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Strange lattency while communicating with 2 device by USB



Here are keypoints of my setup:

  • 1st USB port: NI USB-6343
    • 3 analog outputs are emloyed
    • 1 analog input is employed
    • loop_A delay: 100ms
  • 2nd USB port: digital camera
    • input data: 2 consequtive images (180x180 pixels, 2 bytes per pixel)
    • loop delay B: 200ms
    • on each loop iteration of loop_B, 2 images are sent to loop_A (using queue)

Sometimes this functionnality is perurbed by unexplained latency. Here is statistics of loop_A delay (delay is added into listbox if delay is superior to 1 sec).



Other observation: once such lattency happens, the LED "Active" on USB-6343 is almost OFF.


Thanks in advance.



Message 1 of 3

Probably cause of such malfunction could by desynchronization of loop_A and loop_B that run in separated VIs.

Anyway how to explain such huge latency ... more than 5 sec, i.e. more than 50 times of the loop delay (100 ms)

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Message 2 of 3

Resolved. The problem was low-power USB that powered digital camera.

Once camera put on external Power, the problem disappeared.

One more question before closing this topic: is there some function in LabVIEW for determining whether USB port is powerful or not.


Message 3 of 3