Synchroniz​ation of M-Series cards via RTSI and ANSI C?

Question

Hi!
This is my first post and I'm happy to be here. I tried to search as thoroughly as possible, but if this has been answered elsewhere, I'd be grateful for a hint/link nevertheless.
System:
Win 2000 Pro with NI-DAQmx (part of NI-DAQ 7)
2x PCI-6220M, 1x PCI-6221M
RTSI Cable
all components are registered in MAX
Problem:
I want to synchronize the cards over the RTSI bus. I am using the ANSI C library. There's an example SharedClk10-FiniteAcq_main.c, but it is designed for PXI and uses the undocumented (at least in the C reference?) DAQmxSetTimingAttribute function. I tried to pass '/Dev1/RTSI7' as the clock source, but it did not work.
Then, after reading the C reference a bit more, it seemed as if I needed to use DAQmxExportSignal. But it gives me an error DAQmxErrorInvalidRoutingSourceTerminalName_Routing = -89120 when I try to route DAQmx_Val_20MHzTimebaseClock to '/Dev1/RTSI7'
I'd like to know what C functions I have to call in which order to enable synchronized sampling with the three M-Series cards.
So far I do:
DAQmxCreateTask (primary & driven)
DAQmxCreateAIVoltageChan (p & d)
DAQmxExportSignal (p)
DAQmxCfgDigEdgeStartTrig (d - trying to import the failed export of /Dev1/RTSI7)
DAQmxStartTask (d & p)
DAQmxReadAnalogF64 (p & d)
DAQmxStopTask(p & d)
This is my first time using M-Cards or the ANSI C functions, so I might have missed something essential.
Can anyone give a hint as to what I need to do?
Jens

Answer 1

First, if you haven't, you should explicitly create a RTSI cable in MAX. This can be done by right-clicking on Devices and Interfaces -> NI-DAQmx Devices and choosing Create New NI-DAQmx Device -> RTSI Cable. Then, for each device that is connected to the RTSI cable, use MAX to edit its properties and in the "RTSI Configuration" tab, specify the RTSI cable. This will allow NI-DAQmx to automatically route signals of the RTSI cable.
Now that a RTSI cable is configured, you don't need to explicitly export signals from the task. You can use the DAQmxGetMasterTimebaseSrc function to retrieve the master timebase terminal name from the primary task and the DAQmxSetMasterTimebaseSrc function to set the master timebase terminal name for the driven task. The DAQmxGetMasterTimebaseRate and DAQmxSetMasterTimebaseRate functions can be used in a similar manner. Configuring these properties will result in NI-DAQmx automatically routing the master timebase signal from the primary task to the driven task using the RTSI cable. To ensure the driven device starts at the same time, invoke the DAQmsxCfgDigEdgeStartTrip function passing a triggerSource parameter of "/ai/StartTrigger" which will result in NI-DAQmx automatically exporting the start trigger signal for the primary task over the RTSI bus and using it as a digital start trigger for the driven task.
I assume that you will also want to invoke the DAQmxCfgSampClkTiming function for each task to specify the acquisition rate and number of samples to acquire. Note that since the master timebase signal and the start trigger signal are already routed using the RTSI cable, the sample clock itself does not need to be shared between the two tasks.
geoff
Geoffrey Schmit
Fermi National Accelerator Laborary