Page 9 of 21
Chapter 11
Page 203
#include <bcm2835.h>
#include <stdio.h>
#include <sched.h>
#include <sys/mman.h>
uint8_t getByte(int b, int buf[]);
void GetDHT22data(uint8_t pin);
int main(int argc, char **argv)
{
const struct sched_param priority = {1};
sched_setscheduler(0, SCHED_FIFO, &priority);
mlockall(MCL_CURRENT | MCL_FUTURE);
if (!bcm2835_init())
return 1;
bcm2835_gpio_fsel(RPI_BPLUS_GPIO_J8_07, BCM2835_GPIO_FSEL_INPT);
bcm2835_delayMicroseconds(1000);
GetDHT22data(RPI_BPLUS_GPIO_J8_07);
return 0;
}
void GetDHT22data(uint8_t pin)
{
bcm2835_gpio_fsel(pin, BCM2835_GPIO_FSEL_OUTP);
bcm2835_gpio_write(pin, LOW);
bcm2835_delayMicroseconds(1000);
bcm2835_gpio_fsel(pin, BCM2835_GPIO_FSEL_INPT);
int i;
for (i = 1; i < 2000; i++)
{
if (bcm2835_gpio_lev(pin) == 0)
break;
};
uint64_t t;
int buf[41];
int j;
bcm2835_delayMicroseconds(1);
for (j = 0; j < 41; j++)
{
for (i = 1; i < 2000; i++)
{
if (bcm2835_gpio_lev(pin) == 1)
break;
};
t = bcm2835_st_read();
for (i = 1; i < 2000; i++)
{
if (bcm2835_gpio_lev(pin) == 0)
break;
}
buf[j] = (bcm2835_st_read() - t) > 50;
}
int byte1 = getByte(1, buf);
int byte2 = getByte(2, buf);
int byte3 = getByte(3, buf);
int byte4 = getByte(4, buf);
int byte5 = getByte(5, buf);
printf("Checksum %d %d \n\r", byte5, (byte1 + byte2 + byte3 + byte4) & 0xFF);
float humidity = (float)(byte1 << 8 | byte2) / 10.0;
printf("Humidity= %f \n\r", humidity);
float temperature;
int neg = byte3 & 0x80;
byte3 = byte3 & 0x7F;
temperature = (float)(byte3 << 8 | byte4) / 10.0;
if (neg > 0)
temperature = -temperature;
printf("Temperature= %f \n\r", temperature);
return;
}
uint8_t getByte(int b, int buf[])
{
int i;
uint8_t result = 0;
b = (b - 1) * 8 + 1;
for (i = b; i <= b + 7; i++)
{
result = result << 1;
result = result | buf[i];
}
return result;
}
