[GTALUG] USB "gadget" on Raspberry Pi 4; Tiny Pilot KVM

[Lennart Sorensen]

On Mon, May 10, 2021 at 03:29:11PM -0400, D. Hugh Redelmeier via talk wrote:
> It's hard to find general-purpose computers that can be USB clients, 
> rather that hosts.  This mode is called "gadget".
> 
> You can do this with a Raspberry Pi Zero.
> 
> You can also do it with a Pi 4!
> 
> It turns out that the Pi 4's power connector is also a USB 2.0 port.
> To conveniently access it, you can use one of these:
> 
> <https://www.buyapi.ca/product/usb-c-pwr-splitter/>
> (There's a different splitter that might be aimed at the Pi Zero)
> 
> Why you cannot do this with other models of Pi:  The Broadcom chip has one 
> USB port.  It is fed to a USB hub, and that's exposed on the connectors.  
> A USB hub cannot provide Gadget ports.
> 
> On the Pi 4, the Broadcom's USB port is connected to the power input, with 
> no hub in the way.
> 
> | From: Stewart C. Russell via talk <talk at gtalug.org>
> 
> | Buyapi (in Nepean) and Canakit are Canadian official
> | resellers, so are supposed to get priority on stock. Practically,
> | they'll run out like everyone else from time to time.
> 
> If I were making a buyapi order, I'd certainly throw in a splitter.  Just 
> on spec.
> 
> 
> What prompted me to look at this is the description of the "TinyPilot" KVM 
> project.
> 
> <https://tinypilotkvm.com/>
> <https://www.servethehome.com/tinypilot-voyager-kvm-raspberry-pi-remote/>
> 
> This is a Raspberry Pi 4 + extras that acts as another computer's 
> Keyboard, Video, an Mouse.  It can be accessed via ethernet.  Not cheap 
> enough for me.
> 
> Their magic sauce is software (there is an open source subset),
> a splitter for the USB C power-in (like above, but US$35), and an HDMI 
> capture circuit (AliExpress dongle for less that $20 should work).
> 
> According to STH, the obvious competitor is the Lantronix Spider.
> The cheapest, used, on ebay is over $200 and may not have the features I'd 
> like.
> 
> I actually use 4-port UltraHD KVMs that I got for about $100 (in other 
> words, $25/computer).  They fulfill my needs at a lower cost.  Maybe a Pi 
> Zero solution could cost about that.
> 
> The HDMI capture dongles are diverse and mysterious to me.  AliExpress's 
> descriptions are unreliable.  For example, the first item in their list 
> was emblazoned with "4K" but the specs said 1080p was the max resolution.  
> Any recommendations?
> 
> - I think FullHD is fine.
> 
> - USB 3.0 might be an advantage: higher bandwidth possible
> 
> - "driverless" would be nice.  I think that that means it looks like a 
>   USB video camera the software.
> 
> AliExpress is an adventure.  I would not bother if I actually had a 
> serious or 
> urgent need.

Pretty sure the beaglebone can do usb gadget mode.  In fact I think it
has to since I believe that is how it implements the serial console as
well as storage and networking if desired.

Doing video, not sure.  I am pretty sure I once saw an HDMI switch that
attached to a raspberry pi to control it, but I can't seem to find it.

-- 
Len Sorensen