I have a ROC-RK3328-CC and a Libre-branded 128GB eMMC.
I successfully installed Libre’s ubuntu on the eMMC card and had it booting and running, but something went wrong and now it won’t boot. If I remove the eMMC and install a uSD card, it boots fine from the uSD card, but the question now is: how can I erase and re-flash the eMMC card?
By timing the hot-plug insertion of the eMMC just right, I was able to boot Armbian from the uSD card and also get it to recognize the eMMC card. The eMMC must be plugged in after boot from SD has started but before detection has started - in practice, it can be plugged in pretty quickly after power has been applied to the board. I have a piece of double-sided tape on the far end of the eMMC from the connector; this makes it a little easier to have the eMMC connector positioned correctly over the socket so it’s ready to just press in shortly after applying power.
After that, I was able to re-flash the bootloader and OS image and was able to boot from the eMMC again.
There has got to be a better way.