Unlocking the ability to downgrade AML control boards to an earlier firmware version for subsequent installation of custom Vnish firmware

This manual describes the method for re-enabling this feature.

Before starting, ensure you have the following:

• AML control board and a 12V power supply.
• Computer or laptop with Windows installed
• Any USB-UART adapter with drivers installed (in our case, Silabs CP2102). A terminal program (in our case, Putty) for connecting and sending commands to the control board.

Perform the following steps:

1. Connect the adapter to the computer. Identify the assigned port number (in our case, COM7)

1. Identify the UART pins on the control board.

1. Connect the USB-UART adapter to the control board according to the scheme: GND - GND, RXD - LINUX_TX, TXD - LINUX_RX.

1. Open the Putty terminal window. Configure the port number and speed to 115200. Other parameters should remain at default.

1. At this stage, you can check the correctness of the connections. When power is supplied to the control board, the device's boot log will be displayed in the terminal window.

1. Disconnect power from the control board and short the JP2 jumper with tweezers or a screwdriver.

1. Ensure the terminal window is active. Apply power to the board. As soon as the first boot line appears in the terminal, quickly unshort the jumper and press the spacebar a couple of times in the active terminal window.

After these manipulations, the ENV should start loading.

If this does not happen, which is permissible, you need to perform the following actions.

Remove power from the control board, reapply it, and short jumpers JP1 or JP2 a couple of times. This will put the board into uboot boot mode.

As a result, the following messages should appear in the terminal window:

1. Enter the command setenv bitmain_usb_switch 1. This command enables the USB port.

1. Enter the command saveenv. This command saves the settings.

1. Reboot the control board. Now, the current version of the stock firmware can be downgraded, which will subsequently allow you to install Vnish.