CoAP Communication#

Get the Metering Data#

The Raspberry Pi gets CoAP metering data from the CoAP meter node using the libcoap client, if you have a node running Wi-SUN SoC CoAP Meter in the same network with the Linux Border Router. Follow the steps below to get CoAP metering data on your Raspberry Pi:

1. Install the libcoap library.

    $sudo apt-get install libcoap2
   
    $sudo apt-get install libcoap2-bin

On more recent linux kernels, use libcoap3 and the commands with the -notls suffix to keep it simple (without TLS authentication), considering that your Wi-SUN network already supports encryption.

1. From the node cli, make sure that you are connected to the network.

   > wisun get wisun.join_state
   
   wisun.connection_state = Operational (5)

2. Get your node global address.

   > wisun get wisun.ip_address_global
   
   wisun.ip_address_global = fd12:3456::be33:acff:fef6:3161

Discover the Available Resources#

The CoAP protocol supports an interoperable discovery feature. A CoAP client can request the attributes hosted by a CoAP server. In the case of the CoAP Meter application, the available resources can be retrieved using the libcoap GET method with the standard discovery entry-point. The following command shows the sensor and LED resources.

$coap-client -m get -N coap://[fd12:3456::be33:acff:fef6:3161]:5683/.well-known/core

</gpio>;ct=40,</sensor>;ct=40,</gpio/led>;rt="led";if="gpio",</sensor/light>;rt="light";if="sensor",</sensor/humidity>;rt="humidity";if="sensor",</sensor/temperature>;rt="temperature";if="sensor",</sensor/all>;rt="all";if="sensor"

Get the CoAP Meter Sensor Data#

On your raspberry Pi, get the CoAP meter sensor data using libcoap with the following command:

$coap-client -m get -N coap://[fd12:3456::be33:acff:fef6:3161]:5683/sensor/all

  {
    "id": 0,
    "temp": 28.18,
    "hum": 46.36,
    "lx": 512
  }

Each sensor data value can be retrieved alone if you specify the corresponding resource in the libcoap command. To retrieve the humidity value, the user can use the following command:

$coap-client -m get -N coap://[fd12:3456::be33:acff:fef6:3161]:5683/sensor/humidity

46.59 %

Note that any machine that has a CoAP client and an IPv6 connectivity with the CoAP Meter node can get the metering data.

Get Help on CoAP Meter Capabilities#

$coap-client -t text -m put -N -B 1 coap://[fd12:3456::be33:acff:fef6:3161]:5683/meter/help

Command example:
coap-client -m get -N -B 10 -t text coap://[$METER_IPV6_ADDR]:5683/$URI_PATH -e "$PAYLOAD"

Requests:
  [PUT/POST/GET] sensor/all:
    - no payload or "async": GET request to get measurement data
    - "register": POST/PUT request to register collector
    - "remove": POST/PUT request to remove collector
  [GET]       sensor/temperature: Request to get temperature
  [GET]       sensor/humidity: Request to get humidity
  [GET]       sensor/light: Request to get light
  [PUT/POST]  gpio/led: Toggle LED0/LED1. Payload is index of the LED: "0" or "1"

Toggle the LEDs#

The libcoap PUT method allows you to toggle the CoAP Meter node LEDs remotely. Use the following command to toggle the LED0.

$coap-client -t text -m put -N -B 1 coap://[fd12:3456::be33:acff:fef6:3161]:5683/gpio/led -e "0"

LED1 can also be toggled with changing the payload to “1”.