Checksum calculation for MCU & PPM

[Mircea Vasiliu]

Hi!

I've read a posting that the checksums are calculated only using every 32 and 33 bytes. However I used NFree and modified different bytes at different locations and the checksum was always modified.

When I modified a byte +1 and another one -1 the checksum stayed the same (so it looks like an addition checksum).

Question 1: why this difference?

Question 2: if the checksum stays the same as viewed with NFree for a modified MCU or PPM will the FAID still need calculation after flashing?

[||Joe]

Flash checksum is calculated using only every 32. & 33. bytes.
IF these bytes are changed, no matter if MCU or PPM checksum stays same,
FAID must be calculated.

MCU & PPM checksums are calculated from all bytes taken from certain areas.
(PPM1, PPM2...)
And yes, it is an addition checksum.
No spooky algorithms are used.
(Sometimes some XOR or other logic operands are used too.)

[Mircea Vasiliu]

Thx for reply!

Do you happen to know where the checksum is calculated and verified? Is it inside MCU or somewhere else?