mqtt_esp8266_uart_bridge

Main repository at: https://github.com/wiredlab/mqtt_esp8266_uart_bridge

Bidirectional bridge between a UART TX/RX port and MQTT topics.

Target is the ESP-01s board using the ESP8266.

Features

• Bytes published to …​/stdin are sent out of the device UART’s TX pin.

• Bytes received on the device UART’s RX pin are published to …​/stdout.

• Device periodically publishes telemetry to …​/status.

• Device subscribes to …​/control for commands.

MQTT topics

The base topic is constructed as:

• PREFIX = MQTT_TOPIC_PREFIX + my_mac

Caution

Pay attention to the / separators!

The device uses the following subtopics for various purposes:

• PREFIX/status — MCU publishes JSON-formatted telemetry here. See pub_status_mqtt(state) for the contents.

• PREFIX/control — MCU subscribes to listen for configuration changes. (ignored for now)

• PREFIX/stdin — MCU subscribes and passes payload as-is out of TX pin. MQTT handles the variable-length binary payload already. There is presently no extra framing added to the byte stream.

• PREFIX/stdout — MCU publishes frames received on its RX pin. A frame is presently: bytes received within CHAR_TIMEOUT of each other and ended with a \n character (0x0A), which is not passed on.

TODO

• There needs to be a better way to extract payload frames from the UART RX receive port. Presently it ignores \r, uses \n as a payload terminator (not passing on the \n to MQTT), and publishes after a timeout if no \n has been seen yet.

  • Consistent Overhead Byte Stuffing is a candidate.

  • But, it should be something that includes a start-of-frame also (in both directions), since the UART TX is also used for random debugging printf’s. Open to your suggestions!