OTA firmware update using MQTT

This code example demonstrates an over-the-air (OTA) firmware update with the XMC7000 MCU over Ethernet. The device establishes a connection with the designated MQTT broker (this example uses AWS). It periodically checks the job document to see if a new update is available. When a new update is available, it is downloaded and written to the secondary slot (flash). On the next reboot, MCUboot handles image authentication and upgrades.

The upgrade can be either overwrite-based or swap-based. In an overwrite-based upgrade, the new image from the secondary slot is copied to the primary slot after successful validation without the option to revert the upgrade if the new image is inoperable. In a swap-based upgrade, images in the primary and secondary slots are swapped, with the option to revert the upgrade if the new image cannot be validated.

MCUboot is a "secure" bootloader for 32-bit MCUs. For more details, see the README of the mtb-example-mcuboot-basic code example.

The over-the-air update middleware library enables the OTA feature. For more details, see the ota-update middleware repository on GitHub.

The ota-update middleware can function independently and work with any bootloader, as long as the required OTA update handling storage APIs are implemented and registered with OTA agent by the user. This example enables the MCUboot support with the help of ota-bootloader-abstraction middleware. For more details, see README of the ota-bootloader-abstraction middleware.

Build the MCUboot-based bootloader application outside of the OTA MQTT application. It is programmed separately to the device before flashing the OTA MQTT application and is not updated for the life of the device.

View this README on GitHub.

Provide feedback on this code example.

Requirements

ModusToolbox™ v3.2 or later (tested with v3.2)
Board support package (BSP) minimum required version: 4.0.0
Programming language: C
Other tools: Python v3.8.10 or later
Associated parts: XMC7000 MCU

Supported toolchains (make variable 'TOOLCHAIN')

GNU Arm® Embedded Compiler v11.3.1 (GCC_ARM) – Default value of TOOLCHAIN
Arm® Compiler v6.16 (ARM)
IAR C/C++ Compiler v9.40.2 (IAR)

Supported kits (make variable 'TARGET')

XMC7200 Evaluation Kit (KIT_XMC72_EVK) – Default value of TARGET
XMC7200 Evaluation Kit (KIT_XMC72_EVK_MUR_43439M2)

Hardware setup

This example uses the board's default configuration. See the kit user guide to ensure that the board is configured correctly.

Software setup

See the ModusToolbox™ tools package installation guide for information about installing and configuring the tools package.

Install a terminal emulator if you don't have one. Instructions in this document use Tera Term.
This example implements a generic MQTT client that can connect to various MQTT brokers. In this code example, the instructions to set up and run the MQTT client have been provided for the AWS IoT and local Mosquitto MQTT brokers for reference. See section Setting up the MQTT broker for more details.
Install the Python interpreter and add it to the top of the system path in environmental variables. This code example is tested with Python v3.8.10.

Structure and overview

This code example is a dual-core application, where the MCUboot-based bootloader application runs on the CM0+ core and the OTA MQTT application runs on the CM7 core. The OTA MQTT application fetches the new image and places it in the secondary slot (flash), then the MCUboot ensures updating the existing image with the new image. The mtb-example-mcuboot-basic code example is the MCUboot-based bootloader application used for this purpose.

Build and program the MCUboot-based bootloader application and this OTA MQTT application independently. Place them separately in the workspace as you would do for any other two independent applications. For this example, require only the MCUboot-based bootloader application. The root directory of the MCUboot-based bootloader application is referred to as <MCUboot>/<bootloader_app> and the root directory of the OTA MQTT application is referred to as <OTA_MQTT> in this document. An example workspace is as follows:

<example-workspace>
   |
   |-<MCUboot>               # MCUboot-based bootloader and blinky applications directory
   |-<OTA_MQTT>              # OTA MQTT application directory
   |-<mtb_shared>            # Shared library for both the applications
   |

Build and program the MCUboot-based bootloader application into the CM0+ core, and this must be done only once. The OTA MQTT application can then be programmed into the CM7 core and you need to only modify this application for all application purposes.

This README expects you to be familiar with MCUboot and its concepts. See MCUboot basics and MCUboot repository on GitHub for more information.

Using the code example

Create the project

The ModusToolbox™ tools package provides the Project Creator as both a GUI tool and a command line tool.

Use Project Creator GUI

Open the Project Creator GUI tool.

There are several ways to do this, including launching it from the dashboard or from inside the Eclipse IDE. For more details, see the Project Creator user guide (locally available at {ModusToolbox™ install directory}/tools_{version}/project-creator/docs/project-creator.pdf).
On the Choose Board Support Package (BSP) page, select a kit supported by this code example. See Supported kits.

Note: To use this code example for a kit not listed here, you may need to update the source files. If the kit does not have the required resources, the application may not work.
On the Select Application page:

a. Select the Applications(s) Root Path and the Target IDE.

Note: Depending on how you open the Project Creator tool, these fields may be pre-selected for you.

b. Select this code example from the list by enabling its check box.

Note: You can narrow the list of displayed examples by typing in the filter box.

c. (Optional) Change the suggested New Application Name and New BSP Name.

d. Click Create to complete the application creation process.

Use Project Creator CLI

The 'project-creator-cli' tool can be used to create applications from a CLI terminal or from within batch files or shell scripts. This tool is available in the {ModusToolbox™ install directory}/tools_{version}/project-creator/ directory.

Use a CLI terminal to invoke the 'project-creator-cli' tool. On Windows, use the command-line 'modus-shell' program provided in the ModusToolbox™ installation instead of a standard Windows command-line application. This shell provides access to all ModusToolbox™ tools. You can access it by typing "modus-shell" in the search box in the Windows menu. In Linux and macOS, you can use any terminal application.

The following example clones the "mtb-example-ethernet-ota-mqtt" application with the desired name "OTA_MQTT" configured for the KIT_XMC72_EVK BSP into the specified working directory, C:/mtb_projects:

project-creator-cli --board-id KIT_XMC72_EVK --app-id mtb-example-ethernet-ota-mqtt --user-app-name OTA_MQTT --target-dir "C:/mtb_projects"

The 'project-creator-cli' tool has the following arguments:

Argument	Description	Required/optional
`--board-id`	Defined in the field of the BSP manifest	Required
`--app-id`	Defined in the field of the CE manifest	Required
`--target-dir`	Specify the directory in which the application is to be created if you prefer not to use the default current working directory	Optional
`--user-app-name`	Specify the name of the application if you prefer to have a name other than the example's default name	Optional

Note: The project-creator-cli tool uses the git clone and make getlibs commands to fetch the repository and import the required libraries. For details, see the "Project creator tools" section of the ModusToolbox™ tools package user guide (locally available at {ModusToolbox™ install directory}/docs_{version}/mtb_user_guide.pdf).

Open the project

After the project has been created, you can open it in your preferred development environment.

Eclipse IDE

If you opened the Project Creator tool from the included Eclipse IDE, the project will open in Eclipse automatically.

For more details, see the Eclipse IDE for ModusToolbox™ user guide (locally available at {ModusToolbox™ install directory}/docs_{version}/mt_ide_user_guide.pdf).

Visual Studio (VS) Code

Launch VS Code manually, and then open the generated {project-name}.code-workspace file located in the project directory.

For more details, see the Visual Studio Code for ModusToolbox™ user guide (locally available at {ModusToolbox™ install directory}/docs_{version}/mt_vscode_user_guide.pdf).

Keil µVision

Double-click the generated {project-name}.cprj file to launch the Keil µVision IDE.

For more details, see the Keil µVision for ModusToolbox™ user guide (locally available at {ModusToolbox™ install directory}/docs_{version}/mt_uvision_user_guide.pdf).

IAR Embedded Workbench

Open IAR Embedded Workbench manually, and create a new project. Then select the generated {project-name}.ipcf file located in the project directory.

For more details, see the IAR Embedded Workbench for ModusToolbox™ user guide (locally available at {ModusToolbox™ install directory}/docs_{version}/mt_iar_user_guide.pdf).

Command line

If you prefer to use the CLI, open the appropriate terminal, and navigate to the project directory. On Windows, use the command-line 'modus-shell' program; on Linux and macOS, you can use any terminal application. From there, you can run various make commands.

For more details, see the ModusToolbox™ tools package user guide (locally available at {ModusToolbox™ install directory}/docs_{version}/mtb_user_guide.pdf).

Testing flow of OTA MQTT application

To test the flow of an OTA MQTT application, follow the flow chart as shown in Figure 1.

Figure 1. Testing flow of OTA MQTT application

Building and programming MCUboot

The mtb-example-mcuboot-basic code example bundles two applications:

MCUboot-based bootloader application that runs on CM0+ core
Blinky application that runs on CM7 core

Import the mtb-example-mcuboot-basic code example per the instructions in the Using the code example section of its README.

The MCUboot-based bootloader and OTA MQTT applications must have the same understanding of the memory layout. The memory layout is defined through JSON files. The OTA MQTT application provides a set of predefined JSON files that can be readily used.

Note: Both the MCUboot-based bootloader and OTA MQTT applications must use the same JSON file.

The <OTA_MQTT>/flashmap folder contains the pre-defined flashmap JSON files. The following files are supported by this example.

Table 1. Supported JSON files

Target Supported JSON files

KIT_XMC72_EVK
KIT_XMC72_EVK_MUR_43439M2 xmc7200_int_overwrite_single.json
xmc7200_int_swap_single.json
Copy the required flashmap JSON file from the <OTA_HTTPS>/flashmap folder and paste it in the <MCUboot>/flashmap folder.
Modify the value of the FLASH_MAP variable in the <MCUboot>/user_config.mk file to the selected JSON file name from the previous step.
Connect the board to your PC using the provided USB cable through the KitProg3 USB connector.
Open a CLI terminal.

On Linux and macOS, you can use any terminal application. On Windows, from the Start menu, open the modus-shell app.
Navigate the terminal to the <mtb_shared>/mcuboot/<tag>/scripts folder.
Run the following commands to ensure that the required modules are installed.

Note: For Linux and macOS platforms, use python3 instead of python in the following command:
```
python -m pip install -r requirements.txt
```
```
python -m pip install --upgrade cysecuretools==5.0.0
```
Note: cysecuretools is used for signing the image for XMC7000 MCUs.
Open a serial terminal emulator and select the KitProg3 COM port. Set the serial port parameters to 8N1 and 115200 baud.
Build and program the bootloader application per the Step-by-step instructions in its README or follow the instruction as given below.
Using CLI

From the terminal, go to <MCUboot>/bootloader_app and execute the make program_proj command to build and program the MCUboot-based bootloader application using the default toolchain to the selected target.
```
make program_proj
```
After programming, MCUboot starts automatically. Confirm that the UART terminal displays a message as shown in Figure 2:

Figure 2. Booting with no bootable image

Target	Supported JSON files
KIT_XMC72_EVK KIT_XMC72_EVK_MUR_43439M2	xmc7200_int_overwrite_single.json xmc7200_int_swap_single.json

Setting up the MQTT broker

Using AWS IoT Core

Set up the MQTT device (also known as a Thing) in the AWS IoT Core as described in the Getting started with AWS IoT tutorial.

Note: While setting up your device, ensure that the policy associated with this device permits all MQTT operations (iot:Connect, iot:Publish, iot:Receive, and iot:Subscribe) for the resource used by this device. For testing purposes, it is recommended to have the following policy document which allows all MQTT Policy Actions on all Amazon Resource Names (ARNs).
```
{
     "Version": "2012-10-17",
     "Statement": [
         {
             "Effect": "Allow",
             "Action": "iot:*",
             "Resource": "*"
         }
     ]
}
```
Download the following certificates and keys that are created and activated in the previous step:
- A certificate for the AWS IoT Thing - xxxxxxxxxx.aws-client-certificate.crt
- A private key - xxxxxxxxxx.aws-private.key or xxxxxxxxxx.aws-private.pem
- Root CA "RSA 2048 bit key: Amazon Root CA 1" for AWS IoT from CA certificates for server authentication - xxxx.AmazonRootCA1.crt.
Copy the certificates and key, paste it in the <OTA_MQTT>/scripts folder.
Rename the following file names in the <OTA_MQTT>/scripts folder.
- xxxx.AmazonRootCA1.crt to aws_ca.crt
- xxxxxxxxxx.aws-client-certificate.crt to aws_client.crt
- xxxxxxxxxx.aws-private.key to aws_private.key

Mosquitto local broker

This code example uses the locally installable Mosquitto that runs on your computer as the default broker. You can also use one of the other public MQTT brokers listed at https://github.com/mqtt/mqtt.github.io/wiki/public_brokers.

Download the executable from Mosquitto downloads site.
Run the installer to install the software. During installation, uncheck the Service component. Also, note down the installation directory.
Once the installation is complete, add the installation directory to the system PATH environment variable.
Open a CLI terminal.

On Linux and macOS, you can use any terminal application. On Windows, from the Start menu, open the modus-shell app.
Navigate to the <OTA_MQTT>/scripts/ folder.
Execute the following command to generate self-signed SSL certificates and keys. On Linux and macOS, you can get your device local IP address by running the ifconfig command on any terminal application. On Windows, run the ipconfig command on a command prompt.
```
sh generate_ssl_cert.sh <local-ip-address-of-your-pc>
```
Example:
```
sh generate_ssl_cert.sh 192.168.0.10
```
This step will generate the following files in the same <OTA_MQTT>/scripts/ directory:
- mosquitto_ca.crt - Root CA certificate
- mosquitto_ca.key - Root CA private key
- mosquitto_server.crt - Server certificate
- mosquitto_server.key - Server private key
- mosquitto_client.crt - Client certificate
- mosquitto_client.key - Client private key
The <OTA_MQTT>/scripts/mosquitto.conf file is pre-configured for starting the Mosquitto server for this code example. You can edit the file if you wish to make other changes to the broker settings.
Start the MQTT server:

Using the code example in TLS mode (default), execute the following command:
```
mosquitto -v -c mosquitto.conf
```
Using the code example in Non-TLS mode:
1. Edit the <OTA Application>/scripts/mosquitto.conf file.
  1. Change the value of require_certificate parameter to false.
  2. Change the value of listener parameter to 1883.
2. Execute the following command:
```
mosquitto -v -c mosquitto.conf
```

Setting up the MQTT publisher script

Open a CLI terminal.

On Linux and macOS, you can use any terminal application. On Windows, from the Start menu, open modus-shell app.
Navigate to the <OTA_MQTT>/scripts folder.
Run the following command to ensure that the required Python modules are installed.
```
pip install -r requirements.txt
```
Edit the <OTA_MQTT>/scripts/publisher.py file to configure your MQTT publisher (MQTT server).
1. Modify the value of the BOARD variable to your selected TARGET in the following format.
```
if TARGET=APP_KIT_XMC72_EVK, then BOARD = "APP_KIT_XMC72_EVK"

if TARGET=APP_KIT_XMC72_EVK_MUR_43439M2, then BOARD = "APP_KIT_XMC72_EVK_MUR_43439M2"
```
  Example:
```
BOARD = "APP_KIT_XMC72_EVK"
```
2. Modify the value of the AMAZON_BROKER_ADDRESS variable to your custom endpoint on the Settings page of the AWS IoT console. This has the format ABCDEFG1234567.iot.<region>.amazonaws.com.
  
  Note: If you are using the local MQTT broker (e.g., Mosquitto broker), modify the value of MOSQUITTO_BROKER_LOCAL_ADDRESS to the local IP address of your MQTT broker.
3. Ensure the value of the BROKER_ADDRESS variable is AMAZON_BROKER_ADDRESS.
  
  Note: If you are using the local MQTT broker (e.g., Mosquitto broker), modify the value of BROKER_ADDRESS to MOSQUITTO_BROKER_LOCAL_ADDRESS.
4. Ensure that the value of the TLS_ENABLED variable is True.
5. Ensure that the value of the BROKER_PORT variable is 8883.
  
  Note: If you are using the local MQTT broker (e.g., Mosquitto broker), ensure that the value of BROKER_PORT variable is 8884. Currently in the publisher.py file conditional if-else block is used to automatically select a BROKER_PORT value based on the selected MQTT broker.
Ensure that the certificate and key file names in the <OTA_MQTT>/scripts folder and following variables value in the <OTA_MQTT>/scripts/publisher.py file are same.
- ca_certs = "aws_ca.crt"
- certfile = "aws_client.crt"
- keyfile = "aws_private.key"
These variables are present under the AMAZON BROKER section at the last line in the <OTA_MQTT>/scripts/publisher.py file.

Note: If you are using the local MQTT broker (e.g., Mosquitto broker), ensure that the certificate and key file names in the <OTA_MQTT>/scripts folder and these variables value in the <OTA_MQTT>/scripts/publisher.py file under the MOSQUITTO_BROKER_LOCAL_ADDRESS section are the same. Currently in the publisher.py file, the conditional if-else block is used to automatically select the default certificate and key file names based on the selected MQTT broker.
Run the publisher.py Python script.

The scripts take arguments such as the kit name, broker URL, and file path. For details on the supported arguments and their usage, execute the following command:

Note: For Linux and macOS platforms, use python3 instead of python in the following command.
```
python publisher.py --help
```
To start the publisher script for the default settings of this example, execute the following command:
```
python publisher.py tls
```
After starting the publisher, the publisher will connect to the broker and subscribe to the topic as shown in Figure 3.

Figure 3. Publisher connected to the broker and subscribed to the topic

Operation

Connect the board to your PC using the provided USB cable through the KitProg3 USB connector.
Open a terminal program and select the KitProg3 COM port. Set the serial port parameters to 8N1 and 115200 baud.
Modify the PLATFORM variable in the <OTA_MQTT>/Makefile based on the target you have selected. Currently in the Makefile, a conditional if-else block is used to automatically select a value based on the target selected. You can remove it and directly assign a value as per Table 2.

Table 2: Target-specific platform values

Target PLATFORM value

KIT_XMC72_EVK
KIT_XMC72_EVK_MUR_43439M2 XMC7200
Modify the OTA_FLASH_MAP variable in the <OTA_MQTT>/Makefile to change the JSON file name to match the selection made while programming the MCUboot-based bootloader application. Currently in the Makefile, a conditional if-else block is used to automatically select a default flash map file based on the target selected. You can remove it and directly assign the path of the required flash map file to the OTA_FLASH_MAP variable.

The <OTA_MQTT>/flashmap folder contains the predefined flashmap JSON files. The following files are supported by this example:

Table 3: Supported JSON files

Target Supported JSON files

KIT_XMC72_EVK
KIT_XMC72_EVK_MUR_43439M2 xmc7200_int_overwrite_single.json
xmc7200_int_swap_single.json

Note: Both the MCUboot-based bootloader and the OTA MQTT application must use the same JSON file.
Edit the <OTA_MQTT>/configs/ota_app_config.h file to configure your OTA MQTT application:
1. If you are using the local MQTT broker (e.g., Mosquitto broker), make sure that the device running the MQTT local broker and the kit are connected to the same network.
2. Modify the value of the MQTT_BROKER_URL macro to your custom endpoint on the Settings page of the AWS IoT console. This has the format abcdefg1234567.iot.<region>.amazonaws.com.
  
  Note: If you are using the local MQTT broker (e.g., Mosquitto broker), modify the value of MQTT_BROKER_URL to the local IP address of your MQTT broker.
3. Ensure that the value of the MQTT_SERVER_PORT macro is 8883.
  
  Note: If you are using the local MQTT broker (e.g., Mosquitto broker), modify the value of MQTT_SERVER_PORT to 8884. If the code example has been configured to work in non-TLS mode, set the value of MQTT_SERVER_PORT to 1883.
4. By default, this code example works in TLS mode. To use the example in non-TLS mode, modify ENABLE_TLS to false and skip the next step of adding the certificate.
5. Add the certificates and key:
  1. Open a CLI terminal.
    
    On Linux and macOS, you can use any terminal application. On Windows, from the Start menu, open modus-shell app.
  2. Navigate the terminal to <OTA_MQTT>/scripts directory.
  3. Run the format_cert_key.py Python script to generate the string format of the certificate and key files that can be added as a macro. Pass the name of the certificate or key with the extension as an argument to the Python script:
    
    Note: For Linux and macOS platforms, use python3 instead of python in the following command.
```
python format_cert_key.py <one-or-more-file-name-of-certificate-or-key-with-extension>
```
    Example:
```
python format_cert_key.py aws_ca.crt aws_client.crt aws_private.key
```
    You can either convert the values to strings by running the format_cert_key.py scripts like shown above or you can use the HTML utility to convert the certificates and keys from PEM format to C string format. You need to clone the repository from GitHub to use the utility.
  4. Copy the generated strings and add it to the ROOT_CA_CERTIFICATE, CLIENT_CERTIFICATE and CLIENT_KEY macros per the sample shown.
Edit the job document (<OTA_MQTT>/scripts/ota_update.json):
1. Modify the value of Broker to match the value of the MQTT_BROKER_URL and MQTT_BROKER_URL variables present in the <OTA_MQTT>/configs/ota_app_config.h file.
2. Modify the value of the variable Board to your selected TARGET in the following format.
```
if TARGET=APP_KIT_XMC72_EVK, then Board:"APP_KIT_XMC72_EVK"

if TARGET=APP_KIT_XMC72_EVK_MUR_43439M2, then Board:"APP_KIT_XMC72_EVK_MUR_43439M2"
```
  Example:
```
"Board":"APP_KIT_XMC72_EVK",
```
3. Ensure the value of the Port macro is 8883.
  
  Note: If you are using the local MQTT broker (e.g., Mosquitto broker), modify the value of Port to 8884. If the code example has been configured to work in non-TLS mode, set the value of Port to 1883.
Program the board using one of the following:
Using Eclipse IDE
1. Select the application project in the Project Explorer.
2. In the Quick Panel, scroll down, and click <Application Name> Program (KitProg3_MiniProg4).
In other IDEs

Follow the instructions in your preferred IDE.
Using CLI

From the terminal, execute the make program command to build and program the application using the default toolchain to the default target. The default toolchain is specified in the application's Makefile but you can override this value manually:
```
make program TOOLCHAIN=<toolchain>
```
Example:
```
make program TOOLCHAIN=GCC_ARM
```
After programming, MCUboot will validate the primary image. After successfully validating the primary image, MCUboot let the CM7 core run the image from the primary slot. Observe that the user LED blinks at a 1-second interval. Observe the messages on the UART terminal and wait for the device to make the required connections. Once the MQTT client (device) is connected to the broker, it will download the job document (ota_update.json) as shown in Figure 4.

Figure 4. Connection to the MQTT broker and downloaded the job document

Figure 5 shows the logs of publisher while publishing the job document.

Figure 5. Publishing the job document
The job document (ota_update.json) placed in the <OTA_MQTT>/scripts folder has value of Version as 1.0.0. The OTA update will not happen because the OTA MQTT application version and available update version are the same.
Modify the value of the BLINKY_DELAY_MS macro to (100) in the <OTA_MQTT>/source/led_task.c file and change the application version in the <OTA_MQTT>/Makefile by setting APP_VERSION_MINOR to 1.
Build the application (Do not program it to the kit). This new image will be published to the MQTT broker in the following steps to demonstrate the OTA update.
In Eclipse IDE
1. Select the application project in the Project Explorer.
2. In the Quick Panel, scroll down, and click Build <Application Name> Application.
Using CLI
1. From the terminal, execute the make build command to build the application using the default toolchain to the default target. You can specify a toolchain manually:
```
make build TOOLCHAIN=<toolchain>
```
  Example:
```
make build TOOLCHAIN=GCC_ARM
```

Target	`PLATFORM` value
KIT_XMC72_EVK KIT_XMC72_EVK_MUR_43439M2	XMC7200

Target	Supported JSON files
KIT_XMC72_EVK KIT_XMC72_EVK_MUR_43439M2	xmc7200_int_overwrite_single.json xmc7200_int_swap_single.json

After a successful build, edit the <OTA_MQTT>/scripts/ota_update.json file to modify the value of Version to 1.1.0.

The OTA MQTT application now finds and downloads the updated job document resulting in the available update version which is higher than the OTA MQTT application version. So, the OTA MQTT application starts to download the new image as shown in Figure 7 and places it in the secondary slot. Once the download is completed, a soft reset is issued. Then the MCUboot starts the image upgrade process (swapping the images between the primary and secondary slots, after successfully validating the secondary image).

Figure 6 shows the logs of publisher while publishing the new image.

Figure 6. Publishing the new image

Figure 7. Image download
After the image upgrade is completed successfully, MCUboot lets the CM7 core run the new image from the primary slot. Observe that the user LED is now blinking at a 100-millisecond interval and The UART terminal displays the message as shown in Figure 8.

Figure 8. Updated to new image
To test the revert feature of MCUboot, send a bad image as v1.2.0 OTA update. The bad image used in this example is an infinite loop. The watchdog timer will reset the bad image and upon reboot, MCUboot will revert the primary image back to v1.1.0 good image. Edit <OTA_MQTT>/Makefile and add TEST_REVERT to the Defines variable as shown:
```
DEFINES+=TEST_REVERT
```
Note: In an overwrite-based upgrade, the secondary image is simply copied to the primary slot after successful validation. There is no way to revert the upgrade if the secondary image is inoperable. TEST_REVERT feature is not applicable for overwrite-based upgrade.

See the MCUboot basics of the mtb-example-mcuboot-basic code example for more details about the overwrite-based and swap-based upgrades.
Edit the application version in the <OTA_MQTT>/Makefile by setting APP_VERSION_MINOR to 2.
Build the application as per Step 10.
After a successful build, edit the <OTA_MQTT>/scripts/ota_update.json file to modify the value of Version to 1.2.0.
The OTA MQTT application will now find this new v1.2.0 image and update to it. After the update, the watchdog timer resets the devices within a few seconds. Upon reset, MCUboot reverts to the v1.1.0 good image. The UART terminal displays the message as shown in Figure 9.

Figure 9. Reverting to good image

Note: After the last step is complete, the device will be running the v1.1.0 good image and the publisher will still be hosting the v1.2.0 bad image. Because the version of the image hosted by the publisher is greater than the version of the image on the device, the device will redownload the v1.2.0 bad image. This causes an infinite upgrade and reverts the cycle. To avoid this scenario, stop the publisher script after you test the code example. In a production environment, the application is responsible for blacklisting bad image versions and to avoid upgrading to them in the future.

Debugging

You can debug the example to step through the code.

In Eclipse IDE

Use the <Application Name> Debug (KitProg3_MiniProg4) configuration in the Quick Panel. For details, see the "Program and debug" section in the Eclipse IDE for ModusToolbox™ user guide.

In other IDEs

Follow the instructions in your preferred IDE.

Design and implementation

Figure 10 shows the flow of the OTA update process using MQTT. The application which needs OTA updates should run the OTA agent. The OTA agent spawns threads to receive OTA updates when available, without intervening with the application's core functionality.

The initial application resides in the primary slot of the flash. When the OTA agent receives an update, the new image is placed in the secondary slot of the flash. On the next reboot, MCUboot copies the image from the secondary slot into the primary slot, and then CM7 will run the upgraded image from the primary slot.

Figure 10. Overview of OTA update using MQTT

For more details on the features and configurations offered by the ota-update library, see its README.

Both MCUboot-based bootloader and user applications must have an identical understanding of the memory layout. Otherwise, the MCUboot may consider an authentic image as invalid.

For more details on the features and configurations of MCUboot-based bootloader, see the Design and implementation of MCUboot.

This example implements two RTOS tasks: OTA client and LED blinky. Both these tasks are independent and do not communicate with each other. The OTA client task initializes the dependent middleware and starts the OTA agent. The LED task blinks the user LED at a specified delay.

All the source files related to the two tasks are placed under the <OTA_MQTT>/source folder:

Table 4: Source files related to OTA client and LED blinky

File	Description
ota_task.c	Contains the task and functions related to the OTA client
ota_task.h	Contains the public interfaces for the OTA client task
led_task.c	Contains the task and functions related to LED blinking
led_task.h	Contains the public interfaces for the LED blink task
main.c	Initializes the BSP and the retarget-io library, and creates the OTA client and LED blink tasks
heap_usage	Contains the code for printing heap usage

All the scripts and configurations needed for this example are placed under the <OTA_MQTT>/scripts folder:

Table 5: Scripts and configuration files for OTA update over MQTT

File	Description
publisher.py	Python script to communicate with the client and to publish the OTA images
ota_update.json	OTA job document
format_cert_key.py	Python script to convert certificate/key to string format
mosquitto.conf	Pre-configured file for starting the Mosquitto server
generate_ssl_cert.sh	Shell script to generate the required self-signed CA, server, and client certificates

The <OTA_MQTT>/configs folder contains other configurations related to the OTA middleware, FreeRTOS, and MBEDTLS.

Table 6: Application configuration files

File	Description
ota_app_config.h	Contains the OTA configuration macros such as MQTT broker details, certificates, and key
cy_ota_config.h	Contains the OTA middleware level configuration macros
mbedtls_user_config.h	Contains the mbedtls configuration macros
COMPONENT_CM7/FreeRTOSConfig.h	Contains the FreeRTOS configuration macros for XMC7000 family
COMPONENT_MCUBOOT/flash/cy_ota_flash.c	Contains OTA flash operation APIs

Security

The MCUboot-based bootloader application enables the image authentication feature of the MCUboot library. MCUboot verifies the signature of the image in the primary slot every time before booting. In addition, it verifies the signature of the image in the secondary slot before copying it to the primary slot. When these options are enabled, the public key (cypress-test-ec-p256.pub) is embedded within the MCUboot-based bootloader application. The OTA MQTT application is signed using the private key (cypress-test-ec-p256.pem) during the post-build steps, the ota-bootloader-abstraction library handles the image signing for the OTA MQTT application.

The MCUboot-based bootloader application includes a sample public key (cypress-test-ec-p256.pub) under the <MCUboot>/keys directory and the OTA MQTT application includes a sample private key (cypress-test-ec-p256.pem) under the <mtb_shared>/ota-bootloader-abstraction/<tag>/scripts/mcuboot/keys directory. Both the <MCUboot>/keys and <mtb_shared>/ota-bootloader-abstraction/<tag>/scripts/mcuboot/keys directories must have the same pair of keys. Otherwise image (primary/secondary) validation fails; the MCUboot-based bootloader application prints a message "MCUBoot Bootloader found none of bootable images".

Do not use this key pair in your end product. See Generating a key pair for generating a new key pair. Once you generated the key pair, copy the keys to the both <MCUboot>/keys and <mtb_shared>/ota-bootloader-abstraction/<tag>/scripts/mcuboot/keys directories.

Note: See Security to learn more about the image authentication feature of MCUboot.

Resources and settings

Table 7. Application resources

Resource	Alias/object	Purpose
UART (HAL)	cy_retarget_io_uart_obj	UART HAL object used by Retarget-IO for the Debug UART port
GPIO (HAL)	CYBSP_USER_LED	User LED

Related resources

Resources	Links
Application notes	AN234334 – Getting started with XMC7000 MCU on ModusToolbox™ AN234023 – Smart IO usage setup in XMC7000 family
Code examples	Using ModusToolbox™ on GitHub
Device documentation	XMC7000 MCU datasheets XMC7000 reference manuals
Development kits	Select your kits from the Evaluation board finder XMC™ evaluation boards
Libraries on GitHub	mtb-pdl-cat1 – Peripheral Driver Library (PDL) mtb-hal-cat1 – Hardware Abstraction Layer (HAL) library
Middleware on GitHub	libraries – Links to all drivers and middleware MCUboot – Open-source library enabling the development of secure bootloader applications for 32-bit MCUs retarget-io – Utility library to retarget STDIO messages to a UART port ota-update – OTA library and docs wifi-mw-core – Wi-Fi middleware core library and docs ota-bootloader-abstraction - OTA MCUboot-based bootloader abstraction http-client – HTTP client library and docs
Tools	ModusToolbox™ – ModusToolbox™ software is a collection of easy-to-use libraries and tools enabling rapid development with Infineon MCUs for applications ranging from wireless and cloud-connected systems, edge AI/ML, embedded sense and control, to wired USB connectivity using PSoC™ Industrial/IoT MCUs, AIROC™ Wi-Fi and Bluetooth® connectivity devices, XMC™ Industrial MCUs, and EZ-USB™/EZ-PD™ wired connectivity controllers. ModusToolbox™ incorporates a comprehensive set of BSPs, HAL, libraries, configuration tools, and provides support for industry-standard IDEs to fast-track your embedded application development.

Other resources

Infineon provides a wealth of data at www.infineon.com to help you select the right device, and quickly and effectively integrate it into your design.

For XMC™ MCU devices, see 32-bit XMC™ Industrial microcontroller based on Arm® Cortex®-M.

Document history

Document title: CE240102 – OTA firmware update using MQTT

Version	Description of change
1.0.0	New code example

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