RPMsg Not Creating /dev/ttyRPMSG0 on Apalis iMX8 (BSP 6.8.0)

[SruthiSathyan]

Hi,
I am working with the Apalis iMX8 module using the TDX Reference Multimedia Image (BSP 6.8.0) built with Yocto. My goal is to establish communication between Cortex-M4 and Linux using RPMsg.

I have downloaded the SDK for Cortex-M4 from the NXP website and built the rpmsg_lite_str_echo_rtos example application. The application is successfully loaded onto the Cortex-M4_0 processor, and the only output I see on the M4 side is:

RPMSG String Echo FreeRTOS RTOS API Demo...

However, on the Linux side, /dev/ttyRPMSG0 is not created. Running dmesg | grep rpmsg shows:

[ 0.397693] imx rpmsg driver is registered.

Do I need to modify the device tree or provide a device tree overlay to enable RPMsg on Linux? If so, where can I find a working example or the necessary modifications?

[ToradexAI]

Hi, I’m the Toradex AI Assistant. The Toradex Support team will follow up with you shortly!

Did you like my answer?

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Hello,

To enable RPMsg communication between the Cortex-M4 and Linux on your Apalis iMX8 module, you will indeed need to ensure that the device tree is configured to support RPMsg. This typically involves using a device tree overlay to allocate the necessary resources for RPMsg communication.

Here’s a step-by-step guide to help you:

1. Check for Existing Overlays: First, verify if there is an existing RPMsg overlay for your module. This overlay might be named something like rpmsg-imx8.dts.

2. Apply the Overlay: Use the fw_setenv command to set the fdt_overlays environment variable in U-Boot to include the RPMsg overlay. For example:

   fw_setenv fdt_overlays <existing_overlays>,rpmsg-imx8.dtbo
   

   Replace <existing_overlays> with any other overlays you are currently using.

3. Reboot the Module: After applying the overlay, reboot your module to apply the changes.

4. Load the RPMsg Kernel Module: Once Linux has booted, ensure that the RPMsg kernel module is loaded by running:

   modprobe imx_rpmsg_tty
   

5. Check dmesg Logs: Use dmesg | grep rpmsg to verify that the RPMsg driver is registered and functioning correctly.

If the /dev/ttyRPMSG0 device still does not appear, double-check the device tree overlay for any errors and ensure that the RPMsg example application on the Cortex-M4 is running correctly. Also, verify that the memory regions used by RPMsg are not being used by other parts of the system.

I hope this helps you get your RPMsg communication up and running!

Best regards,
Toradex AI Assistant

Please, also check if these links can help you solve your problem:

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[sahil.tx]

Hi @SruthiSathyan,
Yes, there are some modification needed on the device tree, this post should solve your issue.

[SruthiSathyan]

I was able to successfully run the rpmsg_lite_str_echo_rtos example on the Apalis iMX8 and could see data using cat /dev/ttyRPMSG30 &. However, when I modified the transmitted data from the received value to a hardcoded one, I stopped receiving anything on cat /dev/ttyRPMSG30 &. Interestingly, I can still see the received message in dmesg.

My ultimate goal is to run a CAN program on Cortex-M4 and transfer the CAN data to Cortex-A via RPMsg, so that a Qt application running on Linux can access this data.
How should I proceed to resolve this issue?

[sahil.tx]

Hi @SruthiSathyan

@SruthiSathyan

However, when I modified the transmitted data from the received value to a hardcoded one, I stopped receiving anything on cat /dev/ttyRPMSG30 &

Sorry, can you explain more.
Where did you modify ?
Please check the rpmsg_lite_str_echo_rtos source code for further debugging.

Next you can test CAN demos and then try to send CAN data via RPMSG virtual port.

[SruthiSathyan]

For working on CAN on the cortexM4 processor of apalis imx8:
1.Device Tree:
Do I need to modify the Linux device tree to use CAN from the M4 core, or is it accessible if unused by Linux?
2.Classical CAN:
The SDK only provides FlexCAN examples. Can it be configured for classical CAN (11-bit, no CAN FD)? If so, how?
3.CANL / CANH Pins:
Which physical pins correspond to CANL and CANH for use with M4? Which FlexCAN instance maps to which pins?