Directly copy linux kernel and .dtb file to SD card's partition/directory?

Hi @danielt,

I confirm that the /lib/modules folder in rootfs of sd card was updated.

Yes, you are right. After booting up I can login (auto login, actually) as root from the console.

Thanks to being able to work in the console, now I’ve confirmed that this SD card does boot and the USB ethernet adapter does work. Now I can ssh to this DB410c successfully.
Thank you for your kind help: @danielt, @ndec, @Loic, @gubertoli!

Just found another issue: In the console, messages similar to the following lines appears periodically:

[ 1086.951376] remoteproc remoteproc1: remote processor 4080000.hexagon is now up
[ 1086.951679] remoteproc remoteproc1: handling crash #105 in 4080000.hexagon
[ 1086.958107] remoteproc remoteproc1: recovering 4080000.hexagon
[ 1086.966173] qcom-q6v5-pil 4080000.hexagon: fatal error received: fs_rmts_pm.c:853:[5, 7] rmts_read_iovec failed
[ 1086.970210] remoteproc remoteproc1: crash detected in 4080000.hexagon: type fatal error
[ 1088.766524] qcom-q6v5-pil 4080000.hexagon: watchdog received: fs_rmts_pm.c:853:[5, 7] rmts_read_iovec failed
[ 1088.766605] remoteproc remoteproc1: crash detected in 4080000.hexagon: type watchdog
[ 1092.062105] qcom-q6v5-pil 4080000.hexagon: failed receiving QMI response
[ 1097.182114] qcom-q6v5-pil 4080000.hexagon: timed out on wait
[ 1097.182289] remoteproc remoteproc1: stopped remote processor 4080000.hexagon
[ 1097.234088] qcom-q6v5-pil 4080000.hexagon: MBA booted, loading mpss

They are quite annoying as the text in the console become hard to read. Is there anything I can do to get rid of them?

To clarify this issue, I’ve repeated this experiments for few times. Fortunately, this symptom doesn’t appear any more. Now after I update the ‘boot’ partition in sd card with the boot-db410c.img build by myself, the sd card still boots and works normally.
Now I think its time to close this issue.
Many thanks to all the kind help from you!