Why UART2 cannot be used on M7

SOM module is Verdin iMX8M Plus Q 4BGWBIT V1.1A
Carrier board: Mallow Carrier Board V1.1A
Linux BSP: v6.6.0, Linux kernel: v5.15

In order to output debugging information from M7 to UART2, I try to use it by changing UART4 to UART2, but the code crashes due to a hard fault.
When I looked into the cause, I found that UART2 in the boot code was set to the domain area used by Linux.

  1. Why is UART2 set to the domain area used in Linux?
  2. In my opinion, the UART port for debugging of the A53 should be set to 2, but the setting is set to 3. Is there a reason why it is not assigned to UART2?
    Is there any problem if I assign UART port number 2 for debugging of A53?
  3. Is the reason why UART2 is set to the domain area used in Linux related to security? If so, please explain why.
    thank you.

Hello, This is Jung Hyun Jeong from Toradex.

We are currently investing your issue.

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Jung Hyun Jeong

Our product is designed according to this table for UART connections.

Please use this guideline for your design.
Thank you


Jung Hyun Jeong

Hello Jung Hyun Jeong.
UART_2 was not available in cortex-M, so I checked and found that domain w0 was set in TF-A.
So, after deleting the part set to domain w0, it could be used normally in cortex-M.
Is there a reason why TF-A set domain w0? Are there any features that UART_2 uses regarding security?
Thank you.


  • UART4 was the standard UART for cortex M debugging on the iMX8MP, but this had to be changed when we had to remap the interfaces for the wifi module.

  • All current and future versions of the iMX8MP use UART4 for the bluetooth communication, and this is the reason this interface is not available anymore for debugging.

  • Regarding the problem that UART2 is not working out of the box on the cortex M7, this is a known issue being tracked within our R&D.

At this moment, this serial mapping is hard-coded in this setting from NXP.

Thank you


Also I emailed you whether you can share company info for this support. So that, we can help you more in depth in future.

Jung Hyun Jeong