The M3 can configure any pin that has been assigned to the Master subsystem MUX. First, the M3 selects whether the pin should be a GPIO or a peripheral. The GPIO selection is the default pin, when configured it will be routed to the M3 data and direction registers, as well as the interrupt control logic that feeds the nested vectored interrupt controller. If the pin is configured as a peripheral function, then the M3 will select which of the available peripherals will be connected. Only the peripherals on the Master subsystem are available to the M3 MUX. There is no Control subsystem peripherals available. For flexibility as well as compatibility, two MUX mapping schemes are available. The primary pin mapping, which is the default, provides maximum compatibility for Stellaris devices. To gain additional pin mapping flexibility, the application can select an alternate mapping using the GPIO A Select register. This alternate mapping is similar to the C2000 devices. Note the pin can also be enabled or disabled, which is not shown here, if it is enabled but assigned to the C28x MUX, then the M3 can still read the state of the pin.