In that log, do you see this line?
Hit any key to stop autoboot: 0
If you have minicom running, and see the “hit any key…”, then hitting a key on the keyboard would drop you into a U-Boot prompt. This is where you can examine the environment which chooses boot device and might indicate something related to the SD card.
To continue boot, simply type “boot” and the enter key.
To print all environment variables, run the command “printenv”.
I’m actually looking at a TX2, but it should be very similar (I’m removing my command line references to the particular TX2 board). If you examine “bootcmd”, then this will be something like (you can do things like “echo $bootcmd”):
bootcmd=run distro_bootcmd
Then you can drill down:
# echo $distro_bootcmd
for target in ${boot_targets}; do run bootcmd_${target}; done
Notice that “$boot_targets” will be a space delimited list of boot devices, and that this is iterating through that list (this is where the TX2 probably differs from your Nano, but it is all a variable and easily edited):
# echo $boot_targets
mmc1 mmc0 usb0 pxe dhcp
This loop tests devices mmc1 through dhcp by prefixing the name with “bootcmd_”, and then runs that through macro expansion. For example:
# echo $bootcmd_mmc1
setenv devnum 1; run mmc_boot
# echo $bootcmd_mmc1
setenv devnum 1; run mmc_boot
Now you might be interested in edit commands. Keep in mind that if you change a variable, but do not save, then the change applies only to the one boot, and then the edit will revert upon reboot. You can test things without worry until you run “saveenv”. See “help saveenv” and “help edit”. You can quote space delimited variables. Here I’ll make up a variable which won’t do anything:
# edit deleteme
edit: hello world
# echo $deleteme
hello world
…and if you reboot, then “deleteme” will be gone.
An edit you might be interested in testing:
# echo $boot_targets
mmc1 mmc0 usb0 pxe dhcp
# edit boot_targets
edit: mmc0
# echo $boot_targets
mmc0
If this works, then you can reboot, edit again, and “saveenv”.
See also:
https://devtalk.nvidia.com/default/topic/1056592/jetson-tx2/it-take-too-long-time-on-uboot-quot-retrieving-file-quot-/post/5358159/#5358159