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Using U-Boot Environment Print

 

U-Boot makes use of the so-called environment variables to define various aspects of the target functionality. On the STM32F4 SOM, the U-Boot environment is stored in the on-module NOR Flash and is persistent across power or reset cycles. Parameters defined by the U-boot environment variables include: target IP address, target MAC address, location in RAM where a Linux bootable image will be loaded, and many others.

To manipulate the U-Boot environment the following commands are used:

  • printenv <var> - print the value of the variable var. Without arguments, prints all environment variables:
  • STM32F4X9-SOM> printenv
    bootcmd=run flashboot
    bootdelay=3
    baudrate=115200
    hostname=stm32f4x9-som
    ...
    Environment size: 892/4092 bytes
    STM32F4X9-SOM>

  • setenv <var> <val> - set the variable var to the value val:
  • STM32F4X9-SOM> setenv image vlad/networking.uImage
    STM32F4X9-SOM>

    Running setenv <var> will unset (undefine) a specified U-Boot variable, so it won't be shown as available next time you run printenv.

  • saveenv - save the up-to-date U-Boot environment, possibly updated using setenv commands, into internal Flash. Running saveenv makes sure that any updates you have made to the U-Boot environment are persistent across power cycles and resets. If you don't run saveenv, any updates you may have made to the U-Boot environment will be lost on next reboot.
  • STM32F4X9-SOM> saveenv
    Saving Environment to Flash...
    . done
    Un-Protected 1 sectors
    Erasing Flash...
    . done
    Erased 1 sectors
    Writing to Flash... done
    . done
    Protected 1 sectors
    STM32F4X9-SOM>