A1: It means that your computer's attempt to communicate with your device's BootROM has failed. The BootROM's UART receive buffer is full, so it cannot hear the "GET" command your PC is sending to initiate recovery mode.
In short, Common Causes
The error message is a common and frustrating issue encountered when flashing, unbricking, or communicating with Set-Top Boxes (STBs). It most frequently occurs with devices running Amlogic, Rockchip, or Allwinner chipsets when using serial terminal tools like PuTTY, SecureCRT, or specialized flashing software. A1: It means that your computer's attempt to
: Try the most common baud rates in your software: 115200 , 57600 , or 9600 . or 9600 .