upgrade_tool is a firmware upgrade tool for Linux. Flash image requires superuser privileges.
1. Download and execute upgrade_tool first.
2. Put the firmware files and upgrade_tool in the same directory.
3. Connect the USB OTG port from the board to your PC, press the recovery button from your board, and connect the power, wait a few seconds and release the button.
4. Use the commands to flash image.
Basic Commands

  //List devices
  upgrade_tool ld   

  //Download boot
  upgrade_tool db rkxxloader.bin

  //Flash the partition table
  upgrade_tool di -p parameter.txt

  //Flash single partition image
  upgrade_tool di -k kernel.img

  //Falsh multiple partition images
  upgrade_tool di -u uboot.img -b boot.img

  //Flash the partition image with no defined abbreviation, you need to specify the partition name. 
  //Take the vendor partition as an example
  upgrade_tool di -vendor vendor.img

  //When ab partition are used, it also needs to be handled in undefined cases. 
  //Take boot_a and boot_b as example
  upgrade_tool di -boot_a boot.img -boot_b boot.img

  //Flash loader and reset
  upgrade_tool ul rkxxloader.bin  

  //Upgrade firmware and reset
  upgrade_tool uf update.img  

  //Erase device
  upgrade_tool ef rkxxloader.bin