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Yocto Customize U-Boot

Introduction

This guide demonstrates how to patch and rebuild the VAR-SOM-AM62 U-Boot images using Yocto.

To learn how to build the U-Boot images outside of Yocto, see: Build U-Boot from source code

Before Starting

Before starting this guide, you must have the Yocto environment set and be able to build images for the VAR-SOM-AM62.

Please see: Build Yocto from source code.

The remainder of the guide assumes the Yocto working directory is ~/var-ti-yocto

Making changes in the source code

Choose one of the following three methods to customize the U-Boot source code and build it using Yocto:

Add your patches on top of the Variscite source code

Fetch the U-Boot source: 

MACHINE=am62x-var-som bitbake -c unpack virtual/bootloader
mkdir -p ../local_repos/ti-u-boot
cp -a arago-tmp-default-glibc/work/am62x_var_som-oe-linux/u-boot-variscite/<uboot version>/git/. ../local_repos/ti-u-boot
cd ../local_repos/ti-u-boot
git reset --hard
git clean -fdx
Next, make the desired changes to the U-Boot source code. After changing the source code, create a diff file: 
git diff > ~/var-ti-yocto/tisdk/sources/meta-variscite-bsp-ti/recipes-bsp/u-boot/u-boot-variscite/uboot.diff
Finally, configure ~/var-ti-yocto/tisdk/sources/meta-variscite-bsp-ti/recipes-bsp/u-boot/u-boot-variscite_<u-boot version>.bb to apply the patch by appending: 
SRC_URI += "file://uboot.diff"

Use a local repository

Fetch the U-Boot source: 

MACHINE=am62x-var-som bitbake -c unpack virtual/bootloader
mkdir -p ../local_repos/ti-u-boot
cp -a arago-tmp-default-glibc/work/am62x_var_som-oe-linux/u-boot-variscite/<uboot version>/git/. ../local_repos/ti-u-boot
cd ../local_repos/ti-u-boot
git reset --hard
git clean -fdx
Next, make the desired changes to the U-Boot source code. After making changes in the source code you need to commit them. For example: 
cd ~/var-ti-yocto/local_repos/ti-u-boot
vim board/variscite/am62x_var_som/am62x_var_som.c
vim include/configs/am62x_var_som.h
edit and save

git commit -a -m "my_am62x_var_som_changes"

To list all of the commits:
git log

Get the latest commit ID:
git rev-parse HEAD
Update the recipe to use the local repository instead of the default one: 
cd ~/var-ti-yocto/sources/meta-variscite-bsp-ti/recipes-bsp/u-boot/
Create a u-boot-variscite.bbappend file: 
vim u-boot-variscite_%.bbappend
Append the following lines to it (see the previous section for listing the commits or getting the latest commit ID): 
UBOOT_SRC = "git://<var-ti-yocto_directory_path>/local_repos/ti-u-boot;protocol=file"
SRCBRANCH:am62x-var-som = "ti-u-boot-2025.01_11.02.08.02_var01"
SRCREV:am62x-var-som = "The commit id you'd like to use"
For the SRCREV value you can also use "${AUTOREV}" during development to get the latest commit of the branch (If you do so, make sure to run "MACHINE=am62x-var-som bitbake -c cleansstate virtual/bootloader" before rebuilding U-Boot)

Use your remote repository on GitHub

Using this method Yocto will fetch the source code from your remote repository on GitHub.

Create a GitHub account and upload your proprietary U-Boot to a new repository: You can fork our repository to your account by visiting the following link and clicking on "Fork" at the top right of the screen: https://github.com/varigit/ti-u-boot/tree/ti-u-boot-2025.01_11.00.09.04_var01

Alternatively, you can clone the repository to your local machine, and push it later to your account.

Update the recipes to use your remote repository instead of the default one: 

cd ~/var-ti-yocto/sources/meta-variscite-bsp-ti/recipes-bsp/u-boot/
Create a u-boot-variscite.bbappend file: 
vim u-boot-variscite_%.bbappend
and append the following lines to it (see the previous section for listing the commits or getting the latest commit ID): 
UBOOT_SRC = "git://github.com/<your_account>/ti-u-boot.git;protocol=git"
SRCBRANCH = "ti-u-boot-2025.01_11.02.08.02_var01"
SRCREV = "The commit id you'd like to use"
For the SRCREV value you can also use "${AUTOREV}" during development to get the latest commit of the branch (If you do so, make sure to run "MACHINE=am62x-var-som bitbake -c cleansstate virtual/bootloader" before rebuilding U-Boot)

Building U-Boot using Yocto

After making the desired changes to the source code following one of the methods described in the Making changes in the source code, you can build the U-Boot images by running: 

cd ~/var-ti-yocto/tisdk/build
. conf/setenv

# Build only the U-Boot images:
MACHINE=am62x-var-som bitbake -c deploy u-boot-variscite                    # tispl.bin and u-boot.img
MACHINE=am62x-var-som bitbake -c deploy mc:k3r5:u-boot-variscite            # tiboot3.bin

# Optionally, you may skip building U-Boot and just build your image:
MACHINE=am62x-var-som bitbake <image name>
The relevant output files are: 
deploy-ti/images/am62x-var-som/u-boot.img
deploy-ti/images/am62x-var-som/tispl.bin
deploy-ti/images/am62x-var-som/tiboot3.bin
see: Build U-Boot from source code to learn how to update a running board with these images.