Rpi Datasheet 751 GPIO Registers
Revision as of 11:43, 18 February 2012 by Turbo-Frambozenbier (talk | contribs) (Rpi Datasheet 751 GPIO Registers)
Code Example
How to access GPIO registers from C-code on the Raspberry-Pi
// How to access GPIO registers from C-code on the Raspberry-Pi // Example program // 15-January-2012 // Dom and Gert // Access from ARM Running Linux #define BCM2708_PERI_BASE 0x20000000 #define GPIO_BASE (BCM2708_PERI_BASE + 0x200000) /* GPIO controller */ #include <stdio.h> #include <string.h> #include <stdlib.h> #include <dirent.h> #include <fcntl.h> #include <assert.h> #include <sys/mman.h> #include <sys/types.h> #include <sys/stat.h> #include <unistd.h> #define PAGE_SIZE (4*1024) #define BLOCK_SIZE (4*1024) int mem_fd; char *gpio_mem, *gpio_map; char *spi0_mem, *spi0_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 void setup_io(); int main(int argc, char **argv) { int g,rep; // Set up gpi pointer for direct register access setup_io(); // 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=7; g<=11; g++) { INP_GPIO(g); // must use INP_GPIO before we can use OUT_GPIO OUT_GPIO(g); } for (rep=0; rep<10; rep++) { for (g=7; g<=11; g++) { GPIO_SET = 1<<g; sleep(1); } for (g=7; g<=11; g++) { GPIO_CLR = 1<<g; sleep(1); } } 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 \n"); exit (-1); } /* mmap GPIO */ // Allocate MAP block if ((gpio_mem = malloc(BLOCK_SIZE + (PAGE_SIZE-1))) == NULL) { printf("allocation error \n"); exit (-1); } // Make sure pointer is on 4K boundary if ((unsigned long)gpio_mem % PAGE_SIZE) gpio_mem += PAGE_SIZE - ((unsigned long)gpio_mem % PAGE_SIZE); // Now map it gpio_map = (unsigned char *)mmap( (caddr_t)gpio_mem, BLOCK_SIZE, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_FIXED, mem_fd, GPIO_BASE ); if ((long)gpio_map < 0) { printf("mmap error %d\n", (int)gpio_map); exit (-1); } // Always use volatile pointer! gpio = (volatile unsigned *)gpio_map; } // setup_io