SPI bridging external MCU

[pedrogmnzmr]

Hello everyone,

I'm working on a project where I haven't chosen my LoRa device yet, but let's assume I'm using a Heltec ESP32 LoRa V3 to explain my doubts. My goal is to integrate this LoRa board with a Blues Swan (based on STM32), which handles the user interface of my device, by connecting them via SPI.

The idea is as follows:

• The Heltec, using Meshtastic, communicates over LoRa.

• At the same time, an SPI connection is established with the Blues Swan to exchange messages: the Heltec would receive LoRa messages and forward them via SPI to the Blues Swan, and the Blues Swan could send commands or messages via SPI that the Heltec would transmit over LoRa.

My main questions are:

• Has anyone implemented or knows of a project that performs a similar integration, using the Heltec ESP32 LoRa V3 with Meshtastic and another MCU (such as an STM32) through SPI?

• What hardware and firmware considerations should I take into account, especially regarding SPI configuration (for example, implementing the ESP32 as an SPI Slave) and integrating that communication with the Meshtastic stack?

• Would you recommend any specific protocol for data exchange (headers, checksums, notifications, etc.) or even consider alternatives like UART/I2C that might simplify the implementation?

I appreciate any suggestions, experiences, code examples, or references you can share.
Thanks in advance for your help!