Just so you know, installing the tiny branch for the Atto84 (as per your instructions) will cause Arduino IDE 1.8.10 to overwrite the file that contains artemis board definitions with a file that doesn't contain them.
And found it to be true - at least sorta. Although the installed Apollo3 files aren't modified or removed the package index JSON file was replaced. This happened because the filename was the same in both the master and tiny branches. Not sure why Arduino chose to keep the Atto84 version over Apollo3 (it happened no matter what order I placed the URLs in the additional boards manager URLs field).
Without the package index JSON file to guide Arduino to the installed package it appears that the package is no longer installed.
Solutions
Different file names in different branches. This is the solution that I have temporarily employed, but I don't prefer it to other options. In the tiny branch I changed the filename to package_sparkfun_tiny_index.json. The package name on the inside is still 'SparkFun' so the packages still get put together.
Merge all the branches. If we don't like the idea of having several different URLs that customers need to put into their preferences then we could merge all the branches together. However in that case the customer has to download and install packages for all our boards just to get one. I don't like this idea personally.
Maintain package index files in different places. For example the Atto84 package could live with the Atto84 repo and the Apollo3 packag index could live inside the Apollo3 Arduino repo. They would still need to have unique names (like option 1) but (at east to me) it would feel a little more logical that they have different names.
I was investigating this comment:
And found it to be true - at least sorta. Although the installed Apollo3 files aren't modified or removed the package index JSON file was replaced. This happened because the filename was the same in both the
masterandtinybranches. Not sure why Arduino chose to keep the Atto84 version over Apollo3 (it happened no matter what order I placed the URLs in the additional boards manager URLs field).Without the package index JSON file to guide Arduino to the installed package it appears that the package is no longer installed.
Solutions
tinybranch I changed the filename topackage_sparkfun_tiny_index.json. The package name on the inside is still 'SparkFun' so the packages still get put together.