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

[Bob Edwards]

On 09/03/17 20:33, steve jenkin wrote:
> 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.
>

Hi Steve,

I am not aware of devices that are both "cheap" and have two OTG ports.

A "cheap" solution might be to use two embedded devices, each with an
OTG port and then use the ethernet port (or the serial port) to actually
transfer the data (in only one direction!) between them.

Serial would be better, as you can physically disconnect the reverse
channel, and you don't need all the IP layers - it's only the data that
you need to move back and forth. But, as you say, the speed would be
limited.

> I don’t want to design & build a USB switch to share a single OTG port between two hosts.

That wouldn't work in any case - USB is a one host (master), multiple
device protocol. This suggestion implies that two masters can both
connect to the same USB device at the same time - the protocol
specifically doesn't allow that.

cheers,

Bob Edwards.

> 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.
> <http://beagleboard.org/boards>
>
> ===============
>
> More info about “Protocol Break” is buried in this Wikipedia article:
> <https://en.wikipedia.org/wiki/Unidirectional_network>
>
> --
> 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
>
>