nRF54L20 USB MSC Enumeration Failure – Continuous Bus Reset and Device Suspended Events

[Uma Maheshwar Reddy]

Hi Team,

USB detection is working correctly on the nRF54L20 controller. However, the USB MSC (Mass Storage Class) implementation is not functioning as expected. The device continuously reports Bus Reset and Device Suspended events, resulting in USB storage enumeration failure.

For your reference, I have attached the UART logs. Kindly review and help identify the root cause of the issue.

Regards,
Uma Maheshwar

Below are the UART logs for your reference  :

03-11-2026 18:01:56.718 [RX] - *** Booting nRF Connect SDK v3.4.1-b20f8619ba9a ***<CR><LF>
*** Using Zephyr OS v4.4.2-33fa6a7aac6a ***<CR><LF>
Starting USB Mass Storage Application<CR><LF>
VBUS detection supported - waiting for USB<CR><LF>
Ready - connect USB-C cable<CR><LF>
[00:00:00.025,482] <ESC>[0m<inf> udc_dwc2: Skip pinctrl configuration<ESC>[0m<CR><LF>

03-11-2026 18:02:08.232 [RX] - USBD message: VBUS ready<CR><LF>
USB Connected<CR><LF>

03-11-2026 18:02:08.423 [RX] - Filesystem mounted at /GND_DISK:<CR><LF>
USBD message: Device suspended<CR><LF>
USBD message: Bus reset<CR><LF>
USBD message: Device suspended<CR><LF>

03-11-2026 18:02:09.262 [RX] - [00:00:11.556,848] <ESC>[1;33m<wrn> udc_dwc2: Experimental DMA enabled<ESC>[0m<CR><LF>
[00:00:11.556,858] <ESC>[0m<inf> udc_dwc2: Hibernation enabled<ESC>[0m<CR><LF>
[00:00:11.556,949] <ESC>[0m<inf> flashdisk: Initialize device GND_DISK<ESC>[0m<CR><LF>
[00:00:11.556,957] <ESC>[0m<inf> flashdisk: offset ad000, sector size 512, page size 512, volume size 131072<ESC>[0m<CR><LF>
[00:00:11.683,937] <ESC>[1;33m<wrn> udc: Spurious suspend event<ESC>[0m<CR><LF>
[00:00:11.720,738] <ESC>[0m<inf> udc_dwc2: Prepare RX 0x00 doeptsiz 0x60080040<ESC>[0m<CR><LF>

03-11-2026 18:02:11.868 [RX] - USBD message: Device resumed<CR><LF>
USBD message: Bus reset<CR><LF>
USBD message: Device suspended<CR><LF>

03-11-2026 18:02:15.369 [RX] - USBD message: Device resumed<CR><LF>
USBD message: Bus reset<CR><LF>
USBD message: Device suspended<CR><LF>

03-11-2026 18:02:18.869 [RX] - USBD message: Device resumed<CR><LF>
USBD message: Bus reset<CR><LF>
USBD message: Device suspended<CR><LF>

03-11-2026 18:02:21.127 [RX] - USBD message: VBUS removed<CR><LF>
USB Disconnected<CR><LF>
Filesystem unmounted<CR><LF>

[Vidar Berg]

Hello,

If you have not already, please try to build the mass storage sample included in the nrf repo  (<sdk_root>/nrf/samples/zephyr/subsys/usb/mass/) with the following build command:

west build -b nrf54lm20dk/nrf54lm20b/cpuapp -p -- -DEXTRA_DTC_OVERLAY_FILE="ramdisk.overlay".

I did that here and did not manage to reproduce the issue on a nRF54LM20 DK. Are you testing on a custom board?

Best regards,

Vidar