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high frequency GPIO17 square wave
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// | |
// How to access GPIO registers from C-code on the Raspberry-Pi | |
// Example program | |
// 15-January-2012 | |
// Dom and Gert | |
// Revised: 15-Feb-2013 | |
// gcc -O6 -I/opt/vc/include -L/opt/vc/lib -lbcm_host blink.c -o blink | |
// Access from ARM Running Linux | |
#define BCM2708_PERI_BASE bcm_host_get_peripheral_address() | |
#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> | |
#include <bcm_host.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(); | |
#define loop(n) { volatile int i; for(i=0; i<n; ++i) {} } | |
int main(int argc, char **argv) | |
{ | |
int N = (argc>1) ? atoi(argv[1]) : 10; | |
setup_io(); INP_GPIO(17); OUT_GPIO(17); // must use INP_GPIO before we can use OUT_GPIO | |
for(;;) { GPIO_SET = 1<<17; loop(N); GPIO_CLR = 1<<17; loop(N); } | |
return 0; | |
} | |
// | |
// 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 */ | |
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; | |
} // setup_io |
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