BCM2835_GPIO_GPFSEL_BITS_PER_PIN
const u_int mask = (1 << BCM2835_GPIO_GPFSEL_BITS_PER_PIN) - 1;
BCM2835_GPIO_GPFSEL_BITS_PER_PIN;
const u_int mask = (1 << BCM2835_GPIO_GPFSEL_BITS_PER_PIN) - 1;
BCM2835_GPIO_GPFSEL_BITS_PER_PIN;