Fastboot is a protocol that can be used to re-flash partitions on your device (update the flash file system in your devices). It is this small tool that comes with the Android SDK (Software Developer Kit), which is an alternative to the Recovery Mode for doing installations and updates. It first comes with Android. Google have submit the fastboot code to mainline U-boot. So we can use this protocol to flash partition on your device. There are three way to enter fastboot mode

Enter Fastboot mode

Fastboot key

Three steps to enter fastboot mode with fastboot key. Please refer to here for the fastboot key on Kylin board.

  1. Long press fastboot key without release
  2. Short press reboot key and release reboot key. This step trig SoC reboot.
  3. Count 3 second, make sure boot into U-boot and detected fastboot key. Then release fastboot key.

U-boot console

Enter U-boot console first. Use "fastboot 0" command to enter fastboot mode.

=> fastboot 0

Kernel console

Enter kernel console first. Use "reboot fastboot" command to enter fastboot.

rockchip@localhost:~$ reboot bootloader

You can use "lsusb" command to check if you are really in fastboot mode. You will find a USB device with VID 0x2207 in your computer.

$ lsusb
Bus 002 Device 063: ID 2207:0006

You can also use fastboot command to list devices

$ sudo fastboot -i 0x2207 devices
0123456789AB fastboot

Fastboot command

Rockchip use 0x2207 as its USB vendor ID. This VID is not in Google's original fastboot code. So every fastboot command have to use "-i" parameter to specify vid to fastboot.
To list all the Rockchip devices attached to your USB port in fastboot mode.

$ sudo fastboot -i 0x2207 devices
0123456789AB fastboot

To flash loader

$ sudo fastboot -i 0x2207 flash loader "path to your loader"

To flash Android boot image

$ sudo fastboot -i 0x2207 flash boot_a "path to your boot image"
0123456789AB fastboot

To flash Android system image

$ sudo fastboot -i 0x2207 flash system_a "path to your system image"
0123456789AB fastboot