Getting error -200479 on 3 card PXI 6071E synchronized system

Question

I am trying to synchronize 3 PXI6071 boards, each having multiple channels, so that they are on the same timebase and can be started with the same trigger. I have written a vi to do this . It works fine when I have only one channel on each of the three cards or when I have the master card scanning multiple channels and the other two cards only using one. When I have the second and/or third card scan multiple channels, I get the -200479 error on the DAQmx start task for one or more of the cards. The card(s) that don't through the error seem to work fine. I've attached the vi and a subvi I wrote.
Attachments:
Multi-Device_Synch_-_Shared_Timebase_&_Ext_Dig_Trigger_altered_with_subvi ‏287 KB

Answer 1

The problem is in your Create multichannel DAQ task VI. Inside of this VI, you are only creating a task and channels if it's the first time the VI has been run. However, you are calling this VI twice from your main VI. Things will work fine the first time you call the VI, but the second time it's called for the second task, the creation of your task and channels will be skipped. Since the task in this sub VI is part of a shift register, it will retain the value from the last time it was run. This means you will have the same task ID for both of your tasks. If you put an indicator on the task out variable of your Create multichannel DAQ task VI, you'll see that they are in fact using the same task ID. This means when you are configuring the timing and tri
ggering properties the second time around, you are actually overwriting the settings made from the first task and you finally get an error the second time the Start VI is called on that task. You can modify your application code so this doesn't happen, but the easiest way to fix this is to make the Create multichanel DAQ task VI reentrant. To do this, go to the VI Properties in the File menu. Choose the Execution category from the drop down list at the top of the window and check the Reentrant execution check box.