Hi,
I have a couple of questions. I´m using a MPC5748G and I want to change the bit timming when using CAN-FD mode.
Currently I have CAN-FD working with 500kbps arbritation and 2000Kbps Data Phase working.
Now I want to change the sample point to make some tests.
Is there any document like "FlexCANbitTiming.pdf" but for CAN-FD?
I understood from Reference Manual that CAN-FD arbitration bit timing is affected by CAN_CTRL1 or CAN_CBT and data phase is affected only by register CAN_FDCBT, right?
As far I understood, the CRC on the register is filled at TX: "This register is updated at the same time the Tx Interrupt Flag is asserted."
Is the CAN module checking also the CRC of received frames? Is there a code to calculate CRC of CANFD frames of a non-iso can-fd?
Thanks in advance,
Antonio
antoniograu, you might want to look at this topic as well, especially answer from lukaszadrapa:
https://community.nxp.com/thread/377680#comment-575999
CRC calculation of MPC5748G is compliant up to certain version of CAN-FD specification, for later specification, you(we)'ll need newer cut of the devices...
Hi,
Q: Is there any document like "FlexCANbitTiming.pdf" but for CAN-FD?
A: unfortunately not. You should use an info stated within Reference Manual or CAN-FD specification.
Q: I understood from Reference Manual that CAN-FD arbitration bit timing is affected by CAN_CTRL1 or CAN_CBT and data phase is affected only by register CAN_FDCBT, right?
A: Yes, you are right.
Q: Is the CAN module checking also the CRC of received frames? Is there a code to calculate CRC of CAN-FD frames of a non-iso can-fd?
A: There are different CRC polynomials for different CAN frame formats.
- CRC_15 … used for all frames in Classical CAN format.
- CRC_17 … used for frames in CAN FD format with a data field up to 16 bytes long.
- CRC_21 … used for frames in CAN FD format with a data field longer than 16 sixteen bytes.
The receivers use the same polynomial to calculate the check sum from the bits as seen on the bus-lines. Thus when receiving a message, FlexCAN decodes EDL and DLC to select the adequate CRC polynomial to check for a CRC error.
BR, Petr
Hi Petr,
thanks for your answer.
About the CRC Thema for CAN_FD frames with BRS (Bite Rate Switch) activated:
I´m sending CAN-FD with fixed DLC =15 from FlexCAN1 to FlexCAN2, 3, 4 and 5. So CRC21 will be used.
I can see the register CAN_FDCRC of CAN1 is updated every time a frame is sent.
What I want is to compare the CRC_FD from my CAN1 with the CRC_FD received on the other channels.
My question is:
Is FlexCAN module only showing CRC or CRC-FD errors at Transmission time? Is it possible to check CRC errors at receiving?
Thanks!