SELFUPDATE UX improvements about beeblink

[tom-seddon]

When updating the ROM, SELFUPDATE swaps the old and new ROMs. When all goes well, you end up with the new ROM in the ROM bank, and the old ROM in RAM (hopefully where RTOOL can find it). My thinking here was that if you find any obvious immediate problems, and your BBC B has no other FS, and you've still got RTOOL in the EEPROM/flash bank, you can do *ROM then CHAIN"RTOOL" then P to restore the old version.

I don't think this is actually all that useful though.

[tom-seddon]

Got some corrupted ROM images from toggling the write protect switch while the system was running. Might be cartridge-specific? Anyway, decided to leave this as-is.