I understand that you are able to send vectors up to [1x20] from Simulink to Node-RED via MQTT using STM32, but longer vectors like [1x21] are not showing up. This likely happens due to limitations in the default MQTT buffer size on the STM32 side. Here are a few suggestions you can try that may resolve the issue:
- Increase the MQTT Output Buffer: In STM32CubeMX, navigate to the LwIP middleware settings and increase the MQTT output buffer size (try setting it to 1024 bytes or more).
- Adjust LwIP Memory Settings: Increase MEM_SIZE (e.g., to 10 * 1024) and possibly other buffer-related parameters like PBUF_POOL_SIZE and TCP_SND_BUF, which control how much memory is available for networking.
- Ensure ASCII String Length Fits: Make sure the ASCII string generated from your number vector does not exceed the buffer size; longer strings will silently fail to transmit if they overflow the buffer.
- Recompile the Firmware: After making the above changes in STM32CubeMX, regenerate code and recompile the project so the new memory settings take effect.
- Use Debugging/Logs: If available, enable serial or RTT logs to see if buffer overflows or publish errors are happening on the STM32 side.
These changes should help the STM32 handle larger payloads and allow longer vectors to reach Node-RED successfully.
I hope this helps.
