Boot is interrupted when serial cable not connected

If we power on the ClearFog and do not have the console USB cable plugged in, the ClearFog will never finish booting. Waiting a few minutes and then plugging in the console USB cable and connecting from another PC, the => prompt (as described here https://solidrun.atlassian.net/wiki/spaces/developer/pages/197494345/LX2160A+Software#Booting-the-micro-SD-and-flashing-to-either-eMMC%2C-NVME-M.2-or-SATA-drive) is displayed. It is almost as if the “Hit any key to stop autoboot” detected a key press, even though nothing was plugged into the ClearFog.

On the other hand, if the ClearFog is powered on when the console USB cable is plugged in, the ClearFog will boot as normal. It is possible to interrupt the boot if desired, and if left alone it will autoboot.

How can we autoboot the ClearFog even if a cable is not plugged in? It is almost as if when the cable is not plugged in, electrical noise causes phantom key presses to interrupt the ClearFog’s boot.

This is not an issue I have heard about before. Perhaps your SOM is not fully seated and you are getting noise on the UART lines to the SOC? You can try re-seating the SOM to see if it is a mechanical issue. If you just want to overcome the issue in software, then you can configure u-boot to require a specific keypress to break the boot sequence rather than any key. This should also work around the issue you are seeing.

A software fix will do for now. How can I configure u-boot?

You can use the config option AUTOBOOT_KEYED

Thanks, is there a guide to build and flash a modified version u-boot to a ClearFog CX LX2 (or similar board)?

You can use our lx2160a_build repository. GitHub - SolidRun/lx2160a_build: Scripts to build basic images for LX2160A COM express type 7 modules You will need to add your custom config as a new patch under the patches/uboot-$(sdk versions) you are using.

Thanks for your help. I’ll give it a go once I have some time. As a workaround I’ve plugged a cable from the ClearFog’s console port into a spare USB port on the ClearFog, but won’t be able to depend on it forever.