Flash via Serial or OTA fails but OK via DFU

[UMD]

@ScruffR,

Spooky thing is that I had spotted this gem from @bko (the bit that starts "One thing that trips ..." last night:

Unflashable after I2C

Hi @ddres0605 Please see the other thread about the CCS881 where you are not calling Begin on the sensor library for the i2c sensor. If you are having trouble there are two things to try: Safe mode: if you can get into safe mode you can often fix problems. DFU mode and use the CLI or dfu-util to flash new firmware One thing that trips people up is that the web IDE will not flash firmware compiled against a wrong version of system firmware for you device. This can make it look like nothing …

which got me thinking - the evidence (returning to safe mode) was pointing to what @bko was saying.

So tried this:

Flashed firmware 0.8.0-rc.1 via DFU (ie back to a known position)
Safe Mode
Recompiled app against 0.8.0-rc.1 to and flashed new app v3.10.0 via OTA
Safe mode <=== BAD

Then tried @ScruffR suggestion:

Flashed bootloader-0.8.0-rc.1-photon via SERIAL
It reset (good) to breathing CYAN! But app was not running
Flashed flashed new app v3.10.0 built against 0.8.0-rc.1 via OTA
Breathing CYAN and app running! <=== SUCCESS

Lessons:

• Beware of system and app mismatch
• Beware of system and bootloader mismatch
• Back to safe mode is indicative of a mismatch
• When saving app binary files, include the system version, eg "0.8.0-rc.1+APP-3v100.bin"
• Persistence
• Ask for help!

So, case closed with thanks to the team!