What is Pinmux?

Different embedded projects deal with different components. Some embedded projects conduct communication with analog sensors. Some projects apply the ON/OFF logic on LEDs/buttons. Some interface with devices on I2C / SPI / UART. These different components have different types of voltage, current, and protocol requirement. We cannot attach an I2C device to a pin that follows the protocol of the SPI bus. Also, we cannot attach an analog sensor to the GPIO pin. This means that we need to have all these types of pins available on the board so that we can do any embedded project. Some embedded projects need interfacing multiple such interfaces. This increases the need of pins available in the CPU. It is not possible to have that many CPU pins. Therefore, there is a need to share the functionalities of available pins. This functionality that shares multiple pins is called Pinmux. Each pin has a set of different modes that support connecting corresponding components. Correct mode for the attached component has to be selected by the user. These pins support multiple voltage and current levels. Voltage and current level of pin can be changed according to the mode selection. BeagleBone SRM lists the possible pin mux modes in the Expansion header pinout tables.

The BeagleBone pins can have maximum eight different modes.

You can see currently configured pin mode using this command:

sudo cat /sys/kernel/debug/pinctrl/44e10800.pinmux/pinmux-pins

You can use utility config-pin to change mode of any pin. Run the following command to get information about this utility:

sudo config-pin