Loading a Device Tree Overlay (dtbo file)

I have a BBB. I am using Buildroot to create a custom build. My kernel is 6.1.80.
I have a dtbo file that I placed in /lib/firmware.
My uEnv.txt file for u-boot is as follows:
set_mmc1=if test $board_name = A33515BB; then setenv bootpartition mmcblk1p2; fi
set_bootargs=setenv bootargs console=${console} root=/dev/${bootpartition} rw rootfstype=ext4 rootwait
uenvcmd=run set_mmc1; run set_bootargs;run loadimage;run loadfdt;printenv bootargs;bootz ${loadaddr} - ${fdtaddr}

The overlay does not appear to loaded by u-boot. I ran lsmod, and the overlay is not listed. If I run:
dmseg | grep ADAU
I get no return.
Any ideas on what I can try?

at beginning of boot, does it say retrieving uEnv.txt or extlinux.conf the dtbo need to go in the one that is being retrieved.

1 Like
Scanning mmc 0:1...
Found /extlinux/extlinux.conf
Retrieving file: /extlinux/extlinux.conf
135 bytes read in 4 ms (32.2 KiB/s)
1:	beaglebone-buildroot
Retrieving file: /zImage
11031040 bytes read in 691 ms (15.2 MiB/s)
append: console=ttyS0,115200n8 root=/dev/mmcblk0p2 rw rootfstype=ext4 rootwait
Retrieving file: /am335x-boneblack.dtb
99078 bytes read in 8 ms (11.8 MiB/s)
## Flattened Device Tree blob at 88000000
   Booting using the fdt blob at 0x88000000
   Loading Device Tree to 8ffe4000, end 8ffff305 ... OK

That is interesting. It does appear to retrieve extlinux.conf instead of uEnv.txt. I thought uEnv.txt was linked to uboot. I did notice the extlinux.conf file, but didn’t know what it was for. It does appear to load the BBB device tree, so I will see if I can get it to load my overlay. Am I in control of which file is used (extlinux.conf or uEnv.txt)? Should they contain the same information? If there is a doc you can point me to, that would be great!

no docs that i know of, about a year or two ago they changed from uEnv.txt to extlinux.conf. both were read by u-boot. as for which is used, older u-boots will still use uEnv.txt where newer ones will use extlinux.conf. don’t think you have any control which is used, uEnv.txt is just scripting that extends u-boot script, so if you have special needs for this script, you will just need to patch the script in u-boot.