Hi,
my ReSpeaker Core V2.0 is connected to an Arduino via 3v3 serial connection (TX/RX/GND). The Arduino cyclically sends sensor readings and accepts messages from the respeaker.
There are two problems in this setting:
- If respeaker reboots, uboot catches the data from arduino, interpretes it as a keystroke and enters boot menu (Press any key to interrupt boot…) where it is stuck forever
- Arduino gets disturbed by uBoot messages as well as kernel output
Can you please give some guidance how you built u-boot?
Did you have a board file at hand? Dito for other needed files, like devicetree.
Any Repo with the forked DENX code?
I only plan to boot from SD Card - no eMMC, so no bricking 
Any hints on the proper settings for disabling uboot menu - found a variable “silent” - so at least one half of Problem 2 is solved - already found kernel arguments passing serial port for logging and uboot setting for serial device addresses - any chances to set something there like /dev/null in linux?
Is this git a good starting point? https://github.com/rockchip-linux/u-boot
Thanks and best regards
Martin