The GPIOPinMuxModeEnum enum defines the possible GPIO Functions. Note that the value here corresponds to the three bit value we would expect to see in the function register for that mode.
public enum GPIOPinMuxModeEnum { GPIOMODE_INPUT = 0x0, GPIOMODE_OUTPUT = 0x1, GPIOMODE_ALT0 = 0x4, GPIOMODE_ALT1 = 0x5, GPIOMODE_ALT2 = 0x6, GPIOMODE_ALT3 = 0x7, GPIOMODE_ALT4 = 0x3, GPIOMODE_ALT5 = 0x2, }