==NVIDIA SDK Manager==
You can get NVIDIA SDK Manager from URL below (need a development account):

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

For the version of kernel source, JetPack 4.4.1 is needed.

==Build Kernel==
Extract kernel source package, then:
<pre>
source env.sh
./nvbuild.sh
</pre>

==Deploy Kernel==
Copy the files below to the running system of Jetson Xavier NX board:
<pre>
deploy/Image
deploy/tegra194-p3668-all-p3509-0000.dtb
deploy/modules.tar.gz
</pre>

On the system of the board:
<pre>
cp Image /boot/
cp tegra194-p3668-all-p3509-0000.dtb /boot/
cp tegra194-p3668-all-p3509-0000.dtb /boot/dtb/kernel_tegra194-p3668-all-p3509-0000.dtb
cp modules.tar.gz /boot/
tar -xf modules.tar.gz -C /
</pre>

Run 40-pin IO configuration tool:
<pre>
sudo /opt/nvidia/jetson-io/jetson-io.py
</pre>

Configure 40-pin expansion header -> Select aud_mclk, i2s5 -> Back -> Save and reboot to reconfigure pins.

If aud_mclk and i2s5 is already selected, toggle any unused pinmux like pwm1 to force the tool re-create device tree files.

==Configure ALSA Mixer==
Only need to run the commands below once:
<pre>
sudo -s

amixer -c jetsonxaviernxa sset 'ADMAIF1 Mux' 'I2S5'
amixer -c jetsonxaviernxa sset 'I2S5 Mux' 'ADMAIF1'

amixer -c jetsonxaviernxa cset name="x HP Playback Switch" on
amixer -c jetsonxaviernxa cset name="x HPO MIX DAC1 Switch" on
amixer -c jetsonxaviernxa cset name="x Stereo DAC MIXL DAC L1 Switch" on
amixer -c jetsonxaviernxa cset name="x Stereo DAC MIXR DAC R1 Switch" on
amixer -c jetsonxaviernxa cset name="x DAC MIXL INF1 Switch" on
amixer -c jetsonxaviernxa cset name="x DAC MIXR INF1 Switch" on
amixer -c jetsonxaviernxa cset name="x DAC MIXL Stereo ADC Switch" off
amixer -c jetsonxaviernxa cset name="x DAC MIXR Stereo ADC Switch" off

amixer -c jetsonxaviernxa cset name="x ADC Capture Switch" on
amixer -c jetsonxaviernxa cset name="x Stereo1 ADC MIXL ADC1 Switch" on
amixer -c jetsonxaviernxa cset name="x Stereo1 ADC MIXR ADC1 Switch" on

amixer -c jetsonxaviernxa sset 'I2S5 BCLK Ratio' 256
amixer -c jetsonxaviernxa sset 'I2S5 Channels' 2
amixer -c jetsonxaviernxa sset 'I2S5 Sample Rate' 44100
amixer -c jetsonxaviernxa sset 'I2S5 codec bit format' 16
amixer -c jetsonxaviernxa sset 'I2S5 codec frame mode' 'dsp-a'
amixer -c jetsonxaviernxa sset 'I2S5 input bit format' 16
amixer -c jetsonxaviernxa sset 'ADMAIF1 Channels' 2

amixer -c jetsonxaviernxa cset name="x RECMIXL INL1 Switch" on
amixer -c jetsonxaviernxa cset name="x RECMIXR INR1 Switch" on
amixer -c jetsonxaviernxa cset name="x RECMIXL BST1 Switch" on
amixer -c jetsonxaviernxa cset name="x RECMIXR BST1 Switch" on

alsactl store
</pre>

==Dump eMMC==
Need JetPack package from NVIDIA Jetson SDK.
Set board to recovery mode, use commands below on PC (use JetPack 4.5.1 as example):
<pre>
cd JetPack_4.5.1_Linux_JETSON_XAVIER_NX/Linux_for_Tegra
sudo ./flash.sh -r -k APP -G system2.img jetson-xavier-nx-devkit-emmc mmcblk0p1
sudo mv -v system2.img bootloader/system.img
sudo mv -v system2.img.raw bootloader/system.img.raw
</pre>

==Restore eMMC==
Need JetPack package from NVIDIA Jetson SDK.
Set board to recovery mode, use commands below on PC (use JetPack 4.5.1 as example):
<pre>
cd JetPack_4.5.1_Linux_JETSON_XAVIER_NX/Linux_for_Tegra
sudo ./flash.sh -r jetson-xavier-nx-devkit-emmc mmcblk0p1
</pre>

==Overlay rootfs==
Warning: The operations below may break your OS on eMMC, backup your eMMC first!

Edit /etc/initramfs-tools/initramfs.conf as root, check MODULES=most section, and change it to MODULES=dep. Then run command:
<pre>
sudo update-initramfs -u
</pre>

Install overlayroot:
<pre>
sudo apt-get install overlayroot
</pre>

Edit /boot/extlinux/extlinux.conf as root, check ''INITRD /boot/initrd'', and change it to ''INITRD /boot/initrd.img-4.9.201-tegra''.

Edit /etc/overlayroot.conf as root, check ''overlayroot=""'', change it to line below (add one if no such pattern exists):
<pre>
overlayroot="tmpfs:swap=1,recurse=0"
</pre>

Reboot to apply changes.

If you want to go into writable rootfs temporary, you can use command below:
<pre>
sudo overlayroot-chroot
</pre>

If you want to remove overlayroot, just go into writable rootfs with ''overlayroot-chroot'', and edit /etc/overlayroot.conf, set variable overlayroot to overlayroot="" then reboot.