This is a small example project that demonstrates connecting to an MQTT broker with a Pico W. It uses lwIP's MQTT client and mbedtls to connect to a broker and transmit a message to a topic.
Some cloud providers (e.g. AWS) require that SNI be enabled on the client. There does not appear to be a way to configure lwip's MQTT app client to set up SNI. This code uses a patched version of mqtt.c to support SNI.
If you want to connect to a cloud provider that requires SNI you'll need to apply the patch to the copy of LWIP thats used by the Pico SDK.
To do so, in your expansion of pico-sdk, run
cd lib/lwip
git apply path/to/mqtt-sni.patchThen, re-build your application making sure it uses your patched changes.
You should just need to set up pico-sdk as you would for pico-examples.
Configure cmake with the following variables, the same as pico-examples.
- PICO_SDK_PATH
- PICO_BOARD
- WIFI_SSID
- WIFI_PASSWORD
The build relies on a simple header file (crypto_consts.h) to provide cryptographic keys and certificates as well.
See crytpo_consts_example.h for a setup for AWS IoT and Mosquitto test servers.
- Support additional configurations that work with background/FreeRTOS