usbd_cdc_acm examples bricks nrf52840 PDK

[Mike]

I've got a new nrf52840 PDK. I got Eclipse, JLink, and the nrf command line tools to work today. I've been able to run the precompiled examples (blinky, led_softblink), compile and run both of them, and step thru blinky using Eclipse a source line at a time. All good!

Then I tried the usbd_cdc_acm example by copying the copying the _pca10056.hex file to the JLink mount point. The eval board reset and then nothing! It no longer shows up as a MSD drive nor as a USB device at all! Power cycling and resetting the board does nothing.

If I hold down the IF BOOT/RESET button and then apply power, the board appears to go into "bootloader" mode. The IF LED is blinking, Windows thinks it's a MBED USB drive, there's an empty bootloader.htm file on it. But the bootloader quickly (30 seconds) gets some kind of error and Windows unmounts the drive, and complains about an unknown error.

I've seen in other postings on the DevZone that when it's in "bootloader" mode, I should drag and drop the offical Nordic firmware image for my board. Unfortunately, I can't find any such firmware image. I can find the nrf52832's MBED and JLink images, but I'm not brave enough (yet!) to try it on the nrf52840.

Any ideas on what I did wrong with the usbd_cdc_acm example? And more importantly, how I might rescue my board?

Thanks,

Mike

[Mike]

I have two of v0.9.2 boards and neither works for nRF USB. That includes the generic HID example.

In both examples, LED1 comes on briefly and then goes off about the time Windows 10 complains that the USB device failed on the Device Descriptor Request.

Looking at the schematics, the D_N,D_P pin pair on the nRF52840 looks like it's connected directly to the "nRF USB" port (J3). That would lead me to believe that it's a software problem. Or a board configuration problem.