Best practices for parameter storage?

[ccrome]

What are the best practices for storing parameter information that can be shared between the bootloader and application?

For example, some typical stuff I'd like to store are:

Fixed, unchangeable data.

• board build date
• build factory
• serial number

Variable Data

• board settings and/or data that might be collected at runtime.

[hathach]

uf2 has a specs for this called cf2: https://github.com/microsoft/uf2/blob/master/cf2.md . I usedd it a bit in nrf52 bootloader but haven't done so for tinyuf2 just yet https://github.com/adafruit/Adafruit_nRF52_Bootloader/blob/master/src/boards/feather_nrf52840_express/pinconfig.c