[clug] Single Board Computer with two OTG USB interfaces. Suggestions?

steve jenkin sjenkin at canb.auug.org.au
Thu Mar 9 09:33:42 UTC 2017

I’m looking at playing with “protocol breaks” and wanted a cheap ARM computer that had two USB OTG ports so I could connect two computers via one USB Host port on each.

I can’t use Ethernet, as IP over Ethernet is the protocol I’m ‘breaking’ (not forwarding directly).
I could use IP over serial, but that fails as well: there’s no break in the protocol.

I might be able to find a robust, well tested non-IP serial protocol, but most devices only push to 115kbps, which seems a little slow.
I’d like higher than 1Mbps.
I looked at the native bus on some of the popular SBC’s, but all the solutions I saw used ‘bit banging’ by the main CPU, leaving no cycles over to do any other work. USB controllers offload the link layer work.

I don’t want to design & build a USB switch to share a single OTG port between two hosts.
If someone knows of a ‘shield’ or ‘cape' that does this, or a standalone circuit board that can be controlled by digital lines, assembled or not, that’d work for me, kinda sorta, but is not my first choice.

The Raspberry Pi model A has one OTG port from my reading, not enough to simultaneously connect to two computers.
I could buy two USB-Host to USB-OTG adaptors, but haven’t found any that are ~$5. [If you know of one, that’s a solution]

The ~US$49 Beaglebone Black has ethernet, one OTG or USB Client and one USB 2.0 Host port.

I’m not sure of the specs of BeagleBone boards.
this page suggests a single OTG port. It also uses ‘USB 2.0 Client’ for some models, which may be the same, or not.


More info about “Protocol Break” is buried in this Wikipedia article:

Steve Jenkin, IT Systems and Design 
0412 786 915 (+61 412 786 915)
PO Box 48, Kippax ACT 2615, AUSTRALIA

mailto:sjenkin at canb.auug.org.au http://members.tip.net.au/~sjenkin

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