01-23-2007 08:22 AM
01-23-2007 08:51 AM - edited 01-23-2007 08:51 AM
Message Edited by Jochen on 01-23-2007 03:55 PM
08-13-2012 10:42 AM
Is there any way I can check it by myself by writing some example code? I couldn't find an example code to do this. I am using USB 6341.
08-17-2012 04:21 AM
Hi Rafii,
measuring bus latency is not a simple task and I don't think you can accomplish this without low-level debugging tools.
With only the 6341 in place you could try to measure the overall system latency which also includes all associated driver layers and buffers.
In general bus latency is not a problem for streaming applications and it doesn't lower the data throughput. For any type of single point closed loop application (e. g. acquire a voltage value - calculate a control algorithm - output a voltage value) bus latencies are limiting factors for both, control loop frequencies and deterministic behavior.
Regards,
Jochen
04-01-2013 11:47 AM
Hi Jochen,
The figure is very informative. Thanks for sharing. Could you also share the source of this figure? I'm curious how the measurements were done and how the latency were defined. Thank you.
04-01-2013 03:06 PM - edited 04-01-2013 03:07 PM
I don't know if the figure is in this video, but it does discuss and compare various busses if I recall:
https://ni.adobeconnect.com/_a56821929/p21882777/?launcher=false&fcsContent=true&pbMode=normal
-AK2DM
Not sure if that link will work, just noted it has a https connection. Let me know.
Edit- The Figure appears at time index of 5:22.
04-01-2013 03:16 PM - edited 04-01-2013 03:17 PM
Here's a link to the webcast in case my original one wouldn't work:
http://zone.ni.com/wv/app/doc/p/id/wv-183
And here is the white paper:
http://www.ni.com/white-paper/3509/en
Note that these do not cover the newer USB 3,0 and the x8 and x16 PCI variants.
-AK2DM
04-01-2013 05:15 PM
Thank you! The paper and the vedio do give more details. But they don't explain how these data were acquired, whether they were based on measurements or theoratically calculated. I'm especially curious in the latency of USB 2.0. The 125 us latency of USB 2.0 seems to be related to the size of a microframe, which is also 125 us. But the latency of a bulk transfer will be restricted by the size of microframe. Could you explain the latencyof USB 2.0 in more detail? Thank you.