[U-Boot] What shall u-boot do before passing 'root=/dev/ram0' to kernel?

Hi All,

Do you know that what u-boot shall do after passing 'root=/dev/ram0' to kernel? How kernel locates /dev/ram0? I want to use one ramdisk as my rootfs, but the kernel failed to mount the ramdisk, I set the u-boot parameter as below. setenv bootargs console=ttyS0,115200 root=/dev/ram0 ro mem=128M

kernel reports errors: No filesystem could mount root, tried: ext2 cramfs squashfs romfs Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(1,0)

root=/dev/ram1 also failed... What's the difference between /dev/ram0 and /dev/ram1?

And are there any requirement for the ramdisk image? Such as little/big endian, block size?

Thanks, Mike