PERIPLEX DHT

This section explains how to interact with the DHT devices generated on Vaaman via Periplex.

How to Generate DHTs on the Vaaman ?

Create the json file:

To generate 5 DHT devices, Your need to create a json file and copy the following content into it.

Tip

how to create the json configuration file for periplex, You can check this Usage Guide

{
    "uart": [],
    "i2cmaster": [],
    "gpio": [],
    "pwm": [],
    "ws": [],
    "spi": [],
    "onewire": [],
    "can": [],
    "i2s": [],
    "i2cslave": [],
    "jtag": [],
    "dht": [
       {
          "id": 0,
          "DHT": "GPIOT_RXP28"
       },
       {
          "id": 1,
          "DHT": "GPIOL_73"
       },
       {
          "id": 2,
          "DHT": "GPIOR_173"
       },
       {
          "id": 3,
          "DHT": "GPIOR_174"
       },
       {
          "id": 4,
          "DHT": "GPIOT_RXN27"
       }
    ]
}

Run the periplex-sync command:
- For example, if the JSON configuration for 5 DHT is stored into the device.json file, the periplex-sync command would look like this:
```
sudo periplex-sync -p device.json
```
- After successfully running of periplex-sync command, it will ask for the reboot.

Reboot the board:

After rebooting, all configurations have been successfully applied.
You will get the 5 DHT devices generated through periplex like this:

  autofs           gpiochip2    loop5         periplex   tty13  tty35  tty57     usbmon6      vcsu3
  block            gpiochip3    loop6         port       tty14  tty36  tty58     v4l          vcsu4
  btrfs-control    gpiochip4    loop7         ptmx       tty15  tty37  tty59     v4l-subdev0  vcsu5
  bus              gpiochip5    loop-control  pts        tty16  tty38  tty6      v4l-subdev1  vcsu6
  cec0             hdmi_hdcp1x  mali0         ram0       tty17  tty39  tty60     v4l-subdev2  vcsu7
  char             hugepages    mapper        random     tty18  tty4   tty61     vcs          vendor_storage
  console          hwrng        media0        rfkill     tty19  tty40  tty62     vcs1         vhci
  cpu_dma_latency  i2c-0        mem           rga        tty2   tty41  tty63     vcs2         video0
  crypto           i2c-1        mmcblk0       rk_cec     tty20  tty42  tty7      vcs3         video1
  dht-0            i2c-10       mmcblk0boot0  rtc        tty21  tty43  tty8      vcs4         video2
  dht-1            i2c-4        mmcblk0boot1  rtc0       tty22  tty44  tty9      vcs5         video3
  dht-2            i2c-7        mmcblk0p1     shm        tty23  tty45  ttyFIQ0   vcs6         video4
  dht-3            i2c-9        mmcblk0p2     snd        tty24  tty46  ttyS0     vcs7         video-dec0
  dht-4            iep          mmcblk0p3     spidev0.0  tty25  tty47  ubi_ctrl  vcsa         video-enc0
  disk             iio:device0  mmcblk0p4     stderr     tty26  tty48  uhid      vcsa1        watchdog
  dma_heap         initctl      mmcblk0p5     stdin      tty27  tty49  uinput    vcsa2        watchdog0
  dri              input        mmcblk0p6     stdout     tty28  tty5   urandom   vcsa3        zero
  drm_dp_aux0      kmsg         mmcblk0p7     sw_sync    tty29  tty50  usb-ffs   vcsa4        zram0
  fb0              log          mmcblk0p8     tty        tty3   tty51  usbmon0   vcsa5
  fd               loop0        mmcblk0rpmb   tty0       tty30  tty52  usbmon1   vcsa6
  full             loop1        mpp_service   tty1       tty31  tty53  usbmon2   vcsa7
  fuse             loop2        mqueue        tty10      tty32  tty54  usbmon3   vcsu
  gpiochip0        loop3        net           tty11      tty33  tty55  usbmon4   vcsu1
  gpiochip1        loop4        null          tty12      tty34  tty56  usbmon5   vcsu2

How to interact with the generated DHTs ?

The periplex platform dynamically generates DHT devices, which are accessible through device nodes such as:

/dev/dht-0
/dev/dht-1
/dev/dht-2
...

These DHT device nodes allow seamless access to temperature and humidity data from connected DHT sensors such as DHT11, DHT21, and DHT22.

Example of using DHT device node

You can read data from the DHT sensor using standard file operations. For example, you can use this script to read temperature and humidity data:

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>

#include <sys/ioctl.h>

#define SET_DHT_SENSOR_TYPE _IOWR('a', 'b', enum dht_type *)
#define MEASURE_DHT_VALUE _IOWR('a', 'c', void *)
#define GET_TEMP_HUMD _IOWR('a', 'd', char *)

enum dht_type {
    DHT11 = 0,
    DHT21 = 1,
    DHT22 = 2
};

struct buf {
    int humidity;
    int temperature;
};

int main(int argc, char *argv[]) {
    if (argc <= 1) {
        printf("Usage: %s <devpath>\n", argv[0]);
        return 1;
    }

    const char *filepath = argv[1];

    int fd = open(filepath, O_RDWR);
    if (fd < 0) {
        printf("%s no such file found\n", filepath);
        return 1;
    }

    enum dht_type type = DHT11;

    int ret = ioctl(fd, SET_DHT_SENSOR_TYPE, &type);
    if (ret < 0) {
        printf("sensor type set failed\n");
        close(fd);
        return 1;
    }

    ret = ioctl(fd, MEASURE_DHT_VALUE, NULL);
    if (ret < 0) {
        printf("measure failed\n");
        close(fd);
        return 1;
    }

    struct buf b;

    ret = ioctl(fd, GET_TEMP_HUMD, &b);
    if (ret < 0) {
        printf("temp get failed\n");
        close(fd);
        return 1;
    }

    printf("Humidity: %d Temperature: %f C\n", b.humidity / 10,
            (float) b.temperature / 10);

    close(fd);
    return ret;
}

you can use gcc to compile the above code and run the executable with the DHT device node as an argument like this:

vicharak@vicharak:~$gcc dht_read.c -o dht_read
vicharak@vicharak:~$sudo ./dht_read /dev/dht-0

you will get the temperature and humidity data from the connected DHT sensor like this:

Humidity: 37 Temperature: 28.500000 C

Note

Make sure to run the executable with sudo to have the necessary permissions to access the device nodes.
Ensure that the DHT sensor is properly connected to the specified GPIO pin corresponding to the DHT device node being accessed.

PERIPLEX JTAG

Frequently Asked Questions