Backup RAM (SRAM)
Retained data validation
Be sure to validate the data before using it. The data is reinitialized to default values on cold boot, however there are cases where the data could be invalid. For example, if the device is reset during the process of writing data.
Storing the data in a struct and using a CRC or hash is a good defensive technique. It can also gracefully handle adding new retained variables, or changing the size of retained variables.
When doing a user firmware update, retained memory is typically preserved, but in addition to explicit changes in the data your retain, the compiler may also relocate retained data unexpectedly. Using additional sanity checks can help prevent using invalid data.