Hello,
I’am getting more and more familiar with a VIM3/Pro.
After experimenting for quite awhile with SD’s I tried to write to eMMC using a Krescue image (VIMx.Debian.9.stretch.server.kernel-5.5.X.mainline.emmc.kresq) that is currently working very well. Now, I would like to go back to boot from an SD Coreelc image that I also worked with before flashing the eMMC but unfortunately, I am not anymore able to boot from SD again, just straight from the eMMC, even trying any of the several methods to enter upgrade mode. The only SD software that I am currently able to boot from is Krescue itself. I also noted that the usual Khadas logo is not any longer displayed when trying with no success to enter the upgrade mode.
I’ve read on the Khadas site that the upgrade mode can be activated only when an Android version 9 image is loaded into the eMMC. Does this fact has anything to do with my problem?
How can I revert back to a state so to either enter the upgrade mode or booting my Coreelec image on SD?
I really prefer asking before attempting more things, thank you for any hint
Bregards
Marco
Hi!
for my part, I can advise you to use the usb3.0 port to run CoreELEC as the second operating system, I have a high-speed flash drive from SanDisk usb-ssd and I am very pleased 
Well, in order to boot into sd, hold down the power button until the image loads.
yes, this fact also takes place
Running CoreELEC on a usb connected SSD as second operating system seems interesting to me but can you briefly hint at how the remaining usb would allow the mouse/keyboard pair connected? Is this a special setup or just a variant of the same boot mechanism?
As to Android v9 required to boot from SD as explained, however, what I am missing to understand, because I see it as a cumbersome way of booting… 
Thanks
usb hub via usb 2.0 port (preferably with additional food) 
as for the Android/coreelec pair, then everything is simple , there should be no problems ,but I see you have a different OS in priority ,here it will be difficult for me to confirm ,since I myself have not tried all the options