Yocto Customizing U-Boot AM62

- 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= bitbake -c unpack virtual/bootloader
$ mkdir -p ../local_repos/
$ cp -a arago-tmp-default-glibc/work/-oe-linux/u-boot-variscite/<uboot version>/git/. ../local_repos/
$ cd ../local_repos/
$ 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= bitbake -c unpack virtual/bootloader
$ mkdir -p ../local_repos/
$ cp -a arago-tmp-default-glibc/work/-oe-linux/u-boot-variscite/<uboot version>/git/. ../local_repos/
$ cd ../local_repos/
$ 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 /local_repos/
$ vim board/variscite//.c
$ vim include/configs/.h
edit and save

$ git commit -a -m "my__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 /sources/meta-variscite-imx/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/;protocol=file"
SRCBRANCH_ = "" (or your own created branch)
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 " 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//tree/

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 /sources/meta-variscite-imx/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>/.git;protocol=git"
SRCBRANCH = "" (or your own created branch)
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 " 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.