USB keyboard udev rule

Robin Paulson robin.paulson at
Tue Nov 11 00:52:14 CET 2008

2008/11/11 Alastair Johnson <alastair at>:
> Pander wrote:
>> Does anyone have a udev rule for USB keyboard that does the following.
>> When no external USB devices are connected and a keyboard is plugged in,
>> USB can switch to host mode and switch back when USB keyboard is
>> unplugged. As far as I'm concerned, this would be a very welcome feature.
> AFAIK we don't have a means of autodetecting whether we should be host
> or device, and if we aren't in host mode we can't detect the keyboard
> insertion. There may be a way of doing this using the ID pin but I don't
> know how standard it would be.

would there be any adverse consequences to the neo always assuming
it's in host mode (and thus supplying power also), unless a voltage is
detected? i.e. as soon as any power disappears, it automatically
switches back to device again?

from what i can tell from previous discussions, being provided with
power while supplying it, doesn't damage the neo, as it automatically
turns off the power when this happens

i'm not thinking just about keyboards here, but more about 'faking' a
usb otg port, or at least something similar

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