bcm.h

/*
 * The peripheral base offset varies between the RPi 2 and 3.
 *  * RPi 2: 0x20000000
 *  * RPi 3: 0x3F000000
 */

#define BCM2708_PERI_BASE 0x3F000000
#define GPIO_BASE         (BCM2708_PERI_BASE + 0x200000) /* GPIO controller */

#define PAGE_SIZE (4*1024)
#define BLOCK_SIZE (4*1024)

// I/O access
static volatile unsigned *gpio;

// GPIO setup macros. Always use INP_GPIO(x) before using OUT_GPIO(x) or SET_GPIO_ALT(x,y)
#define INP_GPIO(g) *(gpio+((g)/10)) &= ~(7<<(((g)%10)*3))
#define OUT_GPIO(g) *(gpio+((g)/10)) |=  (1<<(((g)%10)*3))
#define SET_GPIO_ALT(g,a) *(gpio+(((g)/10))) |= (((a)<=3?(a)+4:(a)==4?3:2)<<(((g)%10)*3))

#define GPIO_SET *(gpio+7)  // sets   bits which are 1 ignores bits which are 0
#define GPIO_CLR *(gpio+10) // clears bits which are 1 ignores bits which are 0

#define GET_GPIO(g) (*(gpio+13)&(1<<g)) // 0 if LOW, (1<<g) if HIGH

#define GPIO_PULL *(gpio+37) // Pull up/pull down
#define GPIO_PULLCLK0 *(gpio+38) // Pull up/pull down clock