* Add a CRC32 over progmem and ESP.checkFlashCRC
Automatically embed a CRC32 of the program memory (including bootloader
but excluding any filesystems) in all images in unused space in the
bootloader block.
Add a call, ESP.checkFlashCRC() which returns false if the calculated
CRC doesn't match the one stored in the image (i.e. flash corruption).
Fixes#4165
* Add example that corrupts itself, comments
Show CRC checking catch a 1-bit error in program code by corrupting a
large array, and then return it to clean and verify the CRC matches once
again.
Add comments to the CRC check routine
Clean up pylint complaints on crc32bin.py
* Check linker script for CRC space in bootsector
Add an assertion in the eboot linker file to guarantee that we have at
least 8 bytes of unused space at the end of the boot sector to patch in
the CRC. If not, the eboot link will fail.
* Add note about what to do if CRC check fails
Per discussion with @d-a-v.
When the CRC check fails, you could *try* to do certain things (but may
not succeed since there is known flash corruption at that point). List
a few ideas for application authors.
* Only single, flash/ram friendly crc32() function
* Combine the CRC calc and bin generation in 1 step
Per discussion w/@mcspr, combine the CRC calculation with the binary
generation, removing the additional build step.
