I have a 2560 that I've been working with for a while (over a year for sure), programming it with an avrisp mk2. No issue this whole time, then suddenly, a couple of days ago it starts failing with

avrdude: verification error, first mismatch at byte 0x0002
         0x01 != 0x95
avrdude: verification error; content mismatch

And very obviously not flashing (there's logic that blinks the LED on boot, and the LED isn't blinking anymore).

The first time this happened, the board appeared completely dead - the programmer wouldn't recognize it, and refused to flash it. After a few days and magic it started recognizing it again, and going through the motions of flashing my firmware, but the verification error persists. The location of the error hasn't changed, nor has the two values (0x01 vs 0x95).

Any ideas what this could be?


Still don't know why, but now have a fix. Re-running the 'Burn bootloader' command from Arduino allowed me to then burn my firmware. Not sure if the issue is with fuses somehow being changed, or what, but this seems to have fixed the issue.

One more fun fact - I tried the same thing on a brand new Mega - same effect. First trying to burn my firmware resulted in a verification error (at a slightly different address), then burned bootloader and re-burned my firmware successfully. Wondering if an update to boards.txt or avrdude came through and changed something.

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