How to install u-boot and can anyone help what is the meaning of this text

OEM installation using the TFTP method

See also → generic.flashing.tftp

  1. Setup a TFTP server with address

  2. Copy the …initramfs-kernel.bin to TFTP server folder, rename as test.bin

  3. While starting U-boot press '4' key to stop autoboot

  4. From u-boot command prompt run tftpboot followed by bootm

Specific values needed for tftp

FIXME Enter values for “FILL-IN” below

Bootloader tftp server IPv4 address FILL-IN
Bootloader MAC address (special) FILL-IN
Firmware tftp image Latest OpenWrt release (NOTE: Name must contain “tftp”)
TFTP transfer window FILL-IN seconds
TFTP window start approximately FILL-IN seconds after power on
TFTP client required IP address FILL-IN

Which device are we talking about and what is the problem?

TFTP recovery methods are usually implemented in the bootloader, e.g. u-boot, if u-boot is damaged on your device it's game over for the 'easy' options (external flashing of the spi-nor or NAND needed, respectively in rare cases serial based recovery (e.g. lantiq, mvebu)).