topic Re: CAN-FD frames loss on IMX8QXP in i.MX Processors

CAN-FD frames loss on IMX8QXP

_Guillaume_ — Tue, 09 Dec 2025 10:17:23 GMT

Hello,

I am using MCIMX8QXP-CPU board with MCIMX8QXP-8X-BB. I have some trouble with can-fd frame with data rate of 2Mbit/s. All was ok with "classic" CAN and CAN-FD 1Mbit/s, but with 2Mbit/s I had a lot of frames loss. I know my input signals are not perfect because they come from contactless CAN bus reader and I observe some noise. But I am able to read all frames without issues with CAN recorder like Kvaser, pcan, etc.

I read on another topic that CAN controller clock could have an impact on that frame loss ?
In my config I have 40MHz CAN clock.
I tried to modify it, but didn't succed to find how to do this. I firstly try to modify device tree and then read that it could also be in firmware (scfw). For info, i uses yocto to built the system

Do you think that this clock could be the reason of my frame loss ? If yes, how do I have to update it ?

Thank you for your help.

Re: CAN-FD frames loss on IMX8QXP

Bio_TICFSL — Tue, 09 Dec 2025 14:03:12 GMT

Hello,

The issue may indeed be related to the CAN controller clock configuration. For CAN-FD operation at higher data rates (2Mbit/s), clock precision becomes critical. With your current 40MHz CAN clock and when using contactless CAN bus readers that introduce some noise, timing tolerances can become more restrictive.

There are two potential approaches to resolve this issue:

1. **SCFW Modification**: The CAN controller clock is configured in the System Controller Firmware (SCFW). You would need to modify the SCFW configuration files to adjust the clock settings. This requires rebuilding the SCFW.

2. **Device Tree Modifications**: You can also try adjusting the CAN timing parameters in the device tree. For CAN-FD operations, you may need to enable Transmitter Delay Compensation (TDC) which is particularly important for data rates above 2.5Mbps.

For your specific case with contactless CAN bus readers introducing noise, you might benefit from adjusting the bit timing parameters to be more tolerant of signal variations. This can be done by modifying the propagation segment values in your device tree configuration.

Since you're using Yocto, you can implement these changes through your device tree overlays or by patching the kernel source directly.

Regards

Re: CAN-FD frames loss on IMX8QXP

_Guillaume_ — Fri, 12 Dec 2025 11:09:03 GMT

Thank you for your feedback.

I try both options

1) SCFW Modification:

I successfuly generated the firmware scfw_tcm.bin file

Then, inside my yocto project i have theses generated files :

bl31-imx8qx.bin bl31-imx8qx.bin-optee m4_image.bin mkimage_imx8 mx8qxc0-ahab-container.img mx8qx-mek-scfw-tcm.bin scfw_tcm.bin soc.mak tee.bin u-boot-imx8qxp-mek.bin-sd u-boot-spl.bin-imx8qxp-mek-sd

When i use the imx-mkimage tool, i have to copy theses files :

bl31-imx8qx.bin, u-boot-imx8qxp-mek.bin-sd, scfw_tcm.bin and mx8qxc0-ahab-container.img

to my imx-mkimage tool and then when i try to generated the new binary i got this error :

include misc.mak

include m4.mak

include android.mak

include test.mak

include autobuild.mak

include alias.mak

make[1]: *** Aucune règle pour fabriquer la cible « mx8qxb0-ahab-container.img », nécessaire pour « flash ». Arrêt.

make: *** [Makefile:26 : flash] Erreur 2

I see that yocto generate mx8qxc0-ahab-container.img and not mx8qxc0-ahab-container.img, so i also try to rename it, but i got the same issue.

2) I successfully modify my device tree and i can see new clock frequency on my board.

Then I try to update the timing of my controller with iproute2 commands but my new settings aren't applied.

You wrote : you may need to enable Transmitter Delay Compensation (TDC), I didn't find any documentation on that. If I understand timing parameters can be directly set on device tree ?

Re: CAN-FD frames loss on IMX8QXP

_Guillaume_ — Wed, 17 Dec 2025 11:29:09 GMT

Hello,

I still have my issue: canfd frames loss.

As I said, I successfully update the controller clock to 80Mhz. But it's not enough.

I am not able to modifying the timing. I don't know exactly how I have to do it ? As for enabling the Transmitter Delay Compensation (TDC), I didn't find documentation on it for imx8.

Thank you for your help,

Guillaume