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PostPosted: Mon Feb 08, 2016 1:47 pm 

Joined: Mon Feb 08, 2016 1:43 pm
Posts: 2
I have a 7 slot USB3 hub that is plugged into a USB3 port on my PC. If I plug 6 cameras into the hub will that be adequate for the 6 cameras? If not, if I get another USB3 hub and connect it to a second USB3 port, will that work?


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PostPosted: Tue Feb 09, 2016 12:56 am 
iPi Soft

Joined: Wed Jan 11, 2012 6:12 am
Posts: 1934
Location: Moscow, Russia
USB hubs do not increase bandwidth or add USB controllers, they just add ports. Thus if those 2 USB 3.0 ports belong to the same USB 3.0 controller, they usually can only handle 2 PS Eye cameras at 60 fps. If this is an USB 2.0/3.0 controller in modern Intel chipsets (8x + series), it may handle up to 4 cameras AFAIK.


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PostPosted: Tue Feb 09, 2016 8:13 am 

Joined: Mon Feb 08, 2016 1:43 pm
Posts: 2
When you say 60fps, do you mean 640x480 or 320x240? The reason I ask is that at 640x480x60x24bits per color, it comes very close to the absolute bandwidth limit of usb 2.0. I wonder if that can be achieved with any usb 2.0 controller. If that can be done, then I might think that the 3.0 hub could handle the bandwidth of 6 of these guys. At 6x640x240x60x24 you get about half of the putative bandwidth of usb3. That is right at the limit of what I think the actual bandwidth of 3.0 controllers measure up. So your estimate of up to 4 each is probably about right. I am going to try that out with the recorder and see at what point do I start dropping frames.


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PostPosted: Wed Feb 10, 2016 10:46 am 
iPi Soft

Joined: Wed Jan 11, 2012 6:12 am
Posts: 1934
Location: Moscow, Russia
I mean 640x480@60 (max PS Eye mode). FYI, PS Eye transmits picture in Bayer encoding, not RGB. That requires 3 times less bandwidth than 24bpp RGB.
The limit of 2 cameras per USB 2.0 controller comes from practice rather than theoretical calculations of bandwidth.
Most of pure USB 3.0 controllers work with USB 2.0 devices (which PS Eye is) in compatibility mode that does not allow to utilize USB 3.0 increased bandwidth. So there is no difference from USB 2.0 controllers. Combined USB 2.0/3.0 controllers in modern Intel chipsets provide sufficient bandwidth for 4 PS Eye cameras according to our tests.


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