bperrybap:
fungus:
The only thing I can think of is a batch of chips got sent out with incorrect fuse settings. The setting allowed people to overwrite their bootloaders. Rewriting the bootloader would set the fuses correctly, preventing them from being able to reproduce the problem.But like I said earlier with the older bootloader,
it was possible to enable WDT and create a situation where it was not possible
to upload a new sketch using "normal" means.
When the bootloader was re-written it also removed the sketch and things worked as "normal" again.-- bill
Well the problem symptom with using WDT with older bootloaders was well know even back them. And yes reburning the bootloader would 'fix' the problem, but also unless the time-out value was very short one could recover without reburning the bootloader by holding down the reset button, then upload a different sketch that didn't use WDT and only release the reset button when the compiler was done and AVRDUDE was called by the IDE to upload the new code. And even back then there was a bootloader modified by ADAFRUIT that was available and worked with WDT, if one wanted to use it.
The problem I was writing about was just people reporting that they could no longer upload at all (and not using any WDT commands) and just reburning the bootloader got them working again. Now it was and is still hard to do good troubleshooting analysis just going by user reports and not first hand experience, but again it was a pretty common report that many users had to reburn their bootloader to return functionality to their chip and the root cause was never really solved, at least to my satisfaction. I personally have never had to reburn a bootloader to solve a problem, just to upgrade for better performance like ADAFRUIT or UNO bootloaders.
So again, with WDT problems aside, is it possible to write and upload a sketch via the IDE that will prevent ever being able to upload a different sketch, as was reported by users of pre Uno boards? Also this is not the problem seen with the very first release of the UNO board with using the AVR USB serial converter chip that if the running sketch started right up sending data via serial commands that the AVRDUDE upload would fail due to choking on the incoming data stream. That was fixed by a quick update of the Uno's bootloader code as I recall.
Lefty