Created
November 5, 2017 06:27
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RaspberryPi gpio sample
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#include <stdio.h> | |
#include <stdlib.h> | |
#include <fcntl.h> | |
#include <sys/mman.h> | |
#define PERI_BASE 0x3F000000 | |
#define GPIO_BASE (PERI_BASE + 0x200000) /* GPIO controller */ | |
#define PAGE_SIZE (4*1024) | |
#define BLOCK_SIZE (4*1024) | |
// I/O access | |
volatile unsigned *gpio; | |
static int mem_fd = 0; | |
void check( int condition, char* msg ) | |
{ | |
if( condition ){ printf("%s", msg); exit (-1);} | |
} | |
volatile unsigned * io_mapping(int base_addr) | |
{ | |
char *gpio_mem, *gpio_map; | |
if (!mem_fd) { | |
mem_fd = open("/dev/mem", O_RDWR|O_SYNC); | |
check((mem_fd < 0), "can't open /dev/mem \n"); | |
} | |
gpio_mem = malloc(BLOCK_SIZE + (PAGE_SIZE-1)); | |
check( ( gpio_mem == NULL), "allocation error \n"); | |
// 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 = (char *)mmap((caddr_t)gpio_mem, | |
BLOCK_SIZE, | |
PROT_READ|PROT_WRITE, | |
MAP_SHARED|MAP_FIXED, | |
mem_fd, | |
base_addr ); | |
check( ((long)gpio_map < 0), "mmap error \n"); | |
return (volatile unsigned *)gpio_map; | |
} | |
void main() | |
{ | |
int count; | |
volatile unsigned *addr; | |
gpio = io_mapping(GPIO_BASE); | |
// set GPIO20 to output mode ( bit[2:0] ). offset is 0x8( byte address ) . | |
*( gpio + 0x8/4 ) = (*( gpio + 0x8/4 ) & ~(0x7)) | (0x1 << 0); | |
for( count = 0 ; ; count++){ | |
usleep(1000); | |
addr = ( count % 2 ) ? gpio + 0x1C/4 : gpio + 0x28/4 ; | |
*addr = 0x1 << 20; | |
} | |
} |
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