billymore

@billymore I got this from AI. It's not perfect. I haven't done this before. 

To convert a standard Armbian root filesystem (typically an ext4 partition) into the rootfs.cpio.lzma.uboot format required for RAM booting, you must package the file tree into a CPIO archive, compress it with LZMA, and then wrap it with a U-Boot header.
 
1. Extract the Armbian RootFS 
First, you need the actual files from your Armbian image. Mount the image to a temporary directory on your Linux PC:
mkdir -p /tmp/armbian_root
 
If you have your Armbian .img file ready, run this command to find the start sector of the root partition (usually the second partition):
fdisk -l armbian_image.img
 
Multiply that Start number by 512 to get the exact offset for the mount command.
sudo mount -o loop,offset=YOUR_OFFSET armbian_image.img /tmp/armbian_root
 
A standard Armbian rootfs doesn't have an init file in the root directory; it uses sbin/init (a symlink to systemd). A RAM disk requires an executable at /init. 
sudo ln -s sbin/init /tmp/armbian_root/init
 
2. Create the CPIO Archive
Pack the entire filesystem into a newc format CPIO archive. It is critical to perform this step as root to preserve file permissions. 
cd /tmp/armbian_root
sudo find . | sudo cpio -H newc -o > /tmp/rootfs.cpio
 
3. Compress with LZMA 
Compress the archive using the LZMA algorithm to minimize its size for RAM loading:
lzma -9 /tmp/rootfs.cpio                # This creates /tmp/rootfs.cpio.lzma
 
4. Add the U-Boot Header 
Use the mkimage tool (from the u-boot-tools package) to add the 64-byte legacy header that U-Boot uses to identify the ramdisk. 
mkimage -A  arm64 -O linux -T ramdisk -C lzma -n "Armbian Initramfs" -d /tmp/rootfs.cpio.lzma /tmp/rootfs.cpio.lzma.uboot
 
-A arm: Target architecture (use arm64 if applicable).
-T ramdisk: Identifies the image type as a RAM filesystem.
-C lzma: Specifies the compression used.
-d: Input data file. 
 
sunxi-fel -v uboot u-boot-sunxi-with-spl.bin \ write 0x40080000 Image \ write 0x4fa00000 dtbs/allwinner/sun50i-h313-tanix-tx1.dtb \ write 0x4fe00000 rootfs.cpio.lzma.uboot (Note: If you are using a raw Image instead of a uImage, use booti instead of bootm).

 
Once U-Boot initializes over the USB cable, it will drop to a prompt. You must run this to start the OS:
Armbian’s default kernel might not have a large enough ramdisk_size allocated in its config.
Update your bootargs to include a size limit (in KB). If your rootfs is 500MB:
setenv bootargs "console=ttyS0,115200 root=/dev/ram0 rw" booti 0x40080000 0x4fe00000 0x4fa00000 ramdisk_size=600000  

@billymore The "Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)" error indicates that the Linux kernel could not locate or mount the root file system during startup. . 
 
 This is commonly caused by a missing or corrupted initial RAM filesystem (initramfs), an incorrect root= boot parameter
 
write 0x4ff00000 rootfs.cpio.lzma.uboot