This code example demonstrates the implementation of an MQTT Client using the ModusToolbox™ MQTT Client library. The library uses the AWS IoT Device SDK MQTT Client library that includes an MQTT 3.1.1 Client and OPTIGA™ Trust M secure element.

Figure 1. Connection between PSoC™ 6 host MCU and OPTIGA™ Trust M

In this example, the MQTT Client RTOS task reads out a pre-provisioned X.509 certificate out of the secure element and populates the internal MQTT Client configuration to establish a connection with the configured MQTT Broker, and creates the following two tasks:

• Publisher: Publishes messages on a topic when the user button on the kit is pressed.

• Subscriber: Subscribes to the same topic and controls the user LED based on the messages received from the MQTT Broker.

If an unexpected MQTT or Wi-Fi disconnection occurs, the application executes a reconnection mechanism to restore the connection. In addition, all operations related to ECDSA and ECDHE that are performed as part of this demo, i.e., as part of the TLS channel establishment, are automatically accelerated on the secure element.

Figure 2. Connection between an MQTT Client and an MQTT Server

View this README on GitHub.

Provide feedback on this code example.

• ModusToolbox™ software v3.1 or later (tested with v3.1)

• Board support package (BSP) minimum required version: 4.0.0

• Programming language: C

• Associated parts:

  • All PSoC™ 6 MCU parts with SDIO
  • AIROC™ CYW43012 Wi-Fi & Bluetooth™ combo chip
  • AIROC™ CYW4343W Wi-Fi & Bluetooth™ combo chip
  • OPTIGA™ Trust M security solution

Note: Before going through this example you might be also interested in the ModusToolbox™ Training Level 3: WiFi, which explains essential terms for the example, like: TLS, X.509 Certificates, Cloud and MQTT Protocol.

• GNU Arm® embedded compiler v11.3.1 (GCC_ARM) - Default value of TOOLCHAIN
• Arm® compiler v6.16 (ARM)
• IAR C/C++ compiler v9.1 (IAR)

• OPTIGA™ Trust IoT security development kit (CYSBSYSKIT-DEV-01) - Default value of TARGET
• PSoC™ 62S2 evaluation kit (CY8CEVAL-062S2-LAI-43439M2, CY8CEVAL-062S2-LAI-4373M2, CY8CEVAL-062S2-MUR-43439M2, CY8CEVAL-062S2-MUR-4373EM2)
• To use this code example on a different hardware, please follow this guidance

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

Install a terminal emulator if you don't have one. Instructions in this document use Tera Term.

This code example implements a generic MQTT Client that can connect to various MQTT Brokers. In this document, the instructions to set up and run the MQTT Client have been provided for the AWS IoT MQTT Broker for reference.

This example requires no additional software or tools if you are using the MQTT Client with a publicly hosted MQTT Broker.

WARNING: Keep in mind that due to Windows maximum path length limitation, which is defined as 260 characters, the example might fail during build with an "No such file or directory" error due to many submodules added to the project. In such cases, shorten the system path of the project to a minimum; e.g., move it to a different location.

Create the project and open it using one of the following:

project-creator-cli --board-id CYSBSYSKIT-DEV-01 --app-id mtb-example-psoc6-hello-world --user-app-name MyHelloWorld --target-dir "C:/mtb_projects"

• Step 1. Register your X.509 device certificate at AWS IoT
• Step 2. Configure the application
• Step 3. Program
• Alternative methods to verify the publish and subscribe functionality

1. 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. Do not create a client certificate or a corresponding private key because they will be provided by the secure element.

   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": "*"
           }
       ]
   }
   

2. Download the device certificate from the CIRRENT™ Cloud ID as per instructions on the OPTIGA™ Trust IoT Security Development Kit package. On the Device Management tab, select Cloud ID > Actions > Download the list of certificates. A zip archive with a .CSV file inside with the following content is downloaded:

   • Note: If your board doesn't have a QR code to claim the device certificate, you can follow the "Step 3. Program" below and flash your board (even if it doesn't contain the correct configuration). You should be able to see your personal certificate extracted from the OPTIGA™ Trust M secure element which you can use as follows:

   "device_id","group_id","certificate"
   "d6c5a999890f44f843c34a9013e43c0372c59b14","D003",
   "-----BEGIN CERTIFICATE-----
   MIIC3DCCAcSgAwIBAgIU1sWpmYkPRPhDw0qQE+Q8A3LFmxQwDQYJKoZIhvcNAQEL
   BQAwHzELMAkGA1UEBhMCVVMxEDAOBgNVBAoTB2NpcnJlbnQwHhcNMjExMDEzMTkw
   NzE1WhcNMjIxMDEzMTkwNzE1WjAxMRAwDgYDVQQDEwdjaXJyZW50MQswCQYDVQQG
   EwJVUzEQMA4GA1UEChMHY2lycmVudDCCASIwDQYJKoZIhvcNAQEBBQADggEPADCC
   AQoCggEBAPShH3JuN7gs9Px/Gz9Hq4JsiJTS1O47i9QyLIDcMCOEF+HiXh4BsRyE
   7mqev8elqUDA8eKmWr4+CZgOJUmGyegGLCwdtyUyRadDQYvXawAMAF/ICJJdZ9JW
   w9C3yeXiyotRwfozamg4jsJ5gEFItDULmRQeCCamNIYBvIW6cP1X1CtlvABXFhqJ
   oBrtZ5PZrippGFBSI16e4ppcLuVrtW9E9wBcgPSNFv7fNaE9desFV3MNr69euC0a
   r2mSkcnJ9rU+dUMqyu3cyyfVHOTWPR3qGVGo3eLI4yFGJijsXiWaDB1i7F4+c0xn
   LQmy7JJsJP8sZQKXJOrjqK4aYx3h14UCAwEAATANBgkqhkiG9w0BAQsFAAOCAQEA
   dY/5WWFgN4fwHtLQwD3egymiGjd/oTZgFGJ8Ws879fUhsZczdjImOKvb9l3nmFoA
   HXL6QK/iSKaWeNfMJHb0Yvh5wU4yB1elB1yvO3k0r71q276m5Wxq37OHal9nXBfq
   7YdZYLDqzvNpsXmoOIw8UNFbcfD51ICfWCHGx/A8idip6YJjvF9qyYXbK0kzDIpE
   1wEgF2a/A82hBHVt/DSIdSI4tq00i46Ao6DbKelETR4l1I8J/7jjD82Sw82HtoKq
   L+706Bgupj11TRa0uCh8gXBXsmlaK/QQV4QOLo8M+yY6Njj6oUizb513IpkdFs2b
   x0M1J85xUZMOqXOs2nQWLQ==
   -----END CERTIFICATE-----
   "
   

3. Copy and paste the content starting from the -----BEGIN CERTIFICATE----- to -----END CERTIFICATE----- in a PEM file, and name it certificate.pem.

4. Register your certificate.pem file at your AWS IoT endpoint:

   1. In the navigation pane for the AWS IoT console, click Secure, and then click Certificates.

   2. On the Certificates page, click Create a certificate.

   3. Next to Use my certificate, click Get started.

   4. On the Select a CA page, leave the field blank, and then click Next.

      Multi-Account Registration does not require the user to register a certificate authority with AWS.

   5. On the Register existing device certificates page, click Select certificates, and then select the certificate that you recently saved (certificate.pem).

   6. Ensure that the Activate All option is selected, and then click Register certificate.

   7. Click Actions and then click Attach policy to attach the policy that you created. Then click Attach.

   8. Attach your certificate to the Thing you created earlier. On the Certificates page, select the certificate you just created.

   9. Click Actions and then click Attach thing.

   10. On the Attach things to certificate(s) window, select the Thing name and click Attach.

1. Set the Wi-Fi credentials in configs/wifi_config.h to Modify the user configuration files in the configs directory. Modify the macros WIFI_SSID, WIFI_PASSWORD, and WIFI_SECURITY to match with that of the Wi-Fi network that you want to connect to.

2. Navigate to the AWS IoT console. In the navigation pane, choose Settings.

   Your AWS IoT endpoint is displayed in Endpoint. It should look like 1234567890123-ats.iot.us-east-1.amazonaws.com. Make a note of this endpoint.

3. In the configs/mqtt_client_config.h file, set MQTT_BROKER_ADDRESS and MQTT_SNI_HOSTNAME to your custom endpoint on the Settings page of the AWS IoT Console.

4. In the configs/mqtt_client_config.h file, set the following macros:

   • MQTT_PORT: Set to 8883.
   • MQTT_SECURE_CONNECTION: Set to 1.

5. Download the Root CA "ECC 256 bit key (Amazon Root CA 3) for AWS IoT from CA certificates for server authentication.

   Note the following based on the TLS cipher suite:

   • Based on ECDHE_ECDSA: Select the Amazon Root CA 3 (Default).

   • Based on ECDHE_RSA: Select another CA: Amazon Root CA 1.

6. Using these certificates, enter the following parameters in mqtt_client_config.h in PEM format:

   • ROOT_CA_CERTIFICATE - Root CA certificate

     You can either convert the values to strings manually following the format shown in mqtt_client_config.h or you can use the HTML utility available here 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.

     For a full list of configuration macros used in this code example, see Wi-Fi and MQTT configuration macros.

7. (Optional) Modify the configuration macros in the following files according to your application:

   • configs/core_mqtt_config.h used by the MQTT library

   • configs/FreeRTOSConfig.h used by the FreeRTOS library

1. Connect the board to your PC using the provided USB cable through the KitProg3 USB connector.

2. Program the board using one of the following (you don't need any extra configuration for the first part):

   Using Eclipse IDE for ModusToolbox™

   1. Select the application project in the Project Explorer.

   2. In the Quick Panel, scroll down, and click <Application Name> Program (KitProg3_MiniProg4).

   Using CLI

   From the terminal, execute the make program command to build and program the application using the default toolchain to the default target. You can specify a target and toolchain manually:

   make program TARGET=<BSP> TOOLCHAIN=<toolchain>
   

   Example:

   make program TARGET=CYSBSYSKIT-DEV-01 TOOLCHAIN=GCC_ARM
   

3. After programming, the application starts automatically. Observe the messages on the UART terminal, and wait for the device to make all the required connections.

   Figure 3. Application initialization status

   

4. Confirm that the following message is printed on the UART terminal:

   Press the user button (SW2) to publish "TURN ON"/"TURN OFF" on the topic 'ledstatus'...
   

   This message may vary depending on the MQTT topic and publish messages that are configured in the mqtt_client_config.h file.

5. Press the user button (SW2) on the kit to toggle the LED state.

6. Confirm that the user LED state is toggled and the messages received on the subscribed topic are printed on the UART terminal.

   Figure 4. Publisher and subscriber logs

   

This example can be programmed on multiple kits (Only when GENERATE_UNIQUE_CLIENT_ID is set to 1); the user LEDs on all the kits will synchronously toggle with a button press on any kit.

You can individually verify the publish and subscribe functionalities of the MQTT Client if the MQTT Broker supports a Test MQTT Client such as AWS IoT.

• To verify the subscribe functionality: Using the Test MQTT Client, publish messages such as "TURN ON" and "TURN OFF" on the topic specified by the MQTT_PUB_TOPIC macro in mqtt_client_config.h to control the LED state on the kit.

• To verify the publish functionality: From the Test MQTT Client, subscribe to the MQTT topic specified by the MQTT_SUB_TOPIC macro and confirm that the messages published by the kit (when the user button is pressed) are displayed on the Test MQTT Client's console.

You can debug the example to step through the code. In the 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™ software user guide.

Note: (Only while debugging) On the CM4 CPU, some code in main() may execute before the debugger halts at the beginning of main(). This means that some code executes twice – once before the debugger stops execution, and again after the debugger resets the program counter to the beginning of main(). See KBA231071 to learn about this and for the workaround.

This example implements the following RTOS tasks:

• OPTIGA™ Trust
• MQTT Client
• MQTT Publisher
• MQTT Subscriber

The main function initializes the BSP and the retarget-io library, and creates the OPTIGA™ Trust task.

The OPTIGA™ Trust task does the following:

1. Initializes the secure element

2. Extracts the pre-provisioned public key certificate from the chip

3. Populates the public key certificate with the internal configuration for secure communication

4. Initializes the MQTT Client task

The MQTT Client task does the following:

1. Initializes the Wi-Fi Connection Manager (WCM) and connects to a Wi-Fi access point (AP) using the Wi-Fi network credentials that are configured in wifi_config.h

2. Upon a successful Wi-Fi connection, initializes the MQTT library and establishes a connection with the MQTT Broker/Server

The MQTT connection is configured to be secure by default; the secure connection requires a client certificate, a private key, and the Root CA certificate of the MQTT Broker that are configured in mqtt_client_config.h.

After a successful MQTT connection, the Subscriber and Publisher tasks are created. The MQTT Client task then waits for commands from the other two tasks and callbacks to handle events such as unexpected disconnections.

The Subscriber task initializes the user LED GPIO and subscribes to messages on the topic specified by the MQTT_SUB_TOPIC macro that are configured in mqtt_client_config.h. When the Subscriber task receives a message from the Broker, it turns the user LED ON or OFF depending on whether the received message is "TURN ON" or "TURN OFF" (configured using the MQTT_DEVICE_ON_MESSAGE and MQTT_DEVICE_OFF_MESSAGE macros).

The Publisher task sets up the user button GPIO and configures an interrupt for the button. The ISR notifies the Publisher task when a button press is detected. The Publisher task then publishes messages (TURN ON / TURN OFF) on the topic specified by the MQTT_PUB_TOPIC macro. When the publish operation fails, a message is sent over a queue to the MQTT Client task.

An MQTT event callback function mqtt_event_callback() is invoked by the MQTT library for events such as MQTT disconnection and incoming MQTT subscription messages from the MQTT Broker. In the case of an MQTT disconnection, the MQTT Client task is informed about the disconnection using a message queue. When an MQTT subscription message is received, the subscriber callback function implemented in subscriber_task.c is invoked to handle the incoming MQTT message.

The MQTT Client task handles unexpected disconnections in the MQTT or Wi-Fi connections by initiating reconnection to restore the Wi-Fi and MQTT connections. Upon failure, the Publisher and Subscriber tasks are deleted, cleanup operations of various libraries are performed, and then the MQTT client task is terminated.

1. The user button is pressed.

2. The GPIO interrupt service routine (ISR) notifies the Publisher task.

3. The Publisher task publishes a message on a topic.

4. The MQTT Broker sends back the message to the MQTT Client because it is also subscribed to the same topic.

5. When the message is received, the Subscriber task turns the LED ON or OFF. As a result, the user LED toggles every time the user presses the button.

• Configuration
  • I2C Pins
  • Reset and power control pins
  • Initialization in a FreeRTOS task
  • Certificate extraction and MQTT connection configuration
  • mbed TLS configuration
  • Cryptography (ECDSA, ECDHE, Random) functions call routing
  • Custom Certificates and Keys
• Configuring the MQTT Client
  • Wi-Fi and MQTT configuration macros
• Resources and settings

Supported boards have CYBSP_I2C_SCL_OPTIGA and CYBSP_I2C_SDA_OPTIGA defined in their BSP. Alternatively, you can define these in the optiga_lib_mtb_config.h file.

The OPTIGA™ Trust secure element can be controlled via a dedicated reset and a power control line. For example, the power control line is used for entering hibernate mode on the chip.

Do the following:

1. Define OPTIGA_TRUSTM_VDD and OPTIGA_TRUSTM_RST with the corresponding GPIOs in your optiga_lib_config_mtb.h file.

2. Change the reset type (OPTIGA_COMMS_DEFAULT_RESET_TYPE) as appropriate:

   • If both macros are defined: Set this value to 0.

   • If only the reset line is connected: Set this value to 2.

If the Makefile defines PSOC_FREERTOS, it means that the OPTIGA™ Trust library uses a FreeRTOS-based Platform Abstraction Layer (PAL) for the communication. In this case, adhere to the following guidelines:

1. Always initialize the secure element from a task.

2. Allocate enough stack (not more than 3072 bytes) to the OPTIGA™ Trust task, depending on the configuration it needs.

3. Do not start any MQTT-related tasks before the secure element is initialized.

Immediately after the secure element is initialized, you might need to extract the certificate from the chip and assign it to the internal MQTT Client configuration. For an example, see here.

For a successful TLS communication, make sure that only supported handshake methods are selected in your mbed TLS configuration file.

To do this, do one of the following:

• Undefine the following:

  • MBEDTLS_KEY_EXCHANGE_DHE_PSK_ENABLED
  • MBEDTLS_KEY_EXCHANGE_ECDHE_PSK_ENABLED
  • MBEDTLS_KEY_EXCHANGE_RSA_PSK_ENABLED
  • MBEDTLS_KEY_EXCHANGE_RSA_ENABLED
  • MBEDTLS_KEY_EXCHANGE_DHE_RSA_ENABLED
  • MBEDTLS_KEY_EXCHANGE_ECDH_RSA_ENABLED
  • MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED

• Define the following:

  • MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED

If Wi-Fi online provisioning is used, your example will try to establish a connection with several clouds. This restricts the use of many handshake methods. For example, the MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED method might be not available. You can choose the MBEDTLS_KEY_EXCHANGE_ECDHE_RSA_ENABLED and change the Root CA configuration (ROOT_CA_CERTIFICATE) to use the Amazon Root CA 1 (based on RSA 2048), instead of the default value of Amazon Root CA 3 (based on ECC 256).

Ensure that your mbed TLS configuration file has the following macros defined:

• MBEDTLS_ECDH_GEN_PUBLIC_ALT
• MBEDTLS_ECDSA_SIGN_ALT
• MBEDTLS_ECDSA_VERIFY_ALT
• MBEDTLS_ECDH_COMPUTE_SHARED_ALT
• MBEDTLS_ECDSA_GENKEY_ALT

In addition to these macros, ensure that your build includes the $(optiga-trust-m)/examples/mbedtls_port files.

If you don't have your own credentials for the connection, but you would like to generate them, refer to the OPTIGA™ Trust M: Data and certificates management Code Example. If you would like to use existing credentials and would like to change default Object IDs, edit the Makefile and add to the DEFINES the following macros:

• LABEL_DEVICE_PRIVATE_KEY_FOR_TLS='"0xE0F1"' to define a private key slot of the PKCS11 Engine (secure-sockets middleware library), where '"0xE0F1"' value can be of your choice.
• CONFIG_OPTIGA_TRUST_M_PRIVKEY_SLOT=0xE0F1 to define the private key slot of the mbedtls alternative implementation, where 0xe0F1 is the same value as specified above. Keep in mind, that here no additional signs '" are required
• LABEL_DEVICE_CERTIFICATE_FOR_TLS='"0xE0E1"' to define a matching certificate to the private key mentioned above of the PKCS11 Engine, where '"0xE0E1"' value can be of your choice.

Table 1. Application resources

Add MBEDTLS_VERBOSE=4 and ENABLE_SECURE_SOCKETS_LOGS in the Makefile to the end of the DEFINES list after a whitespace to enable an verbose output of mbedtls in case you have a problem during the TLS channel establishment, the Makefile content should be then similar to the following:

DEFINES=$(MBEDTLSFLAGS) $(OPTIGAFLAGS) CYBSP_WIFI_CAPABLE CY_RETARGET_IO_CONVERT_LF_TO_CRLF CY_CRYPTO_HAL_DISABLE MBEDTLS_VERBOSE=4

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 PSoC™ 6 MCU devices, see How to design with PSoC™ 6 MCU – KBA223067 in the Infineon Developer Community.

Document title: CE233736 – OPTIGA™ Trust M: MQTT Client

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