GP_CLIENTSEL
*reg = GP_CLIENTSEL(pin_num/PINS_PER_COLLECTION);
#define GP_DRIVE0(clct) (GP_CLIENTSEL(clct) + 2)
#define GP_OUTPUT0(clct) (GP_CLIENTSEL(clct) + 3)
#define GP_INPUT(clct) (GP_CLIENTSEL(clct) + 6)