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What is "Fix compatibility test checksum" ?
In EDC16/17 ECUs the memory is parted in blocks, which have different functions. These functions
are based on each other and so the blocks are depending on each other. The lowest level is the operating
system, above is the user program and at last the map data.
These blocks are linked by a data structure that is supposed to ensure that the blocks also match each other.
So, for example, map areas can be reprogrammed without having to erase and program the rest. If the ECU program is reprogrammed,
also the map areas must be reprogrammed.
The name of this data structure is "Compatibility Test Checksum".
It is not checked on all ECUs. New:
Instead of calculating the new result, a correction is made to an address at the end of the map area so that the real result of the compatibility test checksum is the same for the original and the version.
This also eliminates the need to synchronize the result with other blocks.
This is particularly useful for OBD2 programming, since most of the time only the map area is programmed.