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Trouble with the CRC unit on STM32F407

Question asked by Nils B on Jan 17, 2018
Latest reply on Jan 30, 2018 by waclawek.jan

Hello everyone

I have some trouble with the CRC unit on my STM32F407 MCU.
Before each time I am going to use it to calculate a checksum, I reset it and after doing so I double check that the CRC data register (CRC_DR) is as what is expected (just 1s, 0xFFFF_FFFF). This is not always the case and I'm confused why.
So far my application, that uses the CRC unit, seems to be working fine. I don't get any false positive errors (i.e. the CRC unit says the checksum was incorrect when it wasn't).
I could just ignore this check and hope that nothing is wrong, but I have a bad gut feeling about doing that (something might actually be wrong).

I speculate that I perhaps there's a timing issue of some sort. That the CRC unit needs a few more clock cycles before its data register has the correct reset value.

Do you have any ideas about what could be wrong?

I would really appreciate any help with this issue.

Best regards


Before I use the CRC unit, I enable the CRC clock by setting CRCEN bit in RCC_AHB1ENR and then I set the CRCRST bit in RCC_AHB1RSTR and then clear it.
I reset the CRC by setting the reset bit in the control register of the CRC unit (CRC_CR).