Build Device Tree from Scratch (JetPack 4.6 on NRU-50)

A. Prepare Device Tree Building Environment

The device tree is similar to the BIOS of the x86 computer. The device tree describes the hardware components of a carrier board, which is commonly used for ARM-based Linux computers.

In a nutshell, you will build the device tree on your host machine, an x86 computer with Ubuntu, NVIDIA SDKManager, x86 to aarch64 cross-compiler installed. You can download the device tree source (.dtsi) from NVIDIA, modify, compile it, then flash the compiled result to NRU.

1. Download NVIDIA SDKManager

https://developer.nvidia.com/nvidia-sdk-manager

2. Install JetPack 4.6 for Xavier NX NVIDIA SDKManager

After installation, you will see a L4T folder.

# The default L4T folder path for JetPack 4.6 of Xavier NX is 
$HOME/nvidia/nvidia_sdk/JetPack_4.6_Linux_JETSON_XAVIER_NX_TARGETS/Linux_for_Tegra

3. Download Device Tree and Kernel Source from NVIDIA

export L4T=$HOME/nvidia/nvidia_sdk/JetPack_4.6_Linux_JETSON_XAVIER_NX_TARGETS/Linux_for_Tegra

cd $L4T

# "tegra-l4t-r32.6.1" menas JetPack 4.6, more JetPack and L4T mapping can be found on <https://developer.nvidia.com/embedded/jetpack-archive>
./source_sync.sh -k tegra-l4t-r32.6.1

Then you will find sources under L4T . The sourecs folder includes the kernel and device tree source code from NVIDIA.

root@nvidia-POC-500:~/nvidia/nvidia_sdk/JetPack_4.6_Linux_JETSON_XAVIER_NX_TARGETS/Linux_for_Tegra/sources# ll
total 16
drwxr-xr-x  4 root   root   4096 十一  5 10:46 ./
drwxrwxr-x 11 nvidia nvidia 4096 十一  5 10:40 ../
drwxr-xr-x  3 root   root   4096 十一  5 10:46 hardware/
drwxr-xr-x  5 root   root   4096 十一  5 10:46 kernel/

4. Download Toolchain to Compile aarch64 on x86 Computers

cd $HOME
mkdir $HOME/l4t-gcc
cd $HOME/l4t-gcc

wget http://releases.linaro.org/components/toolchain/binaries/7.3-2018.05/aarch64-linux-gnu/gcc-linaro-7.3.1-2018.05-x86_64_aarch64-linux-gnu.tar.xz

tar xf gcc-linaro-7.3.1-2018.05-x86_64_aarch64-linux-gnu.tar.xz

5. Create a Default Makefile Config

sudo -s

L4T=$HOME/nvidia/nvidia_sdk/JetPack_4.6_Linux_JETSON_XAVIER_NX_TARGETS/Linux_for_Tegra
TOOLCHAIN_PREFIX=$HOME/l4t-gcc/gcc-linaro-7.3.1-2018.05-x86_64_aarch64-linux-gnu/bin/aarch64-linux-gnu-
TEGRA_KERNEL_OUT=$L4T/build
KERNEL_MODULES_OUT=$L4T/sources/modules

cd $L4T

sudo make -C sources/kernel/kernel-4.9/ ARCH=arm64 O=$TEGRA_KERNEL_OUT tegra_defconfig

## Make kernel
### 1. change config if necessary
# vim $TEGRA_KERNEL_OUT/.config
### 2. make kernel
# make ARCH=arm64 O=$TEGRA_KERNEL_OUT LOCALVERSION=-tegra CROSS_COMPILE=${TOOLCHAIN_PREFIX} -j$(nproc)
### 3. the made kernel is under $TEGRA_KERNEL_OUT/arch/arm64/boot/Image

B. Create NRU-50 Device Tree from NX Dev Kit

Download NRU-50 related source code from NRU FTP.

The tar.gz includes nru50.conf and related source to compile nru50.dtb

C. Compile Device Tree

L4T=$HOME/nvidia/nvidia_sdk/JetPack_4.6_Linux_JETSON_XAVIER_NX_TARGETS/Linux_for_Tegra
TOOLCHAIN_PREFIX=$HOME/l4t-gcc/gcc-linaro-7.3.1-2018.05-x86_64_aarch64-linux-gnu/bin/aarch64-linux-gnu-
TEGRA_KERNEL_OUT=$L4T/build
KERNEL_MODULES_OUT=$L4T/build/modules
NRU50_dtb_name=nru50

cd $L4T

# in case of make clean
# make -C sources/kernel/kernel-4.9 clean

make -C sources/kernel/kernel-4.9/ ARCH=arm64 O=$TEGRA_KERNEL_OUT LOCALVERSION=-tegra CROSS_COMPILE=${TOOLCHAIN_PREFIX} -j$(nproc) dtbs

# Move the compiled device tree back to $L4T for easier flash
cp $TEGRA_KERNEL_OUT/arch/arm64/boot/dts/nru50.dtb .

## Decompile the compiled nru50.dtb for further verification
#sudo dtc -I dtb -O dts -o ${NRU50_dtb_name}_decompiled.dts $NRU50_dtb_name.dtb 2>/dev/null

D. Flash Device Tree

# Remeber to put NRU-50 in recovery mode and connect nru50 and Host Machine with micro USB cable.

L4T=$HOME/nvidia/nvidia_sdk/JetPack_4.6_Linux_JETSON_XAVIER_NX_TARGETS/Linux_for_Tegra
cd $L4T

# Flash all (Pinmux + Device Tree + System Image)
sudo ./flash.sh -r -d nru50.dtb nru50 mmcblk0p1

# Flash Device Tree Only
sudo ./flash.sh -r -k kernel-dtb -d nru50.dtb nru50 mmcblk0p1