I found procedure gatewayTransportInit(), it works great. However, I cannot find a procedure that will enable detection of a network connection at level mysensors. I noticed that disconnecting the network plug or resetting the W5500 (37 pin to ground) changes the device's IP address to 0.0.0.0 - then I call gatewayTransportInit() - but mysensor's library must have such procedures - please tell me how to diagnose ethernet connection.
Just for completeness: the right way to do this is to add the json under ~/.platformio/boards and the other files as described in https://community.platformio.org/t/how-use-a-same-chip-but-with-different-environment/18082/4
IT WORKS
I got a first working version, using an ATmega1284P running on MightyCore 2.2.2 (as soon as I began developement, they switched from Optiboot to Urboot in version 3.0.0, whicht does not include the copy_flash_pages function anymore, but I'm working on a work around there).
Only thing I could not solve is to do a CRC check of the image after download...
You can try it out here: https://github.com/eiten/MySensors/tree/FOTAInternalFlashTest
It's not beautiful yet with much Serial.prints in it, but maybe it helps you if you find errors.
