Re : Strange lattency while communicating with 2 device by USB

[Pavel_47]

Hello,

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.

Pavel

[Pavel_47]

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)

[Pavel_47]

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.

Thanks