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I'm working on an application that uses multiple cameras. Until recently, its been with network cameras; now I'm trying to move this over to USB cameras. I'm aware of the limitations of USB2.0 bandwidth for this, so I just assumed that I could plug several USB2.0 cameras into a USB3.0 hub (which is then plugged into a USB3.0 port of course) and the streams from those USB2.0 cameras would then ride on the higher bandwidth USB3.0 interface...

This is not the case. Apparently, the USB3.0 connection uses different pins in the connector to isolate the two different interfaces, so if you have multiple USB2.0 devices plugged into a USB3.0 hub, they are still limited by the USB2.0 bandwidth.

So, is there any device/solution (like a USB2.0-to-USB3.0 converter) that will allow me to put a USB2.0 device onto the USB3.0 bus so that multiple USB2.0 devices can ride on the USB3.0 bus?

Ed.
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1 Answers1

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I don't think that there is any kind of the converter you mean. You need just to have camera with USB 3.0 device controller to use USB 3.0 bandwidth. When you use USB 3.0 host and USB 3.0 hub connected to it - you already use USB 3.0 bandwidth between them but when you connect USB 2.0 device to this hub - it will of course use only USB 2.0 bandwidth (between hub and device) and it will always be the bottleneck in this case.

user2699113
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  • Ok (been away for a while), with no "converter" gizmo available, I now have three usb3.0 cameras (logitech BRIO), and the problem is actually worse (hopefully I'm just doing something wrong)... With three BRIO cameras plugged into three different USB3.0 ports on my machine I find that I can't even use two cameras when configured at 640x360,MJPG. The second camera always comes back with error "No space left on device". I see from "lsusb" that they are on the 3.0 bus, but have no clue why I can't talk to all three of them. Is there some trick? – Ed. Nov 01 '17 at 12:34
  • Where did you get the error "no space left on device"? In system logs? What system do you use (linux/windows)?Maybe the driver doesn't allow to connect more than 1 camera at the same time (bad written driver)? – user2699113 Nov 02 '17 at 05:49
  • its the string-equivalent of the returned error code from opening the camera. There is no specific driver for this camera, it just comes up as a UVC device. Not knowing USB that deeply, my guess is that the camera (for some reason) tells the driver that it needs more bandwidth than it actually uses (basically hogging the pipe). This doesn't happen with other cameras. Seems to be specific to BRIO/Linux. – Ed. Nov 02 '17 at 11:04
  • I suppose that this camera as a USB device needs to have some USB driver which registers itself as a UVC device which in turn is accessible via V4L. Am I right? Now the usb device driver for logitech Brio can return ENOSPAC status in some circumstances which is (status ENOSPAC) transferred to your application. But this is my theory and I'm not sure in 100% percent about it. – user2699113 Nov 02 '17 at 12:33
  • As a UVC compliant device, I don't think it needs any special device driver in Linux; but I am not 100% sure about that. I've used several cameras from several vendors (all UVC compliant) and never had to deal with any device specific driver before. My guess is that this is specific to the BRIO. I will know if a few days, as I've ordered a few other USB3.0 cameras to test. I'll post the results. – Ed. Nov 04 '17 at 20:10
  • I was thinking a little about the UVC compliant devices and now I think that you may be right with it. I mean if USB camera present itself properly as a USB video device then linux kernel can serve appropriate API to it as UVC device. Anyway I'm interested in effects of your investigation. – user2699113 Nov 05 '17 at 12:57
  • It looks like this issue is specific to the BRIO; I now have a few other 3.0 cameras and I am able to easily put several of them on a single USB3.0 port and things work just fine (within the limits of the interface of course). – Ed. Dec 01 '17 at 21:55
  • Did you compare the device descriptors of both: BRIO and the new one cameras? Are there any differences for example in power requirements? – user2699113 Dec 08 '17 at 05:42