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// 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 0x3f000000//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 <unistd.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <bcm2835.h>
#include <unistd.h>

#define MAXTIMINGS 100

#define DHT11 11
#define DHT22 22
#define AM2302 22

int readDHT(int type, int pin);

int main(int argc, char **argv)
{
if (!bcm2835_init())
return 1;

if (argc != 3) {
printf("usage: %s [11|22|2302] GPIOpin#\n", argv[0]);
printf("example: %s 2302 4 - Read from an AM2302 connected to GPIO #4\n", argv[0]);
return 2;
}
int type = 0;
if (strcmp(argv[1], "11") == 0) type = DHT11;
if (strcmp(argv[1], "22") == 0) type = DHT22;
if (strcmp(argv[1], "2302") == 0) type = AM2302;
if (type == 0) {
printf("Select 11, 22, 2303 as type!\n");
return 3;
}

int dhtpin = atoi(argv[2]);

if (dhtpin <= 0) {
printf("Please select a valid GPIO pin #\n");
return 3;
}


printf("Using pin #%d\n", dhtpin);

readDHT(type, dhtpin);
return 0;

} // main


int bits[250], data[100];
int bitidx = 0;

int readDHT(int type, int pin) {
int counter = 0;
int laststate = HIGH;
int j=0;
int i=0;
// Set GPIO pin to output
bcm2835_gpio_fsel(pin, BCM2835_GPIO_FSEL_OUTP);
bcm2835_gpio_write(pin, HIGH);
usleep(100);
bcm2835_gpio_write(pin, LOW);
usleep(20000);
bcm2835_gpio_fsel(pin, BCM2835_GPIO_FSEL_INPT);

data[0] = data[1] = data[2] = data[3] = data[4] = 0;
// read data!

for (i=0; i< MAXTIMINGS; i++) {
counter = 0;
while ( bcm2835_gpio_lev(pin) == laststate) {
counter++;
nanosleep(1); // overclocking might change this?
if (counter == 100)
break;
}
laststate = bcm2835_gpio_lev(pin);
if (counter == 100) break;
bits[bitidx++] = counter;

if ((i>3) && (i%2 == 0)) {
// shove each bit into the storage bytes
data[j/8] <<= 1;
if (counter > 16)
data[j/8] |= 1;
j++;
}
}


#ifdef DEBUG
for (int i=3; i<bitidx; i+=2) {
printf("bit %d: %d\n", i-3, bits[i]);
printf("bit %d: %d (%d)\n", i-2, bits[i+1], bits[i+1] > 15);
}
#endif

printf("Data (%d): 0x%x 0x%x 0x%x 0x%x 0x%x\n", j, data[0], data[1], data[2], data[3], data[4]);

if ((j >= 39) &&
(data[4] == ((data[0] + data[1] + data[2] + data[3]) & 0xFF)) ) {
// yay!
if (type == DHT11)

printf("Temp = %d *C, Hum = %d \%\n", data[2], data[0]);
if (type == DHT22) {
float f, h;
h = data[0] * 256 + data[1];
printf ("%s\n",h);
h /= 10;

f = (data[2] & 0x7F)* 256 + data[3];
f /= 10.0;
if (data[2] & 0x80) f *= -1;
printf("Temp = %.1f *C, Hum = %.1f \%\n", f, h);
}
return 1;
}

return 0;
}