I already broke one of two, so ordered five more
They're cheap.
Setup logic - if 4-bytes area at offset 190h of the very first sector is empty (zeroes) i consider it's safe to write there.
If you press "w" in setup - it writes "90h" (as identifier), floppy config byte, bios config byte and a checksum.
If some other data present in that area - BIOS will warn about that and write nothing.
Next time, if id is there and checksum is ok - settings are loaded.
I've also added test mode - 'a' applies settings, but does not write them.
Setup also uses two bytes in reserved bios data area, but as i already use some for floppy emulation - i guess that's ok.
Floppy setup logic may seem somewhat strange, as as i wanted not to change original code much.
So, floppy emulation is auto-on if floppy 0 (A) is set to None and flash drive is present on boot - it's like that was before.
If it's set to some value - original int 13h will work, trying to use real FDC.
If you set floppy emulation to "enforced" - emulation will always be on for drive 0 (A), regardless of drive presence and disk type.
I plan it to return drive type set in floppy config, but didn't get to that so far.