Non-volatile Memory - Data Repositories

This area is intentionally structured in the following way:

╰- quantum
   ╰- nvm
      ├- readme.md
      ├- rules.mk
      |
      ├- nvm_eeconfig.h
      ├- nvm_<>.h
      |
      ├- eeprom
      |  ├- nvm_eeconfig.c
      |  ├- nvm_<>.c
      |  ╰- ...
      |
      ├- <<another provider>>
      |  ├- nvm_eeconfig.c
      |  ├- nvm_<>.c
      |  ╰- ...
      ╰- ...

At the base nvm level, for every QMK core system which requires persistence there must be a corresponding nvm_<>.h header file. This provides the data repository API to the "owner" system, and allows the underlying data persistence mechanism to be abstracted away from upper code. Any conversion to/from a .raw field should occur inside the nvm_<>.c layer, with the API using values, such as structs or unions exposed to the rest of QMK.

Each nvm "provider" is a corresponding child directory consisting of its name, such as eeprom, and corresponding nvm_<>.c implementation files which provide the concrete implementation of the upper nvm_<>.h.

New systems requiring persistence can add the corresponding nvm_<>.h file, and in most circumstances must also implement equivalent nvm_<>.c files for every nvm provider. If persistence is not possible for that system, a nvm_<>.c file with simple stubs which ignore writes and provide sane defaults must be used instead.