Multiplexing the BBB pins

As accessing hardware resources follows the same process under Android as it does under Linux, it is important to understand how the Linux kernel configures device drivers and allocates them to particular pieces of hardware. It is also necessary to understand how these kernel drivers provide user space interfaces that PacktHAL can interact with.

The BBB's AM3359 processor offers a wide variety of signals on its hundreds of pins. These signals include many different, specialized interface buses and sensor inputs. There are far too many potential signals for the number of pins available to supply these signals to the outside world. To select which signals are available on the pins, the pins are multiplexed, or muxed, to specific signals.

Several of the processor's pins are wired to the connections of the BBB's P8 and P9 headers. The muxing of these particular pins is of great interest to BBB users, as the muxing determines which processor signals and...