Val_ContSamps, sample_size);
  DAQmxRegisterEveryNSamplesEvent(task_handles[i],
                                  DAQmx_Val_Acquired_Into_Buffer, sample_size,
                                  0, EveryNCallback, this);
}

// start tasks
for (int i = 0; i < 8; ++i) {
  DAQmxStartTask(task_handles[i]);
}

I tried to set a start trigger for the 8 tasks but I could not identify the correct trigger:

http://zone.ni.com/reference/en-XX/help/370466V-01/mxcncpts/termnames/

For example, PFI0 is not what I need because I do not intend an external source for synchronization.

I know this is a rather simple question, but how can I start the 8 tasks simultaneously?

You may suggest me to combine the 8 input tasks into a single task. I have tried it. It works but the data acquisition becomes incredibly slow. So let's assume that the merging of tasks is not an option.

[JKarma]

Hello MisplacedPouch,

Which hardware are you using? 

[MisplacedPouch]

I am using eight PXIe-6124 modules connected to a PXI Chassis PXIe-1075.

[MisplacedPouch]

After going through many kinds of documentation, I have finally figured out a fix.

The solution is to export the StartTrigger of any one task using DAQmxExportSignal.

Then all the other tasks should be configured to start upon the exported signal using DAQmxCfgDigEdgeStartTrig.

I will post a more detailed version of the solution later.

[Kevin_Price]

---

The solution is to export the StartTrigger of any one task using DAQmxExportSignal.

Then all the other tasks should be configured to start upon the exported signal using DAQmxCfgDigEdgeStartTrig.

Yes, *AND* make sure the task that exports is the one you start *last*.  That way all the others are running and waiting for the trigger signal when it asserts.

-Kevin P