CDC COM Port Stops Working Without J-Link RTT Viewer on Custom nRF52840 Board

[manoj_patil]

Hello,

We are using the nRF52840_CKAA_R7 package of the nRF52840 on our custom board. The USB pin connections are designed based on the nRF9160-DK's nRF52840 reference.

I am trying to run the console sample from the nRF Connect SDK (NCS) on this custom board. However, the sample doesn't seem to work as expected.

Details and Observations:

1. The USB pin connections on our custom board match those of the nRF9160-DK's nRF52840 setup.
2. The sample builds and flashes successfully without any errors.
3. When I use the J-Link RTT Viewer, the CDC COM USB port works as expected, and I can see the output through the USB connection.
4. However, when I disconnect the J-Link RTT Viewer, the CDC COM USB port stops working entirely, and no output is available over USB.

Troubleshooting Steps Taken:

• Verified the USB pin configurations in the device tree files.
• Checked the power supply to the USB port on the custom board to ensure it remains active after disconnecting J-Link RTT Viewer.
• Confirmed that the USB initialization happens in the firmware.

Suspected Issues:

I suspect there might be some missing configurations or initialization steps that are causing this behavior. For instance:

1. The USB device tree bindings or pin configurations might need adjustments specific to our custom board.
2. The firmware might not be correctly managing the USB power or initialization when the J-Link RTT Viewer is not active.

Question:

What changes or additional configurations should I make in the code to ensure the USB CDC COM port works independently of the J-Link RTT Viewer?

If there are any logs or outputs you need me to share, please let me know.

Thank you for your help!

[Einar Thorsrud]

Hi,

Is it only USB CDC that does not work when not debugging, or does the device not seem to be oprrating at all? (for instance, if you toggle the LED in the application, do you see it toggling)? If debugging is needed in order to run the application, is it worth checking that you have not enabled VDDH in the board files. Also, consider disabling the RTT console / shell backend.

Also, which SDK version are you using, and is it this console sample you are refering to, or another?

[manoj_patil]

We have checked all the peripherals and the application, and they are running well. However, we are still facing the same problem as before. Could you guide us on how to enable VDDH in NCS v2.6.1?

[Einar Thorsrud]

Hi,

I think you can ignore my comment about configuring VDDH. As long as VDDH is shorted to VDD, andy VDDH related config should be irrelevant. But it could be worth making sure BOARD_ENABLE_DCDC_HV is not enabled (for instance by explicity setting CONFIG_BOARD_ENABLE_DCDC_HV=n. If that does not help, we should look at other potential causes of this issue.

[manoj_patil]

I got my solution by using the following prj.conf configurations:

# CONFIG_CLOCK_CONTROL_NRF_K32SRC_SYNTH=y
# OR
CONFIG_CLOCK_CONTROL_NRF_K32SRC_XTAL=y
# CONFIG_CLOCK_CONTROL_NRF_K32SRC_XTAL=n
# OR
CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC=n
CONFIG_BOARD_ENABLE_DCDC=n

CONFIG_SERIAL=y
CONFIG_CONSOLE=y
CONFIG_UART_CONSOLE=y
CONFIG_UART_LINE_CTRL=n

These settings worked for me. Thank you for supporting.