arduino uno r4

**Is your feature request related to a problem? Please describe.**
I want to use this library with arduino uno r4

**Describe the solution you'd like**
I want to run the example msc_sd on an arduino uno r4

**Describe alternatives you've considered**
Nothing

**Additional context**
Nothing

Start by examining the msc_sd example and how this library targets Arduino boards, then determine what Arduino Uno R4 support requires. Done means the msc_sd example runs successfully on an Arduino Uno R4, with the required compatibility work identified and verified.

Written by the indexing model from the issue text.