Peripheral and subsystem assignment

System GPIO pins can be allocated to peripherals with dedicated pins or subsystems such as trace and debug.

The pins of the system are listed in Pin assignments.

By default, all pins are assigned to GPIO or peripherals with PSEL registers. This is the default value of the CTRLSEL value in register PIN_CNF[n] (n=0..31) (Retained).

To allocate a pin to a peripheral or subsystem with dedicated pins, such as GRTC or TND, change the CTRLSEL value in register PIN_CNF[n] (n=0..31) (Retained) for that pin. This will connect the pin to the subsystem or peripheral.

Only the peripheral or subsystem where the pin was allocated can observe and control that pin's state. Reading a pin that is not allocated to the current subsystem will return zero, and writes will be ignored. If a pin is allocated to a subsystem that cannot access it, the pin stays under control of the GPIO peripheral.

When CTRLSEL is used to allocate a peripheral or subsystem, reading the GPIO peripheral registers will not reveal the state of the pins.

The following figure illustrates how to assign a pin to a peripheral that has dedicated pins, or a subsystem such as trace and debug.

For details on pin security, see Security.