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Add a CRC32 over progmem and ESP.checkFlashCRC (#6566)

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* 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.
This commit is contained in:
Earle F. Philhower, III
2019-12-20 14:38:35 -08:00
committed by GitHub
parent 9985a32914
commit 52d84b1ead
7 changed files with 124 additions and 1 deletions
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doc/libraries.rst
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@ -113,6 +113,8 @@ Some ESP-specific APIs related to deep sleep, RTC and flash memories are availab
``ESP.getCycleCount()`` returns the cpu instruction cycle count since start as an unsigned 32-bit. This is useful for accurate timing of very short actions like bit banging.
``ESP.checkFlashCRC()`` calculates the CRC of the program memory (not including any filesystems) and compares it to the one embedded in the image. If this call returns ``false`` then the flash has been corrupted. At that point, you may want to consider trying to send a MQTT message, to start a re-download of the application, blink a LED in an `SOS` pattern, etc. However, since the flash is known corrupted at this point there is no guarantee the app will be able to perform any of these operations, so in safety critical deployments an immediate shutdown to a fail-safe mode may be indicated.
``ESP.getVcc()`` may be used to measure supply voltage. ESP needs to reconfigure the ADC at startup in order for this feature to be available. Add the following line to the top of your sketch to use ``getVcc``:
.. code:: cpp