topic How to Calculate FlexRay Header CRC in S12 / MagniV Microcontrollers

How to Calculate FlexRay Header CRC

yusun — Thu, 08 Apr 2010 02:00:31 GMT

Hi everyone,

We are using MC9S12XF512 to build a FlexRay application. However, we cannot figure out how the Header CRC configured for each message buffer is calculated.

The official FlexRay does give an algorighm, but it looks like that the actual implementation in MC9S12XF512 is different. Because we tried to use that algorithm to calculate the Header CRC, but the result is different from the value given in the sample applications.

Any advice?

Thanks a lot.

Re: How to Calculate FlexRay Header CRC

kwridan — Thu, 15 Apr 2010 02:09:43 GMT

Hi,

The FlexRay protocol specs document (can be obtained from www.flexray.com) contains the algorithm, for the header CRC remember to have the inital values as:

vCrcSize=11;
vCrcInit=[0 0 0 0 0 0 1 1 0 1 0];
vData=[1 1 0 0 0 0 0 0 0 0 1 1 1 0 0 1 0 0 0 0];
vCrcPolynomial=[0 1 1 1 0 0 0 0 1 0 1];

vData as you know is

1 bit 1 bit 11bits 7bits
[syncFrameBit,startUpFrameBit,frameID,payloadLength]

I found that the CRC result in the end was the other way around (LSB was on the left!)

Good luck!

Kassem

Re: How to Calculate FlexRay Header CRC

admin — Thu, 29 Oct 2020 09:40:49 GMT

I found that the CRC result in the end was the other way around (LSB was on the left!)

That's because vData have LSB left, i.e. SY bit is LSB.

Re: How to Calculate FlexRay Header CRC

bobgardner — Wed, 11 May 2016 15:30:17 GMT

The Flexray_CC.c module in the NVC7383 demo code has the header crc calc function in it.