Bit rate calculation for CAN FD

[nitinverma]

We are using s32k144 evaluation board.

Currently we are using standard CAN with 500 Kbps. 

/* Macros for CAN_Baudrate setting */
BAUDRATE_PROPSEG = 4u
BAUDRATE_PHASESEG1 =  7u
BAUDRATE_PHASESEG2  = 1u
BAUDRATE_PREDIVIDER = 0x00u
BAUDRATE_RJUMPWIDTH = 1u

This setting is working well.

But now we need to use it for CAN FD with data phase as 2 Mbps. Please let us know what values we need to pass for the above parameters.

Thanks

Nitin

[nitinverma]

clock used for the CAN engine is oscillator clock with 8Mhz frequency

[PetrS]

Yes, you can get some setting with the link you provided, but it does not follow basic rules given in The Configuration of the CAN Bit Timing. The PHY interface and bus length must be also considered to get proper PROPSEG value, etc.

You can try e.g this simple guide (https://community.nxp.com/docs/DOC-330446) for Standard CAN bit timing calculation.

Regarding the FD bit time calculation; it is recommended to have the same time quanta length for the data phase and set the sample time somewhere in the middle of the data bit time.

For the 8Mhz protocol clock and your desired 2Mbps for data phase you do not get valid setting. Minimum time quanta is 5, while with 8Mhz clock you get only 4 time quanta per bit. You need to increase protocol clock to be able to have 2Mbps data phase.

For the example link; I see the file within this thread….

BR, Petr

[nitinverma]

Thanks for the help. But we are not able to see the attached "S32K144_FRDM_CAN_FD_Demo_RevC.zip". Could you please upload this again.

[PetrS]

here it is again...

BR, Petr

[guenter_loettrich]

Hi Petr,

would it be possible to provide a specialized CAN-FD bittiming calculator?

There is AN5408 available for clock calcualtions on S32K but unfortunately the FlexCAN module is not considered.

Would be really helpful if that one could be enhanced for standard CAN and CAN-FD clocking calculations.

br

Guenter 

[PetrS]

Hi Guenter,

yes, I am planning to create some document/excel this year, but not sure how fast I will be. We have quite enough work (Cases, community etc) in past days/weeks/months.

The AN5408 does not deal with the CAN timing, only provide module/protocol clock.

BR, Petr

[nitinverma]

Thanks Petr, Now we are able to see the attached file, may be there was some browser issue.

[nitinverma]

We are still not able to see or download the attached zip file. Could you please mail us the zip file at nitinkumar.verma@tcs.com 

[ivadorazinova]

Hi Nitin,

Strange issue, after ctrl+f5 is still not visible? What browser are you using?

I cannot reproduce it on my side.

please could you download it from https://community.nxp.com/servlet/JiveServlet/download/850381-1-395567/S32K144_FRDM_CAN_FD_Demo_RevC... ?

Best Regards,

Iva

[PetrS]

Hi Nitin,

Your bit rate setting is not correct, or better does not follow CAN standard. It can work, but it is not CAN standard compliant.

See attached simple example configuring CAN module to send FD message. The bit timing config is dine in InitCAN() function. A 40MHz bus clock is selected for engine clock.  

BR, Petr

[nitinverma]

Hi Petr,

PFA the link from where I got the values for 500 kbps with 8Mhz frequency for standard CAN.

http://www.bittiming.can-wiki.info/ 

Here the device I have selected as NXP(Freescale)FlexCAN, and got the following mentioned values.

Now, I need the values for CAN FD with data phase as 2mbps and clock is 8Mhz. As per your reply I did not find any attached example,Can you please send it once again.

Thanks

Nitin

[raresvasile]

Hi Nitin,

What is clock is used for the CAN engine(PE clock) ?

Rares

[nitinverma]

clock used for the CAN engine is oscillator clock with 8Mhz frequency