Update README file for buildroot external tree

README.md

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-# buildroot-external-TI
+# TI Buildroot external tree
+
+Buildroot is a tool/build framework that simplifies and automates the process of
+building complete Linux systems for embedded devices. It simplifies the process
+of building a cross-compiled toolchain, a root filesystem, a Linux kernel,
+and a bootloader. This repository is a Buildroot `BR2_EXTERNAL` tree
+dedicated to supporting TI's SITARA platforms.
+
+The use of an external tree, such as buildroot-external-TI, allows for
+customization and extension of Buildroot without modifying the original
+Buildroot source. Upstream Buildroot also contains pre-defined
+configurations for SITARA platforms, but they use the upstream versions
+of U-Boot and Linux, while the configurations in this `BR2_EXTERNAL`
+tree uses the versions provided and supported by TI.
+
+## Available configurations
+
+This `BR2_EXTERNAL` tree provides two Buildroot configurations:
+
+1. `ti_release_am62x_sk_defconfig` for Linux
+2. `ti_release_am62x_sk_rt_defconfig` for RT-Linux.
+
+It supports following variants of AM62x EVM:
+- [SK-AM62](https://www.ti.com/tool/SK-AM62)
+- [SK-AM62B](https://www.ti.com/tool/SK-AM62B)
+- [SK-AM62B-P1](https://www.ti.com/tool/SK-AM62B-P1)
+
+It builds and packages following main components:
+- [ti-u-boot](https://git.ti.com/cgit/ti-u-boot/ti-u-boot/)
+- [ti-linux-kernel](https://git.ti.com/cgit/ti-linux-kernel/ti-linux-kernel/)
+- [optee](https://github.com/OP-TEE/optee_os)
+- [TF-A](https://github.com/ARM-software/arm-trusted-firmware)
+- [ti-linux-firmware](https://git.ti.com/cgit/processor-firmware/ti-linux-firmware)
+- [busybox](https://git.busybox.net/busybox/)
+
+## Pre-built SD card images
+
+Pre-built buildroot SD card images are available at:
+
+- [PROCESSOR-SDK-AM62X](https://www.ti.com/tool/PROCESSOR-SDK-AM62X)
+
+## Building Buildroot from source
+
+### Pre-requisites
+
+To use Buildroot, a Linux distribution must be installed on your workstation.
+Any reasonably recent Linux distribution (Ubuntu, Debian, Fedora, Redhat,
+OpenSuse, etc.) is suitable.
+
+Additionally, a small set of packages must be installed
+[Buildroot manual System requirements
+section](https://buildroot.org/downloads/manual/manual.html#requirement).
+
+For Debian/Ubuntu distributions, the necessary packages can be installed with
+the following command:
+
+```bash
+$ sudo apt install debianutils sed make binutils build-essential gcc g++ bash patch gzip bzip2 perl tar cpio unzip rsync file bc git findutils wget
+```
+
+Optional dependencies are available for enabling Buildroot features such as
+interface configuration, legal information and documentation. For detailed
+information refer
+[corresponding manual section](https://buildroot.org/downloads/manual/manual.html#requirement-optional).
+
+### Steps to build the SD card image
+
+- Clone the Buildroot repository to local machine.
+
+```bash
+$ git clone -b 2024.05.1 https://github.com/buildroot/buildroot
+```
+
+- Clone the `BR2_EXTERNAL` tree:
+
+```bash
+$ git clone -b 10.00.07 https://github.com/TexasInstruments/buildroot-external-TI.git
+```
+
+- The directories for `buildroot` and `buildroot-external-ti` are now located
+side-by-side.
+
+### Configure and build
+
+- Go to the Buildroot directory:
+
+```bash
+$ cd buildroot/
+```
+
+- Configure Buildroot to use the external tree by setting the BR2_EXTERNAL environment
+variable. This tells Buildroot to include the configurations and packages from
+the external tree during the build process. To configure the system for build,
+choose any of the *defconfigs*  provided in this `BR2_EXTERNAL` tree. For example:
+
+```bash
+For AM62X
+buildroot/ $ make BR2_EXTERNAL=../buildroot-external-TI ti_release_am62x_sk_defconfig
+```
+
+- To further customize the Buildroot configuration, run `make menuconfig`. This
+step is optional but useful if you need to make specific adjustments.
+
+- Build the SD card image for SDK 10.0
+
+```bash
+buildroot/ $ make TI_K3_BOOT_FIRMWARE_VERSION=10.00.07
+```
+
+- This process compiles the necessary components and creates the root filesystem,
+kernel, and bootloader. The build process can take some time, depending on your
+system's resources and the complexity of the configuration.
+
+## Flashing and booting the SD card image
+
+- The Buildroot configurations generate a compressed ready-to-use SD card image,
+available as `output/images/sdcard.img`.
+
+- Flash the image on a SD card:
+
+```bash
+buildroot/ $ sudo dd if=output/images/sdcard.img of=/dev/sdX
+```
+
+Replace /dev/sdX with the appropriate device identifier for your SD card.
+
+- Tools like [balena-ethcer](https://etcher.balena.io/) can also be used to flash
+the SD card image.
+
+- Insert the SD card in SD card slot and power on the board. The system will start,
+with the console on UART. You can log-in as `root` with no password.
+
+# Going further
+
+* [PROCESSOR-SDK-AM62X](https://www.ti.com/tool/PROCESSOR-SDK-AM62X#overview)
+
+# References
+
+* [Buildroot](https://buildroot.org/)
+* [Buildroot reference manual](https://buildroot.org/downloads/manual/manual.html)
+* [Buildroot system development training course](https://bootlin.com/training/buildroot/)
+
+# Technical support
+
+Visit [E2E](https://e2e.ti.com/support/processors/) for Technical support.