This topic should not be marked as SOLVED as none of the suggestions worked for me.
After a whole day trying my solution for the following ERROR
failed to switch to bootloader (invalid address?): No such device or address
This occurred via the Arduino IDE and using the Onion Command Line
My hardware is Original Onion Omega + Original Arduino Dock
(Any communication with Onion results in "We suggest you upgrade to Onion2")
Anyway I eventually found a very concise instructions @ [https://onioniot.github.io/wiki/Tutorials/Arduino-Dock/Initial-Setup](link url)
It would appear that it must be configured by burning a new bootloader the very first time.
The second method worked for me i.e. Using the Omega + Expansion Dock with the Arduino Dock ICSP Header
And after that I was able to use the Arduino IDE to program the Arduino Dock.
Now the question is can I communicate via the Onion and the Arduino Dock i.e can a program on the Onion use the Arduino I/O Pins?
And can the two communicate via Serial?