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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
// Access from ARM Running Linux
#define BCM2708_PERI_BASE 0x20000000
#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 <errno.h>
#include <string.h>
#define PAGE_SIZE (4*1024)
#define BLOCK_SIZE (4*1024)
#define SER_DAT_PIN 26
#define SER_CLK_PIN 19
#define GATE_PIN 13
#define PAR_CLK_PIN 6
#define SENSE_PIN 5
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 GPIO_ALTER(a) *(gpio+(a==0?10:7)) // alters (a==0: clear, else: set) 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();
void drop_privileges();
void put_on_display(char *content);
void printButton(int g)
{
if (GET_GPIO(g)) // !=0 <-> bit is 1 <- port is HIGH=3.3V
printf("Button pressed!\n");
else // port is LOW=0V
printf("Button released!\n");
}
int main(int argc, char **argv)
{
int rep;
// Set up gpi pointer for direct register access
// setup_io();
// Drop root privileges
drop_privileges();
/************************************************************************\
* 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! *
\************************************************************************/
// must use INP_GPIO before we can use OUT_GPIO
INP_GPIO(SER_DAT_PIN);
OUT_GPIO(SER_DAT_PIN);
INP_GPIO(SER_CLK_PIN);
OUT_GPIO(SER_CLK_PIN);
INP_GPIO(GATE_PIN);
OUT_GPIO(GATE_PIN);
INP_GPIO(PAR_CLK_PIN);
OUT_GPIO(PAR_CLK_PIN);
INP_GPIO(SENSE_PIN);
put_on_display("0123456789abcdefghijklmnopqrstuvwxy");
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) {
perror("can't open /dev/mem");
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) {
perror("mmap error");
exit(-1);
}
// Always use volatile pointer!
gpio = (volatile unsigned *)gpio_map;
} // setup_io
//
// Drop (root) privileges
//
void drop_privileges()
{
/* Drop superuser privileges in correct order */
if (setgid(99) == -1) {
perror("can't drop group privileges");
exit(-1);
}
if (setuid(99) == -1) {
perror("can't drop user privileges");
exit(-1);
}
} // drop_root
//
// Shift the bits provided in content into the display
//
void put_on_display(char *content)
{
char *raw_output;
int line;
raw_output = malloc(7*(5+1));
if (raw_output == NULL) {
perror("malloc failed");
exit(-1);
}
for (line=0; line<7; line++) {
raw_output[line*6] = 1<<line;
memmove(raw_output+1+6*line,content+5*line,5);
}
while (1);
for (line=0; line<7; line++) {
GPIO_CLR = 1<<GATE_PIN; // Licht an
for (int byte=0; byte<6; byte++) {
for (int bit=0; bit<8; bit++) {
GPIO_CLR = 1<<SER_CLK_PIN;
GPIO_ALTER((*(raw_output+6*line+byte)>>bit) & 0x01) = 1<<SER_DAT_PIN;
GPIO_SET = 1<<SER_CLK_PIN;
}
}
usleep(1000);
GPIO_SET = 1<<GATE_PIN; // Licht aus
GPIO_CLR = 1<<PAR_CLK_PIN;
GPIO_SET = 1<<PAR_CLK_PIN;
}
free(raw_output);
} // put_on_screen
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