A while back I posted about a flash corruption problem with an 877.  I found the problem.  You've
probably already guessed the answer: it wasn't a flash corruption problem at all.  It was an
EEPROM corruption problem.  And as you've probably guessed, it was a software problem, not a
hardware problem.  The thing that threw me was a rather flaky error message from an otherwise very
reliable programmer (Needham's EMP-11).  The EMP-11's verify checks both the flash and EEPROM
against the hex file images, but reports an EEPROM discrepancy as "low voltage verify failed."  Of
course, in the "fine print" (the log display that usually doesn't say anything of importance), it
always showed the error as occuring at location 4200, which gets mapped from bytes to words as
2100, which is of course the EEPROM on an 877.  I just didn't notice it.

OK, I only wasted about 4 hours (spread over a few weeks of shot-in-the-dark testing) tracking
this down.  I don't think it really compares to the 1 hour or so I spent 21 years ago trying to
figure out why a software change I made to a Z80-based jukebox controller managed to crash
everything.  It was just by chance that the CPU chip sitting on the bench caught my eye.  And it
was a rather unconscious process that then directed my eye toward the empty CPU socket on the
controller board...

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