1. Copy and paste the existing EVM A53 and R5 Kconfig targets in TI_U_BOOT/arch/arm/mach-k3/am62x/
Kconfig and rename the symbols for the custom board. Optionally, modify the corresponding board specific 
string. An example is below.

+ config TARGET_AM625_A53_<BOARDNAME>
+ bool "<COMPANY> K3 based AM625 <BOARDNAME> running on A53"
+ select ARM64
+ select BINMAN
+ select OF_SYSTEM_SETUP
+ config TARGET_AM625_R5_<BOARDNAME>
+ bool "<COMPANY> K3 based AM625 <BOARDNAME> running on R5"
+ select CPU_V7R
+ select SYS_THUMB_BUILD
+ select K3_LOAD_SYSFW
+ select RAM
+ select SPL_RAM
+ select K3_DDRSS
+ select BINMAN
+ imply SYS_K3_SPL_ATF

Add the following line to the bottom of the same Kconfig file.
+ source "board/<company>/<boardname>/Kconfig

2. Make new <company> and <boardname> directories to store files that will be copied and modified.
$ mkdir -p TI_U_BOOT/board/<company>/<boardname>/
$ mkdir -p TI_U_BOOT/board/<company>/common/

3. Copy and rename board files from the TI directory to the new directories.
$ cp TI_U_BOOT/board/ti/am62x/* TI_U_BOOT/board/<company>/<boardname>
$ cp TI_U_BOOT/board/ti/common/* TI_U_BOOT/board/<company>/common 

4. In the TI_U_BOOT/board/<company>/<boardname> directory, edit the Kconfig by modifying the default 
value of the configuration options as seen below.
if TARGET_AM625_A53_<BOARDNAME>
config SYS_BOARD
 default "<boardname>"
config SYS_VENDOR
 default "<company>"
config SYS_CONFIG_NAME
 default "<boardname>_evm"
source "board/<company>/common/Kconfig"
endif
if TARGET_AM625_R5_<BOARDNAME>
config SYS_BOARD
 default "<boardname>"
config SYS_VENDOR
 default "<company>"
config SYS_CONFIG_NAME
 default "<boardname>_evm"
config SPL_LDSCRIPT
 default "arch/arm/mach-omap2/u-boot-spl.lds"
source "board/<company>/common/Kconfig"
endif

4. In the same directory, rename the file evm.c to <boardname>.c and the file am62x.env to <boardname>.env.
In the same directory, edit the Makefile as seen below.
- obj-y += evm.o
+ obj-y += <boardname>.o

5. Copy the EVM board header file and rename the file for the custom board.
$ cp TI_U_BOOT/include/configs/am62x_evm.h TI_U_BOOT/include/configs/am62x_<boardname>.h
Make the following modification inside the newly created header file.
- #ifndef __CONFIG_AM625_EVM_H
- #define __CONFIG_AM625_EVM_H
+ #ifndef __CONFIG_AM625_<BOARDNAME>_H
+ #define __CONFIG_AM625_<BOARDNAME>_H

6. Create the following configuration fragments in TI_U_BOOT/configs/ and add the lines below to set the 
Kconfig targets.

am62x_<boardname>_r5.config

CONFIG_TARGET_AM625_R5_<BOARDNAME>=y
# CONFIG_TARGET_AM625_R5_EVM is not set

am62x_<boardname>_a53.config

CONFIG_TARGET_AM625_A53_<BOARDNAME>=y
# CONFIG_TARGET_AM625_A53_EVM is not set

7. Device tress were downloaded in the references section.

$ cp TI_U_BOOT/arch/arm/dts/k3-am625-minimal.dts TI_U_BOOT/arch/arm/dts/k3-am625-<boardname>.dts
$ cp TI_U_BOOT/arch/arm/dts/k3-am625-r5-minimal.dts TI_U_BOOT/arch/arm/dts/k3-am625-r5-
<boardname>.dts
$ cp TI_U_BOOT/arch/arm/dts/k3-am625-minimal-u-boot.dtsi TI_U_BOOT/arch/arm/dts/k3-am625-
<boardname>-u-boot.dtsi
These naming changes need to be reflected in the #include preprocessor directives in k3-am625-r5-
<boardname>.dts.

// in k3-am625-r5-<boardname>.dts
- #include "k3-am625-minimal.dts"
- #include "k3-am625-minimal-u-boot.dtsi"
+ #include "k3-am625-<boardname>.dts"
+ #include "k3-am625-<boardname>-u-boot.dtsi"

8. $ cp k3-am62x-ddr-config.dtsi TI_U_BOOT/arch/arm/dts/k3-am62x-<boardname>-ddr4-<#MTs>.dtsi
Replace the following line in k3-am625-r5-<boardname>.dts.
- #include "k3-am62x-sk-ddr4-1600MTs.dtsi"
+ #include "k3-am62x-<boardname>-ddr4-<#MTs>.dtsi"

9. Setup Binman for Custom Board.
Binman is used to generate U-Boot binaries. Use the following command to duplicate the existing EVM 
binman devicetree file and rename it for a custom board.

$ cp TI_U_BOOT/arch/arm/dts/k3-am625-sk-binman.dtsi TI_U_BOOT/arch/arm/dts/k3-am625-<boardname>-
binman.dtsi

In this newly created file, make the following modification to use the custom devicetree.
- #define SPL_AM625_SK_DTB "spl/dts/k3-am625-sk.dtb"
+ #define SPL_AM625_SK_DTB "spl/dts/k3-am625-<boardname>.dtb"

Include this new file in k3-am625-<boardname>-u-boot.dtsi.
- #include "k3-am625-sk-binman.dtsi"
+ #include "k3-am625-<boardname>-binman.dtsi"

10. dtb-$(CONFIG_SOC_K3_AM625) += k3-am625-sk.dtb \
 k3-am625-r5-sk.dtb \
 k3-am62sip-r5-sk.dtb \
 k3-am625-beagleplay.dtb \
 k3-am625-r5-beagleplay.dtb \
 k3-am625-verdin-wifi-dev.dtb \
 k3-am625-verdin-r5.dtb \
 k3-am625-phyboard-lyra-rdk.dtb \
 k3-am625-r5-phycore-som-2gb.dtb \
 k3-am62-lp-sk.dtb \
 k3-am62-r5-lp-sk.dtb \
+ k3-am625-<boardname>.dtb \
+ k3-am625-r5-<boardname>.dtb

11. 
am62x_<boardname>_r5.config
CONFIG_DEFAULT_DEVICE_TREE="k3-am625-r5-<boardname>"

am62x_<boardname>_a53.config
CONFIG_DEFAULT_DEVICE_TREE="k3-am625-<boardname>"
CONFIG_SPL_OF_LIST="k3-am625-<boardname>"
CONFIG_OF_LIST="k3-am625-<boardname>"

12. 
$ export CROSS_COMPILE_64="${SDK_INSTALL_DIR}/linux-devkit/sysroots/x86_64-arago-linux/usr/bin/aarch64-oe-linux/aarch64-oe-linux-"
$ export SYSROOT_64="${SDK_INSTALL_DIR}/linux-devkit/sysroots/aarch64-oe-linux"
$ export CC_64="${CROSS_COMPILE_64}gcc --sysroot=${SYSROOT_64}"
$ export CROSS_COMPILE_32="${SDK_INSTALL_DIR}/k3r5-devkit/sysroots/x86_64-arago-linux/usr/bin/arm-oe-eabi/arm-oe-eabi-"

$ export LNX_FW_PATH=TI_SDK/board-support/prebuilt-images/am62xx-evm/
$ export TFA_PATH=TI_SDK/board-support/prebuilt-images/am62xx-evm/bl31.bin
$ export OPTEE_PATH=TI_SDK/board-support/prebuilt-images/am62xx-evm/bl32.bin

$ export UBOOT_CFG_CORTEXR="am62x_evm_r5_defconfig am62x_<boardname>_r5.config"
$ export UBOOT_CFG_CORTEXA="am62x_evm_a53_defconfig am62x_<boardname>_a53.config"

13. 
$ make clean O=OUTPUT_DIR/r5
$ make ARCH=arm CROSS_COMPILE="$CROSS_COMPILE_32" $UBOOT_CFG_CORTEXR O=OUTPUT_DIR/r5
$ make ARCH=arm CROSS_COMPILE="$CROSS_COMPILE_32" O=OUTPUT_DIR/r5 BINMAN_INDIRS=$LNX_FW_PATH