Incorrect CRC32 on STM32F429

[xobs]

Description

I'm seeing what I believe is an incorrect CRC32 calculation on an STM32F429. I can't explain why this would be, except perhaps that they use the reflected version when providing the CRC to the user.

Expected behaviour

I'm working on understanding a binary firmware. It contains this code:

  Peripherals::CRC.CR = 1;
  Peripherals::CRC.DR = 0xf407a5c2;
  uVar1 = Peripherals::CRC.DR;
  if (uVar1 != 0xb5e8b5cd) {
    do {
                    /* WARNING: Do nothing block with infinite loop */
    } while( true );
  }

With the current implementation of STM32F4_CRC, the resulting value is 0x74EA5CA6. If I instead reflect both the inputs and the outputs, I get the matching value of 0xb5e8b5cd:

            crc = new CRCEngine(CRCPolynomial.CRC32, init: 0xFFFFFFFF, xorOutput: 0, reflectInput: true, reflectOutput: true);

Additional information

I can verify that the output of https://github.com/dimmykar/stm32-crc32-calculator matches what I see -- namely that the CRC32 of 0xF407A5C2 should evaluate to 0xb5e8b5cd.

Has this ever been validated against real hardware? If so, something isn't quite adding up. If not, then it can be fixed in the model.

Do you plan to address this issue and file a PR?

It's an easy enough fix, but if there is hardware and tests that already use the existing behaviour then I'd rather not touch it and keep using my modified model.

[mszprejda]

The fix from renode/renode-infrastructure#97 is merged. Thanks for the contribution!