U-Boot

Das U-Boot (Universal Bootloader) is an open source, primary boot loader used in embedded devices. The version that is running on Eurotech hardware has been patched and adjusted to suit each platform. The patches for this platform can be found in the BSP source tree in the SDK. Refer to the Yocto Setup section for more information on how this is organised.

If you interrupted the normal boot process you will now see the U-Boot prompt which will look like this:
U-Boot>

At the prompt, you can type help to review the command options. Because of the configurable nature of U-Boot, the exact set of available commands on each system may vary.

U-Boot Environment Variables

Individual system configurations are typically done using environment variables. You can display all of the system variables with the printenv command

Board ID:

The system board id is stored in SPI flash. This needs to be set to boot the system with the correct machine type. Use


       setid 4962

to configure the system as a ReliaGATE 10-20 (solo) / CPU-351-13 (quad). You can also run setid without an ID value to see the current setting.

Boot Configuration:

The default environment is setup to boot from either SD or eMMC, depending on the boot configuration. Below are the default settings:


       mmc1root=/dev/mmcblk1p1
       mmc3root=/dev/mmcblk0p1

To see these values run


       printenv mmc1root
       printenv mmc3root

Bootting from SD-card on a system with no eMMC:

To boot from SD-card on a system with no eMMC, the environment must have


       mmc1root=/dev/mmcblk0p1

To make this change, save it, and boot with the new setting, run


     setenv mmc1root /dev/mmcblk0p1
     saveenv
     reset

Erasing the environment variables:

To erase your environment and use the default environment, use


       destroyenv

This is useful after reprogramming u-boot, especially if the default environment has changed. After saving or destroying the environment, it is best to reset the system or use the


       reset

command in u-boot to ensure your new environment is loaded cleanly.

NOTE: The u-boot environment is currently stored on the same media from which it boots. To change the eMMC u-boot environment, you must set the boot mode switches for eMMC, reset or cycle power, and boot from eMMC before making changes. Likewise, to change the environment on an SD card, you must set the boot mode switches for SD, reset or cycle power, and boot from SD first. The system does not check the boot configuration switches on reboot.