Capemgr keeps track of the BeagleBone Black's expansion boards, known as capes

The Texas Instruments Sitara AM3359 [1] processor of the BeagleBone Black (BBB) provides a large number of I/O signals that implement GPIO and various communication interfaces (SPI, I2C, UARTs). Inside the processor, these signals are routed to the chip's physical pins, and those pins are wired to the pins of the BBB's P8 and P9 expansion connectors, providing direct access to the processor's I/O signals for all sorts of different interfacing projects. Whereas the Raspberry Pi makes 26 pins available via its P1 expansion connector, the BBB makes a whopping 92 pins available via its P8 and P9 connectors. This gives the BBB a great deal of flexibility as an interfacing platform. The locations of the P8 and P9 connectors on the BBB can be seen in Figure 1.

Far more signals are available internally within the BBB's processor than there are pins on the chip, so not all of these signals can be made available to the outside world at the same time. Users must choose which signal to multiplex (mux), or map, to each processor pin to make the most efficient use of the platform's resources for a particular application. Understanding what each signal does and how it works is necessary to mux the pins effectively and utilize the BBB platform to its full potential.

Capes

Both the BBB and its predecessor, the BeagleBone, support a variety of expansion boards known as "cape" boards or "capes." Capes interface with the BeagleBone family of boards via P8 and P9 to provide additional hardware functionality. Each cape expects the processor's I/O signals to be muxed to a particular configuration so that the cape can interface properly with the processor. Some capes provide pass-through connectors so that up to four capes can be connected to the BBB simultaneously by stacking capes one on top of another. For more information on exactly what a cape is, see the box "What Makes Your Hardware a Cape?"

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