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This is kind like a U-Boot related question. I'm not quite sure which site should I post to, but as I boot Ubuntu, I post it here.

Basicly, I bought a cheap Nanopi Neo Air with Allwinner H3 SOC. I'm using the official ubuntu 20.04 image. I flashed the system into the onboard emmc with the eflasher tool provided.

The onboard emmc is too small for my use case, but it is faster than a sd-card. I want my system boot from emmc, while using sd-card as extra storage. So I formated my sd-card as one big ext4 partition, and rebooted my system.

When booting, my u-boot is not happy with a sd-card plugged in. It will always boot from the sd-card, even when it is empty (so it won't boot at all).

What did I try
I tried to purge all data in my sd-card by writing zeros into it. That did'nt help.

What do I want
Boot from emmc with sd-card plugged in

Any information appreciated.

1 Answer 1

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This is surely possible, but can't be answered generally, because the boot order and testing is individually defined in your U-Boot environment. For example, there can be some variable like bootdevs containing a list like mmc emmc saying to first try to boot from mmc, and if that fails, from emmc. In your case, I suspect there is a bad test implemented for mmc boot. Maybe it just checks whether the sdcard is there at all. This test must get extended to first test for a card to be present, then test for an ext4 filesystem, finally look for a file /boot/vmlinuz or whatever is the path of the kernel image.

If you don't have an explanation of your U-Boot configuration, it is no rocket science to reverse-engineer it. Do printenv boot in your U-Boot prompt and see what it does. It will probably run other commands, which you can also printenv. Maybe some command will not exist, because it get's generated during execution, so see the whole printenv output to see where and how it gets generated. The syntax is quite easy to learn.

If you can't manage it by yourself, post your printenv output here, so we can help you to debug and expand it.

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