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Simple LoRaWAN example application for mbed OS



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Example LoRaWAN application for Mbed-OS

This is an example application based on Mbed-OS LoRaWAN protocol APIs. The Mbed-OS LoRaWAN stack implementation is compliant with LoRaWAN v1.0.2 specification. See this link for information on support for other LoRaWAN spec versions. This application can work with any Network Server if you have correct credentials for the said Network Server.

Getting Started

Supported Hardware

Mbed Enabled board with an Arduino form factor and one of the following:
- SX126X shield
- SX1276 shield
- SX1272 shield

OR

Mbed Enabled LoRa Module

Import the example application

For Mbed Online Compiler users:
- Select “Import”, then search for “mbed-os-example-lorawan” from “Team mbed-os-examples”. Or simply, import this repo by URL.

  • NOTE: Do NOT select “Update all libraries to latest revision” as this may cause breakage with a new lib version we have not tested.

For mbed-cli users:

$ mbed import mbed-os-example-lorawan
$ cd mbed-os-example-lorawan

#OR

$ git clone git@github.com:ARMmbed/mbed-os-example-lorawan.git
$ cd mbed-os-example-lorawan
$ mbed deploy

Example configuration and radio selection

Because of the pin differences between the SX126x and SX127x radios, example application configuration files are provided with the correct pin sets in the config/ dir of this project.

Please start by selecting the correct example configuration for your radio:
- For Mbed Online Compiler users, this can be done by simply replacing the contents of the mbed_app.json at the root of the project with the content of the correct example configuration in config/ dir.
- For mbed-cli users, the config file can be specifed on the command line with the --app-config option (ie --app-config config/SX12xx_example_config.json)

With the correct config file selected, the user can then provide a pin set for their target board in the NC fields at the top if it is different from the default targets listed. If your device is one of the LoRa modules supported by Mbed-OS, the pin set is already provided for the modules in the target-overrides field of the config file. For more information on supported modules, please refer to the module support section

Add network credentials

Open the file mbed_app.json in the root directory of your application. This file contains all the user specific configurations your application and the Mbed OS LoRaWAN stack need. Network credentials are typically provided by LoRa network provider.

For OTAA

Please add Device EUI, Application EUI and Application Key needed for Over-the-air-activation(OTAA). For example:

"lora.device-eui": "{ YOUR_DEVICE_EUI }",
"lora.application-eui": "{ YOUR_APPLICATION_EUI }",
"lora.application-key": "{ YOUR_APPLICATION_KEY }"

For ABP

For Activation-By-Personalization (ABP) connection method, modify the mbed_app.json to enable ABP. You can do it by simply turning off OTAA. For example:

"lora.over-the-air-activation": false,

In addition to that, you need to provide Application Session Key, Network Session Key and Device Address. For example:

"lora.appskey": "{ YOUR_APPLICATION_SESSION_KEY }",
"lora.nwkskey": "{ YOUR_NETWORK_SESSION_KEY }",
"lora.device-address": " YOUR_DEVICE_ADDRESS_IN_HEX  " 

Configuring the application

The Mbed OS LoRaWAN stack provides a lot of configuration controls to the application through the Mbed OS configuration system. The previous section discusses some of these controls. This section highlights some useful features that you can configure.

Selecting a PHY

The LoRaWAN protocol is subject to various country specific regulations concerning radio emissions. That’s why the Mbed OS LoRaWAN stack provides a LoRaPHY class that you can use to implement any region specific PHY layer. Currently, the Mbed OS LoRaWAN stack provides 10 different country specific implementations of LoRaPHY class. Selection of a specific PHY layer happens at compile time. By default, the Mbed OS LoRaWAN stack uses EU 868 MHz PHY. An example of selecting a PHY can be:

        "phy": {
            "help": "LoRa PHY region. 0 = EU868 (default), 1 = AS923, 2 = AU915, 3 = CN470, 4 = CN779, 5 = EU433, 6 = IN865, 7 = KR920, 8 = US915, 9 = US915_HYBRID",
            "value": "0"
        },

Duty cycling

LoRaWAN v1.0.2 specifcation is exclusively duty cycle based. This application comes with duty cycle enabled by default. In other words, the Mbed OS LoRaWAN stack enforces duty cycle. The stack keeps track of transmissions on the channels in use and schedules transmissions on channels that become available in the shortest time possible. We recommend you keep duty cycle on for compliance with your country specific regulations.

However, you can define a timer value in the application, which you can use to perform a periodic uplink when the duty cycle is turned off. Such a setup should be used only for testing or with a large enough timer value. For example:

"target_overrides": {
    "*": {
        "lora.duty-cycle-on": false
        },
    }
}

Module support

Here is a nonexhaustive list of boards and modules that we have tested with the Mbed OS LoRaWAN stack:

  • MultiTech mDot (SX1272)
  • MultiTech xDot (SX1272)
  • LTEK_FF1705 (SX1272)
  • Advantech Wise 1510 (SX1276)
  • ST B-L072Z-LRWAN1 LoRa┬«Discovery kit with Murata CMWX1ZZABZ-091 module (SX1276)

Here is a list of boards and modules that have been tested by the community:

  • IMST iM880B (SX1272)
  • Embedded Planet Agora (SX1276)

Compiling the application

Use Mbed CLI commands to generate a binary for the application.
For example:

$ mbed compile -m YOUR_TARGET -t ARM

Running the application

Drag and drop the application binary from BUILD/YOUR_TARGET/ARM/mbed-os-example-lora.bin to your Mbed enabled target hardware, which appears as a USB device on your host machine.

Attach a serial console emulator of your choice (for example, PuTTY, Minicom or screen) to your USB device. Set the baudrate to 115200 bit/s, and reset your board by pressing the reset button.

You should see an output similar to this:

Mbed LoRaWANStack initialized 

 CONFIRMED message retries : 3 

 Adaptive data  rate (ADR) - Enabled 

 Connection - In Progress ...

 Connection - Successful 

 Dummy Sensor Value = 2.1 

 25 bytes scheduled for transmission 

 Message Sent to Network Server

[Optional] Adding trace library

To enable Mbed trace, add to your mbed_app.json the following fields:

    "target_overrides": {
        "*": {
            "mbed-trace.enable": true
            }
     }

The trace is disabled by default to save RAM and reduce main stack usage (see chapter Memory optimization).

Please note that some targets with small RAM size (e.g. DISCO_L072CZ_LRWAN1 and MTB_MURATA_ABZ) mbed traces cannot be enabled without increasing the default "main_stack_size": 1024.

[Optional] Memory optimization

Using Arm CC compiler instead of GCC reduces 3K of RAM. Currently the application takes about 15K of static RAM with Arm CC, which spills over for the platforms with 20K of RAM because you need to leave space, about 5K, for dynamic allocation. So if you reduce the application stack size, you can barely fit into the 20K platforms.

For example, add the following into config section in your mbed_app.json:

"main_stack_size": {
    "value": 2048
}

Essentially you can make the whole application with Mbed LoRaWAN stack in 6K if you drop the RTOS from Mbed OS and use a smaller standard C/C++ library like new-lib-nano. Please find instructions here.

For more information, please follow this blog post.

License and contributions

The software is provided under Apache-2.0 license. Contributions to this project are accepted under the same license. Please see contributing.md for more info.

This project contains code from other projects. The original license text is included in those source files. They must comply with our license guide.