USB hardware config/question

HI all,
I just wanted to clarify how USB hardware should be configured.
If the BeagleBoard itself is powered from a power-supply, is it
reliable to use a non-powered USB hub? Or is it always 'best' to use
a powered USB hub?

(In my current set-up I have the Beagle powered by a power-supply,
and: unpowered hub, USB mouse and USB keyboard. Sometimes the
keyboard stops responding but it's not entirely clear why.)

Thanks in advance,



You should still use a powered usb hub. The OTG USB port on the beagle
board only have to deliver 100 mA instead of the usual 500 mA for
regular USB ports, if recall correctly.



I think you need a self-powered hub, i.e., one with an external power
supply. The BeagleBoard USB OTG port can only source 100mA of USB
power which is typically enough for a keyboard or a mouse or a hub,
but not all three for reliable operation. See
for more details on USB OTG.

The fact that your keyboard stopping responding is a classic symptom
of inadequate USB power. What's probably happening is that the
BeagleBoard has just barely enough current to power your USB devices,
but if voltage drops slightly because the processor gets extra busy
(for example), the USB controller thinks there is not enough power
available and starts dropping devices.

I has a similar problem when I got started where the keyboard worked
fine but the mouse didn't. The Ångström console showed the USB
controller continually trying to add the mouse and deleting it because
there wasn't enough power. Adding external power to the hub fixed the
problem immediately.


If you use the OTG port as a host, you must use a powered hub. The OTG support only supplies around 100mA.