Raspberry Pi Research

Simple GPIO test

Original gEDA schematic

Modified from RPi Low-level peripherals:
//  How to access GPIO registers from C-code on the Raspberry-Pi
//  Example program
//  15-January-2012
//  Dom and Gert
//  Revised: 15-Feb-2013
// Access from ARM Running Linux
#define BCM2708_PERI_BASE        0x3F000000
#define GPIO_BASE                (BCM2708_PERI_BASE + 0x200000) /* GPIO controller */
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <unistd.h>
#define PAGE_SIZE (4*1024)
#define BLOCK_SIZE (4*1024)
int  mem_fd;
void *gpio_map;
// I/O access
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
void setup_io();
void printButton(int g)
  if (GET_GPIO(g)) // !=0 <-> bit is 1 <- port is HIGH=3.3V
    printf("Button pressed!\n");
  else // port is LOW=0V
    printf("Button released!\n");
int main(int argc, char **argv)
  int g,rep;
  // Set up gpi pointer for direct register access
  // Switch GPIO 7..11 to output mode
  * You are about to change the GPIO settings of your computer.          *
  * Mess this up and it will stop working!                               *
  * It might be a good idea to 'sync' before running this program        *
  * so at least you still have your code changes written to the SD-card! *
  // Set GPIO pins 7-11 to output
  for (g=17; g<=21; g++)
    INP_GPIO(g); // must use INP_GPIO before we can use OUT_GPIO
  for (rep=0; rep<100; rep++)
       GPIO_SET = 1<<g;
	printf ("Setting %d\n", g);
       GPIO_CLR = 1<<g;
	printf ("Clearing %d\n", g);
  return 0;
} // main
// Set up a memory regions to access GPIO
void setup_io()
   /* open /dev/mem */
   if ((mem_fd = open("/dev/mem", O_RDWR|O_SYNC) ) < 0) {
      printf("can't open /dev/mem (sudo?)\n");
   /* mmap GPIO */
   gpio_map = mmap(
      NULL,             //Any adddress in our space will do
      BLOCK_SIZE,       //Map length
      PROT_READ|PROT_WRITE,// Enable reading & writting to mapped memory
      MAP_SHARED,       //Shared with other processes
      mem_fd,           //File to map
      GPIO_BASE         //Offset to GPIO peripheral
   close(mem_fd); //No need to keep mem_fd open after mmap
   if (gpio_map == MAP_FAILED) {
      printf("mmap error %d\n", (int)gpio_map);//errno also set!
   // Always use volatile pointer!
   gpio = (volatile unsigned *)gpio_map;
} // setup_io