EEPROM library flushes data on each write

[me21]

Is your feature request/improvement related to a problem? Please describe.

According to the source code, EEPROM.write assigns value to EERef: (EERef(idx)) = val;.
This calls EERef::operator= which in turn calls eeprom_write_byte.
On devices without actual EEPROM, it calls eeprom_buffered_write_byte and eeprom_buffer_flush which erases and rewrites the whole page of flash leading to excessive wear.

Describe the solution you'd like

I like the approach taken in the alternative implementation: https://github.com/rogerclarkmelbourne/Arduino_STM32/tree/master/STM32F1/libraries/EEPROM
Not only it erases the flash page only when needed, it avoids the buffer in RAM by writing half words directly to the free space on the flash page. The new variable value is written to the free space, not overwriting its previous value, thus avoiding the need for flash page erase.
On another hand, that implementation writes a header for each stored variable, halving the available space, whereas this implementation just gives access to the raw contents of the flash page.
Maybe it's possible to add a pair of function like disableAutoFlush and enableAutoFlush, documenting that each flush causes flash page erase cycle?
Or should I use eeprom_buffered_write_byte and eeprom_buffer_flush directly? Then EEPROMClass is not very much usable with respect to writing data - as I said, each byte change will cause flash page erase.

[fpistm]

For me it is covered by #333

IIWR Writing to flash one or more bytes required to write full page.
Do not hesitate to provide a PR if you think having a better solution. 😉

[me21]

I see, so your proposal is to use eeprom_buffered_write_byte(addr, value); instead of EEPROM[addr] = value;.
It's just that EEPROMClass currently has not much value as EEPROM.put(addr, my_struct); will cause as many page erases as there are changed bytes in my_struct since the last write.

[fpistm]

Here an example made by a contributor:
https://github.com/stm32duino/STM32Examples/blob/main/examples/NonReg/BufferedEEPROM/BufferedEEPROM.ino