In this chapter, we introduced you to the SPI bus. You constructed a circuit that connected an SPI pressure and temperature sensor breakout board to the BBB, and you learned about the portions of the PacktHAL init.{ro.hardware}.rc file's Device Tree overlay that are responsible for configuring and making the SPI bus and spidev device driver available for your app's use. The sensor app in this chapter demonstrated how complex tasks in the HAL can be hidden from the app using a small set of functions that hide the low-level details. These simplified PacktHAL function calls can be made from a class derived from AsyncTask to perform more complex interfacing tasks simply from within an app.

In the next chapter, you will learn about combining GPIO, I2C, and SPI together into an app capable of providing a complete hardware solution that uses a long-lived hardware-interfacing thread.