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Stop Autoboot with a Keyboard Key

By default, the Omega2’s bootloader (U-Boot 2025.04-…) launches Linux automatically a fraction of a second after power-on. This can be interrupted with the reset button (GPIO38) to start the bootloader command line. However, GPIO38 is not always accessible on custom designs.

Changing two U-Boot environment variables lets you press a key on the serial console to stop the countdown and drop to the bootloader prompt, giving you time to flash firmware, tweak settings, or recover a bricked device.

Gather the requirements:​

  • Omega2 module running the new U-Boot v2025.04 bootloader (or newer) with access to:
    • serial command line on UART0 with USB-to-Serial chip
    • reset button (GPIO38)
    • Note: Access to all of the above is provided on the Omega2 Eval Boards
  • Host computer
  • USB cable to connect to the Omega

Step 1: Activate the Bootloader Command Line​

Connect to the Omega2 command line through serial. Then power on the device and press the SW Reset button at the same time.

info

The Reset button on the Omega2 Eval Boards and Omega2 Docks is connected to the active-high FW_RST/GPIO38 pin. Pressing the reset button sends a digital-high signal to the FW_RST/GPIO38 pin.

Autoboot will be disabled and the bootloader command line will be visible in the serial command line output.

You should now see the bootloader prompt:

U-Boot 2025.04-...
=>

Step 2: Set a Boot Delay​

Tell U-Boot how long to wait before starting Linux.

The command below sets a 2-second grace period.

env set bootdelay 2

Any value greater than 0 works.
A longer delay gives you more time to type but slows every boot.

Step 3: Choose a Stop-Boot Key​

Select the character (or short string) that will cancel autoboot during the delay.

env set bootstopkey 1

With the example above, pressing 1 during the 2-second countdown halts the boot process.
You can use any printable character (a–z, 0–9, etc.) or a short word such as debug.

Step 4: Save the Environment​

danger

saveenv writes the environment to flash. Incorrect values can make your device unbootable. Double-check the commands before saving.

saveenv

Settings persist across reboots once saved.

Step 5: Reboot and Test​

Reboot the Omega from the bootloader:

reset

As soon as the countdown banner appears, tap 1 a few times.
Successful output looks like this:

Hit any key to stop autoboot:  1
=>
tip

bootdelay 1 gives the fastest usable workflow—short wait, still easy to hit the key.

Additional Notes & Troubleshooting​

  • Reset button still works – holding it forces the bootloader prompt but only after the full bootdelay elapses.
  • Disable the feature by setting bootdelay 0 and saving: 
    env set bootdelay 0
    saveenv
  • Restore factory defaults if things go wrong: 
    env default -a
    saveenv

What’s Next?​