Thursday, August 22, 2013

USB3 Vision Clarification

If you read the Comments my ramblings sometimes attract you’ll see that “USB3 Vision versus GigE Vision” drew some questions. As the writers took the time to read what I had to say I’d like to pay them the courtesy of a reply.

First off, I should have cited my sources. Most of my information came from the Basler paper referenced in “Understanding USB3 Vision” although I did pick up a few other points from Stemmer and others. Regrettably, I didn’t save the links but if you Google “Advantages of USB3” or some similar phrase you’ll find the pages I used. Lesson learned.

And now, to the questions (or should that be answers?):

  • Regarding USB3 cable length – yes I’m sure you can use repeaters but everything I’ve seen says the effective limit is around 3m.
  • On cable security – I meant the provision of screw-in connectors, but I also included immunity to noise. It’s my understanding that USB3 cables offer superior construction in this regard.
  • On how I calculated the CPU load scores for USB and GigE – confession time – I didn’t calculate anything. It was a subjective assessment again based on what I read in the Basler paper. In my defense, my intention was to highlight relative strengths and weaknesses rather than assign absolute scores, and I think I accomplished that.

If anyone has any different information that runs counter to what I’ve said, I’d be glad to hear from them.

1 comment:

Vincent Rowley said...

Dear Brian,

I like these posts. Here are some comments.

With respect to cable length, I believe that it is correct that the reach is limited to 3-5 m for regular passive cables. Cable reach can be extended with active cables.

Regarding CPU utilization, I think a way to look at this is that USB uses DMA which means that drivers manufacturers have to play less tricks to get a high performance system. For the users, this means that chances are that various SW implementations would be able to achieve more or less the same level of CPU utilization.

In my view, the main advantage of USB 3.0 versus GigE Vision is the throughput. With USB 3.0 you can get ~3x the bandwidth from a camera of the same size of a GigE Vision camera. GigE Vision obviously supports 10 Gbps but I do not know one that can fit it in a 30x30x30 mm device. On the other hand, it is easier to share video with GigE Vision and intrinsic cable length is higher.

The main advantage of UBS 3.0 over Camera Link would be a lower system cost i.e. no frame grabber required. I have a feeling that USB 3.0 will steal Camera Link market shares.

Vincent Rowley