picow-iot

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.

Important note about SNI

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.patch

Then, re-build your application making sure it uses your patched changes.

Setup

pico-sdk

You should just need to set up pico-sdk as you would for pico-examples.

cmake

Configure cmake with the following variables, the same as pico-examples.

PICO_SDK_PATH
PICO_BOARD
WIFI_SSID
WIFI_PASSWORD

crypto_consts.h custom header

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.

TODO

Support additional configurations that work with background/FreeRTOS