Introduction

Hello and Welcome to Part 1 of Patient Monitoring System using 96Boards blog series. As specified in the Introductory blog, this blog will cover the BLE mesh implementation using zephyr running on 96Boards IE.

BLE Mesh using zephyr

BLE Mesh functionality in zephyr is implemented by Johan Hedberg of Intel. Still, the implementation is in early stage but so far most of the essential features have been supported. One of the advantages of using BLE mesh in zephyr instead of any third-party SDK is the code organization. The zephyr code structure makes it easy for the developers to poke into the source code to see what’s going on and how the stack is working. And to our own benefits, they have included some sample applications and tests for making the lives of Application developers easier :-)

Below are some of the resources which will help getting started on BLE mesh using zephyr:

https://github.com/zephyrproject-rtos/zephyr/tree/master/samples/bluetooth/mesh
https://github.com/zephyrproject-rtos/zephyr/tree/master/samples/bluetooth/mesh_demo
https://github.com/zephyrproject-rtos/zephyr/tree/master/samples/boards/nrf52/mesh/onoff-app
https://github.com/zephyrproject-rtos/zephyr/tree/master/tests/bluetooth/mesh
https://github.com/zephyrproject-rtos/zephyr/tree/master/tests/bluetooth/mesh_shell
https://www.zephyrproject.org/announcing-bluetooth-mesh-support-in-zephyr-project/

Before we jump into the implementation of BLE mesh using zephyr on 96Boards IE, we will skim through the basic concepts of BLE mesh.

Mesh network is a common terminology in the networking world. It involves the way of inter-connecting devices (a.k.a nodes) in a network with each other directly and indirectly. The non-hierarchial way of connecting devices to each other makes this mesh network special among other networking topologies. Bluetooth ® wireless technology uses this topology to connect nodes within a network so that it can extend its coverage and efficiently communicate with each node in a network.

BLE mesh network consists of nodes (BLE compatible devices) which takes part in the network and each node consists of Elements, uniquely addressable entities in a network. Each node has to be provisioned by a provisioner (Mobile/Laptop in most case) in order to take part in the mesh network. Provisioning involves assigning the Node address to mesh nodes, exchanging public/private keys, and so on. Once the mode has been provisioned, it is a part of the mesh network.

Next step after provisioning is configuring the node. Again this needs to be done by the provisioner. Each element in a node will have Models, which defines the behaviors of each node. There are Standard and Vendor specific models. In our project, we are going to use only Standard models defined by Bluetooth specification. Configuring involves assigning the AppKey and binding it to the models. We can also add Subscription/Publishing information for each element in a network.

Once a node has been provisioned and configured, it can start sending/receiving messages within the network.

In this blog, we will use two nodes to form a BLE Mesh network. One will act as a server and other will act as a client node. The role of client node here is to send ‘Sensor Get’ request to the server for sending the Sensor Status messages. If the server receives ‘Sensor Get’ request from the client, it will send the ‘Sensor Status’ message in response. Then the client can use this response to find out the sensor readings.

Setting up the Sensor Nodes

For the sake of this blog, I am going to use 96Boards Carbon for the nodes. But you can use either 96Boards Carbon/Nitrogen to follow this blog. Both are well supported in zephyr.

96Boards Carbon has a BLE Co-Processor for providing Bluetooth capabilities to the board. This project can run either on the main STM32 chip or directly on the BLE co-processor. But it is recommended to use the STM32 microcontroller for implementing this project since there is no debug port exposed on the board for the network co-processor. It will make it hard to see the debug outputs without using any external utilities.

In the case of using STM32 chip, hci_spi example application needs to be programmed on the co-processor for providing the HCI interface, thus giving Bluetooth functionality to the STM32.

Programming nRF Co-Processor

Follow the below steps to flash the hci_spi sample application to the nRF co-processor on 96Boards Carbon using a Linux enabled host machine.

First setup the development environment as mentioned here.

$ git clone https://github.com/Mani-Sadhasivam/zephyr.git
$ cd zephyr
$ git checkout ble_mesh
$ source zephyr-env.sh
$ samples/bluetooth/hci_spi
$ mkdir build
$ cd build
$ cmake -DBOARD=96b_carbon_nrf51 ..
$ make

Once the application is successfully built, flash the binary onto the nRF chip by following this guide. Now, this chip can provide HCI interface to STM32 via SPI.

Note: You need to execute this section for all Carbon boards to be used as nodes. As per this blog, execute it on 2 Carbon boards.

Programming Sensor Server application

Next step is to program the Sensor Server application to the STM32 chip on one of the Carbon board to act as a Sensor Server.

Move to the top of the cloned zephyr repository.

$ cd zephyr
$ cd samples/bluetooth/ble_mesh_srv
$ mkdir build
$ cd build
$ cmake -DBOARD=96b_carbon ..
$ make

Now, the built binary can be flashed by following this guide. Once the application binary is flashed, connect the UART port of Carbon board to the Host machine using USB-A to USB-B Micro cable and bring up the serial emulation tool like minicom on the corresponding port.

After board reset you should see the below message on the serial port:

Initializing...
Bluetooth initialized
Mesh initialized

Programming Sensor Client application

As like the Sensor Server application, Sensor Client application is also need to be programmed on another Carbon board.

Move to the top of the cloned zephyr repository.

$ cd zephyr
$ cd samples/bluetooth/ble_mesh_cli
$ mkdir build
$ cd build
$ cmake -DBOARD=96b_carbon ..
$ make

After board reset you should see the below message on the serial port:

Initializing...
Bluetooth initialized
Mesh initialized

Provisioning and Configuring the Nodes

The final step is to provision and configure both the nodes. This requires the meshctl utility in Bluez stack. Install Bluez by following the below steps.

$ git clone https://git.kernel.org/pub/scm/bluetooth/bluez.git
$ cd bluez
$ bootstrap
$ ./configure --prefix=/usr --mandir=/usr/share/man --sysconfdir=/etc --localstatedir=/var --enable-mesh
$ make
$ sudo make install

Above commands will install Bluez on the host machine with BLE mesh support.

Server Node

Now, execute the below steps for provisioning and configuring the Server node:

$ cd bluez/mesh
$ meshctl

This will bring up the meshctl command prompt.

[meshctl]# discover-unprovisioned on
[meshctl]# provision dddd

Here we are provisioning the node dddd which is default address for all un-provisioned nodes.

Now, enter the OOB number displayed in the Server’s serial terminal here.

[meshctl]# menu config
[meshctl]# target 0100

Here 0100 is the node name after provision. Modify it based on the assigned address.

Now, generate AppKey and bind it to the 0th element of Sensor Server model (1100).

[meshctl]# appkey-add 1
[meshctl]# bind 0 1 1100

Next, add the subscription and publish info to the models.

[meshctl]# sub-add 0100 c000 1100
[meshctl]# pub-set 0100 c000 1 0 0 1100

Once, all the above commands are executed successfully, we can assume that the Sensor node is configured.

Client Node

Now, execute the below steps for provisioning and configuring the Client node:

$ cd bluez/mesh
$ meshctl
[meshctl]# discover-unprovisioned on
[meshctl]# provision dddd

Now, enter the OOB number displayed in the Client’s serial terminal here.

[meshctl]# menu config
[meshctl]# target 0101

Here 0101 is the node name after provision. Modify it based on the assigned address.

Now, generate AppKey and bind it to the 0th element of Client Sensor model (1102).

[meshctl]# appkey-add 1
[meshctl]# bind 0 1 1102

Next, add the subscription and publish info to the models.

[meshctl]# sub-add 0101 c000 1102
[meshctl]# pub-set 0101 c000 1 0 0 1102

Once, all the above commands are executed successfully, we can assume that the Client node is configured.

Mesh implementation

Finally, after completing the above-mentioned steps, you can see the following output in Server and Client serial terminals.

Server

Sensor Status Get request received
Sensor status sent with OpCode 0x00000052

Client

Sensor status Get request sent with OpCode 0x00008231
Got the sensor status
Sensor ID: 0x2a1f
Sensor value: 0x001b

Below is the behavior of the mesh network:

Client node sends the Sensor Get request to the address group C000 set during configuration.
Server node receives the message since it is subscribed to the group address C000
Server node sends the Sensor Status as a response to the Sensor Get message
Client node receives the message from the server, it parses and prints the value in the terminal.

Note: Here the temperature data is hardcoded as 27.

This demonstrates the BLE mesh network with two nodes acting as a Server and Client. Here the temperature data is sent from Server to Client every time when the Client raises the request.

Pain Points

Even though we got the mesh network setup, there is still no way to store the provisioning and configuring information on the non-volatile memory like flash. This will make us do the provision and configure every time after node restart. This feature is being worked on and I hope that it will be available soon.

Conclusion

So that’s it for the Part 1 of Patient Monitoring System using 96Boards blog series. I hope this blog demonstrated the BLE mesh functionality with two nodes acting as a Server and Client and exchanging data between them. This isn’t a full-fledged mesh implementation but rather a getting started the demo.

In the next blog post, we will see how to exchange the real sensor data between mesh nodes and a Gateway.