Quote from cjrhoades on December 12, 2011, 00:17
Also, I'm wondering if this is possible:
Is there any technical information on the LapDock, like a schematic?
Otherwise, here's my SWAG. Normally, you connect a USB keyboard and mouse to USB host ports, which supply power to the keyboard and mouse. If there's only one USB host port, it supplies power to a hub which then powers the keyboard and mouse. The LapDock is a little different: it must include a hub so the Atrix can talk to the LapDock's keyboard and mouse, but the LapDock's internal hub also provides upstream power to the Atrix which is the opposite of a normal upstream port. But that's OK, since both devices are made by Motorola.
Most likely what you'd need for RasPi is to make a custom cable that takes the LapDock's power signals and sends them to RasPi's power input, and takes the data twisted pair and sends it to one of RasPi's USB host ports.
If my SWAG is correct, this should work electrically and provides data communication. However, the danger with USB is always that the LapDock's internal hub may do something non-standard and the standard Linux driver on RasPi may not know how to handle it. So before you build any cables, try powering RasPi with its own power supply, and then see if a RasPi USB host port can talk to LapDock over a standard USB A to USB micro-whatever cable.
It should be OK to have RasPi and LapDock both driving the cable with +5V, since there ought to be diodes in there to prevent actual current. Personally, I'd wait until I saw the RasPi schematics (which I suspect they'll publish once the design is verified) and make sure it has a diode to prevent LapDock +5V from affecting RasPi through RasPi's USB host port. In fact, I'd mask off the +5V signal on the cable just to make sure. After all, you don't want to risk damaging either or both devices.
An alternative to the custom cable might be to hack RasPi so the USB host port's +5V goes back to the RasPi's power input. You definitely want to review the RasPi schematic before trying this.
Since this is a SWAG, no warranty is expressed or implied.
SWAG = Scientific Wild-Assed Guess, a term often used by USA consultants.