FCEUmm does not save in game

[chromfuoco]

FCEUmm-libretro seems not to correctly handle in-game save (SRAM).

Steps to reporduce:

• load zelda1 with FCEUmm core
• register a new save within the game at start screen
• get the sword, go up, kill an enemy, get 1 coin, then get killed
• choose save option
• now if you die again, quit and try to load, you'll find the save file hosted in SRAM and usable, though the SRAM is not flushed to the filesystem on the host system
• clean exit the emulator
• go to the saves path on the host system (can be the roms path or a dedicated path)
• find the zelda.sav (or whatever your rom is called), edit in an hex editor: the file is empty
• I have found that at times the emulator does not write the file at all on the filesystem

On exiting Retroarch, log shows no errors:

[INFO] [SRAM] Saving RAM type #0 to "/home/user/.config/retroarch/saves/Legend of Zelda, The (USA).srm".

Tried the same exact workflow with QuickNES and the above issue is not present

Tried in Linux, Retroarch 1.22.2, FCEUmm SVN 3a84a6f
Same ahppens in Batocera with Retroarch 1.22.2 and FCEUmm SVN63643ba

[chromfuoco]

Found out that the issue is header dependant. Regardless of header 1.0 or 2.0, if the header reports wrong or unexpected values for SRAM, the .sav file is affected. Though there's no trace of this in the log. More verbose log in these cases may be useful