MQTT example application for 96Boards Nitrogen

• MQTT example application for 96Boards Nitrogen
  • Overview
    • Requirements
  • Building and flashing
    • Customization
      • Minimal required customization
      • App mode customization
    • Building and flashing with Zephyr SDK
  • Running
    • Configuring and running Linux broker and publisher
    • Flashing and running Zephyr application on the board

Overview

Application acting as MQTT publisher or subscriber (depending on the configuration). It's indented to be used primarily on 96Boards Nitrogen using IPv6 over BLE (6LoWPAN).

Requirements

• Supported boards:
  • 96Boards Nitrogen

Building and flashing

Customization

See config.h, prj.conf and boards/96b_nitrogen.conf files fore some constants and options you might want to customize, like IP addresses, client's ID, etc.

Minimal required customization

User needs to set at least two IPv6 addresses - our own IP and broker's IP in the configuration.
It can be done by modifying boards/96b_nitrogen.conf file or by passing them to west build command as shown below.

• Modifying boards/96b_nitrogen.conf example

CONFIG_NET_CONFIG_MY_IPV6_ADDR="fe80::d9e7:2fff:fe33:959d"
CONFIG_NET_CONFIG_PEER_IPV6_ADDR="fe80::ccc0:79ff:feb3:e40c"

• Passing values in command line example

west build (...) -DCONFIG_NET_CONFIG_MY_IPV6_ADDR="fe80::d9e7:2fff:fe33:959d" \
			   -DCONFIG_NET_CONFIG_PEER_IPV6_ADDR="fe80::ccc0:79ff:feb3:e40c"

App mode customization

In order to change app's behavior from publisher to subscriber set following option anywhere in the configuration files (project or board):

CONFIG_MQTT_SUBSCRIBER=y

or in the west build command line:

west build (...) -DCONFIG_MQTT_SUBSCRIBER=y

Note: by default the application serves as a publisher.

Building and flashing with Zephyr SDK

Provided Zephyr SDK is installed and source on your computer, just do:

$ west build -p auto -b 96b_nitrogen /path/to/this/app -DCONFIG_XYZ  && west flash

from /path/to/zephyrproject/zephyr/ directory.

Note: currently, the earliest code base eligible to run the outbound TCP connection from Zephyr without timeout is v2.6.0-rc1. Please update your sources if needed.

Running

Configuring and running Linux broker and publisher

Use Linux machine as a broker and client for testing. The machine running Linux should be equipped in bluetooth interface as well as MQTT broker/client (for instance Mosquitto).
The example below was tested on 96Boards Avenger running OpenHarmony.

1. Install mosquitto and mosquitto-clients
   If using yocto, please add following line to your conf/local.conf file

IMAGE_INSTALL_append = " mosquitto mosquitto-clients"

mosquitto-clients will install mosquitto_pub and mosquitto_sub apps.

2. Configure mosquitto broker service
   Modify following configuration file in your system:

/etc/mosquitto/mosquitto.conf

by adding

socket_domain ipv6

That will force listener to only use IPv6.
Remember to restart the machine or service after updating the configuration file.

# systemctl restart mosquitto.service

3. Load 6lowpan kernel module

# modprobe bluetooth_6lowpan

Note: 6lowpan module has a bug that prevents it from creating a successful TCP connection. Make sure that this problem is fixed by applying this patch.

4. Enable 6lowpan (should be enabled by default)

# echo 1 > /sys/kernel/debug/bluetooth/6lowpan_enable

5. Initialize LoWPAN connection on Linux

Shortly after board running Zephyr boots, one should be able to see following on the Zephyr's console:

Booting Zephyr OS build zephyr-v2.5.0-3762-gf89771dd9ccf  ***
[00:00:00.269,317] <inf> bt_hci_core: HW Platform: Nordic Semiconductor (0x0002)
[00:00:00.269,348] <inf> bt_hci_core: HW Variant: nRF52x (0x0002)
[00:00:00.269,348] <inf> bt_hci_core: Firmware: Standard Bluetooth controller (0x00) Version 2.6 Build 0
[00:00:00.270,019] <inf> bt_hci_core: Identity: D9:E7:2F:33:95:9D (random)
[00:00:00.270,019] <inf> bt_hci_core: HCI: version 5.2 (0x0b) revision 0x0000, manufacturer 0x05f1
[00:00:00.270,019] <inf> bt_hci_core: LMP: version 5.2 (0x0b) subver 0xffff
[00:00:00.270,477] <inf> net_config: Initializing network
[00:00:00.270,629] <inf> net_config: Waiting interface 1 (0x200011b0) to be up...

at that point, type following in the Linux terminal:

# echo "connect <Nitrogen's MAC address> 2" > /sys/kernel/debug/bluetooth/6lowpan_control

If LoWPAN connection is up, bt0 networking interface should appear.

6. Verbose output from mosquitto
   Normally, mosquitto runs as a daemon in background. To see verbose output from the service perform following:

Disable service first

# systemctl stop mosquitto.service

Run it manually with verbose output

# mosquitto -c /etc/mosquitto/mosquitto.conf -v

7. Publishing something on a topic

In this case we don't want our screen to be flooded by published messages and pings so we keep mosquitto service running silently as is.
Instead we will use shell terminal to publish message to a broker which is also assumed to run locally on our Linux machine.

# -t specifies topic on which we publish
# -m specifies message to be sent in payload
# -d is a debugging option
# Application publishes to localhost by default
mosquitto_pub -t "sensors" -m "test message" -d

Flashing and running Zephyr application on the board

1. Flash the board as described above.
2. Connect to serial port of the boards. Look for the line showing the advertised name and MAC address

[00:00:00.270,019] <inf> bt_hci_core: Identity: D9:E7:2F:33:95:9D (random)

3. Wait until you see

[00:00:00.270,477] <inf> net_config: Initializing network
[00:00:00.270,629] <inf> net_config: Waiting interface 1 (0x200011b0) to be up...

4. Establish LoWPAN connection from the Linux machine

# echo "connect D9:E7:2F:33:95:9D 2" > /sys/kernel/debug/bluetooth/6lowpan_control

The interface in the application should turn up and it will connect to MQTT broker.

[00:00:05.540,588] <inf> net_config: Interface 1 (0x200011b0) coming up
[00:00:05.640,197] <inf> net_config: IPv6 address: fe80::d9e7:2fff:fe33:959d
[00:00:05.640,228] <inf> net_mqtt_publisher_sample: attempting to connect:
[00:00:07.394,958] <inf> net_mqtt_publisher_sample: MQTT client connected!
[00:00:07.394,989] <inf> net_mqtt_publisher_sample: try_to_connect: 0 <OK>
[00:00:07.784,973] <inf> net_mqtt_publisher_sample: SUBACK packet id: 1
[00:00:12.597,595] <inf> net_mqtt_publisher_sample: mqtt_ping: 0 <OK>