Quote from: alh on February 03, 2015, 12:13:54 AM

Regardless of the mining software, you will want the U1/U2 on a powered hub.

I have a raspberry Pi B+ and 4 U1/2s. Three U2s are connected to a powered hub and the U1 is connected to one of the RPi USB ports.
There is a configuration change to allow the Pi ports to source 1.2A I recollect. That suggest it may be possible to have 2 U2s connected directly - but I have not tried it.
My USB(2) hub is crap - with 3 antminers connected it drops a lot of volts - I think I'm feeding it with 5.7V to get 4.5V at the USB device.

With a B+ or the new Raspberry Pi 2 it might be possible to connect 2 U2s directly - but no more.