Extreme MQTT on PicoRuby
summary
A C binding called picoruby-net-mqtt-femto runs LWIP's MQTT client on a Raspberry Pi Pico W and implements QoS 0 and QoS 1 with automatic retransmit and exponential backoff. Connection uses cyw43_arch_poll outside the LWIP lock to avoid a deadlock, the receive ring buffer is 4 slots (1,180 bytes), and RAM accounting shows a 150 KB mrbc heap + 90 KB LWIP BSS leaving ~3 KB free so MQTTS fails because Mbed TLS requests ~40 KB; this prototype controls an industrial switch and mostly works within the RP2040 264 KB limit.
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chapters (7)
- 0:00Introduction
- 3:32What is MQTT
- 7:26Implementation layers
- 12:51Source code deep dive
- 17:55Reconnect and sleep
- 20:08Memory limits
- 26:09Wrap-up and limits
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