In this chapter, we explained how Android uses a HAL to allow Android managers to provide hardware access to apps. We introduced you to PacktHAL that can be used to interface with all of the examples throughout this book. You configured your BBBAndroid image to use PacktHAL, and you modified your NDK installation to build PacktHAL into your apps.

We also showed which pins of the BBB's P8/P9 headers can be multiplexed, what the Device Tree is and how it is used to multiplex pins, and how the capemgr loads Device Tree overlays to dynamically mux the BBB's pins.

In the next chapter, you'll put PacktHAL to work and build your first hardware-interfacing app using GPIOs.