JLink is conflict with FRDM-K64F USB port

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JLink is conflict with FRDM-K64F USB port

Contributor II


I'm trying to debug FRDM-K64F host msd command bm project with a JLink EDU and a U-disk.

There are two USB ports, SDA USB and K64F USB.

If the power cable linked to the SDA USB and U-disk linked to K64F USB, the MCUXpresso will show an error that couldn't connect to the target when debugging with JLink EDU as the picture shown.


If power cable linked to the K64FUSB and U-disk linked to SDA USB, JLink Edu works and could debug the project. However, the demo project couldn't detect the U-disk and no attached eventBit flag is set.

Could you please help to explain this and how could I debug the USB demo project with JLink Edu?

Besides, I know the other debug option LinkServer works. But I have to use JLink for future development.


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NXP TechSupport
NXP TechSupport

Hi silent-dawn@outlook.com 

  You are using the  FRDM-K64F on board JLINK debugger or the external JLINK debugger?

  If you are using the external JLINK debugger, you need to check, your on board debugger is not the JLINK firmware. Otherwise, the on board debugger may conflict with your external debugger.

  Please check the tool situation at first.

Wish it helps you!

If you still have questions about it, please kindy let me know.

Best Regards,



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Contributor II


Changing to segger openSDA firmware will works.


After testing and searching, I guess it should be the problem of openSDA firmware. I get this idea from the link Cannot debug FDRM-K64F via J-link. 


It shows I need to power the board with K64F USB port when using external JLink EDU if using mbed/CMSIS-DAP which is come as default configuration of the board.

So I think I need another openSDA firmware which supports to power the board with SDA USB port. I know that segger provides another openSDA firmware as the link https://www.segger.com/products/debug-probes/j-link/models/other-j-links/opensda-sda-v2/ . As the description, I think it should support it.

And I follow another tutorial on how to download the segger openSDA as the link Install OpenSDAv2 Firmware on FRDM-K64F Board- MATLAB & Simulink . Please pay attention to the second step that you need to press the reset button firstly before connect to PC.

Finally, it works! The power cable is connected to SDA USB port and U-disk to K64F USB port.

Still confused

I still do not know the details about these two openSDA firmware and why it acts like this. If anyone knows and be likely to share it. Really appreciate it.

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