Ok., thank you! I tried your workaround, but having still some problems here - In Petitboot it’s not possible to set up the boot order, after changing the first one (CoreElec - on eMMC) to the second place and the second to the first (here shown as NOLABEL, but it is Ubuntu) Petitboot shows only CoreElec…
After a restart there were both systems back again.
Restart from here, trying to boot CoreElec and yes, this works! Restart the system and now trying to boot NOLABEL, but now i’m sitting in front of a blank screen, nothing happens…
Normally, when only one card is inserted both systems starts without any problems, but my problem is that it’s not good to remove the eMMC for booting Ubuntu because I have built an optical S/PDIF-Port to the GPIO for my surround system and now it’s not so easy to open the case for every Linux booting, whitch I need only to have a good working webbrowser. If that would be inside CoreElec I’d have no problems at all.
Obvisiously there is still a major problem with the boot sequence, so I’m still wondering that Emuelec has no problems with this (switch to MMC, SD card in ->Emuelec, without SD ->CoreElec.
Today I’m giving up so far, maybe I will work more on it tomorrow. Any further solutions are welcome!
Many thanks for your help to this point!