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