Utility to switch Raspberry-Pi GPIO pin functions by Tim Giles 01/04/2013

pi-gpio-switch

        /*
        Utility to switch Raspberry-Pi GPIO pin functions
        Tim Giles 01/04/2013
     
        Usage:
        $ gpio_alt -p PIN_NUMBER -f ALT_NUMBER
     
        Based on RPi code from Dom and Gert, 15-Feb-2013, <http://elinux.org/RPi_Low-level_peripherals#C_2>
        and Gnu getopt() example <http://www.gnu.org/software/libc/manual/html_node/Example-of-Getopt.html#Example-of-Getopt>
        */
     
        #include <ctype.h>
        #include <stdio.h>
        #include <stdlib.h>
        #include <unistd.h>
        #include <fcntl.h>
        #include <sys/mman.h>
     
        #define BCM2708_PERI_BASE        0x20000000
        #define GPIO_BASE                (BCM2708_PERI_BASE + 0x200000) /* GPIO controller */
        #define PAGE_SIZE (4*1024)
        #define BLOCK_SIZE (4*1024)
     
        int  mem_fd;
        void *gpio_map;
        volatile unsigned *gpio;
        void setup_io();
     
        // 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
     
     
     
        int main (int argc, char **argv) {
          int opt, flag, n_pin, n_alt;
          flag=0;
     
          while ((opt = getopt (argc, argv, "hp:f:")) != -1) {
            switch (opt) {
            case 'h':
              break;
            case 'p':
              n_pin = atoi(optarg); flag |= 0b0001; break;
            case 'f':
              n_alt = atoi(optarg); flag |= 0b0010; break;
            case '?':
              // getopt() prints error messages, so don't need to repeat them here
              return 1;
            default:
              abort ();
            }
          }
         
          if (flag != 0b0011) {
            fprintf (stderr, "Usage:\n$ gpio_alt -p PIN_NUM -f FUNC_NUM\n");
            return 1;
          }
         
          setup_io(); // Set up gpi pointer for direct register access
          INP_GPIO(n_pin);  // Always use INP_GPIO(x) before using SET_GPIO_ALT(x,y)
          SET_GPIO_ALT(n_pin, n_alt);
         
          printf("Set pin %i to alternative-function %i\n", n_pin, n_alt);
         
          return 0;
        }
     
     
     
        void setup_io() {
           /* open /dev/mem */
           if ((mem_fd = open("/dev/mem", O_RDWR|O_SYNC) ) < 0) {
              printf("can't open /dev/mem \n");
              exit(-1);
           }
     
           /* 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!
              exit(-1);
           }
     
           // Always use volatile pointer!
           gpio = (volatile unsigned *)gpio_map;
        }