Chapter 9. Expansion Boards and Options

We have previously looked at interfacing the custom hardware to the BeagleBone using the GPIO, SPI, and I2C interfaces. While that offers the most flexibility, there are prebuilt, off-the-shelf expansion options for the BeagleBone. These can be a quicker and a simpler way of adding features provided they meet your needs. These options provide a vast library of hardware for the BeagleBone. In this chapter, we will look at the following topics:

• Prebuilt expansion boards

• Example cape offerings

• Configuring Linux for capes

• USB expansion options

• USB versus capes for expansion

• Custom hardware versus off-the-shelf hardware

The BeagleBone capes

Capes are expansion boards that plug in to the expansion connectors, P8 and P9, on the BeagleBone and have a specific pin usage. Capes are defined in the BeagleBone SRM document. Capes are specific to the BeagleBone subfamily and specifically do not include the BeagleBoard Classic or the BeagleBoard xM. Anyone can build a cape using the description in the SRM.

Note

For readers familiar with the microcontroller-based Arduino boards, capes are conceptually similar to a shield for Arduino boards.

As defined in the BeagleBone SRM, capes can be of any shape, but the location of the Ethernet RJ45 connector along with the location of the LED can dictate a specific cut-out pattern. Alternatively, extra tall connectors can be used to clear the Ethernet RJ45 connector. Up to four capes can be stacked using dual-sided connectors. A dual-sided connector is a through hole connector with male pins on one side to fit the expansion connectors P8 and P9, and a female socket on the other...

USB devices on the BeagleBone

The BeagleBone offers a USB host port that allows most USB devices supported by the Linux software to work on the BeagleBone. Many USB devices can be shared with a desktop system or used to exchange data with a desktop system. Consider the following points before using the USB option:

• Power: The BeagleBone can provide up to 500mA on the USB port, but it needs to be powered from the barrel connector for reliable operation. Powering the BeagleBone using the USB option may work but this is outside of the USB specification. Keep in mind the 500mA limit is a USB 2.0 specification, but some mass-marketed USB devices may rely on the 500mA limit to be unenforced.

• Speed: The USB port on the BeagleBone is a USB 2.0 high-speed port and can support high-speed, full-speed, and low-speed devices. However, due to the way the software and hardware is designed, high-speed devices may not archive the same throughput as a desktop system.

• Multimedia: USB multimedia devices such...

Summary

In this chapter, we looked at some of the off-the-shelf options of the BeagleBone expansion. This hardware library comes in two general versions, a USB-based version, and something known as capes. This chapter introduced a lot of off-the-shelf interfacing details.

For capes, the specification is provided in the SRM. The main differentiator for a cape is the identification of EEPROM. This EEPROM identifies hardware resources the cape uses, such as pinmux configuration and electrical requirements. An important detail is that EEPROM does not define software requirements such as drivers. The current software at the time of writing this book uses a cape manager to configure capes. A cape manager associates the cape with a device tree overlay to describe the hardware on the cape to the software. On the BeagleBone Black, new features unique to it appear to the software as a virtual cape.

Another off-the-shelf expansion option is a USB device. USB devices are often mass-marketed devices, which...