What is U-Boot environment variables?

Posted on by Emilia Duggan

What is U-Boot environment variables?

The U-Boot environment is a block of memory that is kept on persistent storage and copied to RAM when U-Boot starts. It is used to store environment variables which can be used to configure the system. The environment is protected by a CRC32 checksum.

How do you add environment variables in U-Boot?

The usual way to work with environment variables is to use the U-Boot shell to edit them.

  1. setenv – sets the value of an environment variable.
  2. saveenv – saves all environment variables.

How do you delete an environment variable in U-Boot?

If you are looking to delete a single existing u-boot env variable, from the u-boot command prompt, execute “setenv “. This should remove the variable name from the list of env variables.

How do you edit U-Boot?

How to Modify U-Boot Environment Variables in PetaLinux

  1. Store the environment variables in flash. When UBoot runs, it first tries to load its environment variables from the non-volatile storage (eg.
  2. Modify the hard-coded default values.
  3. Example: Let’s modify bootcmd.
  4. Rebuild, repackage and boot.

What is Bootargs in U-Boot?

When combined with a U-Boot variable named bootargs, this feature allows you to tell the kernel how to configure various device drivers, where to find the root filesystem and can even be used to pass information to applications on the system.

How do I set an environment variable in Linux at startup?

You can set your own variables at the command line per session, or make them permanent by placing them into the ~/. bashrc file, ~/. profile , or whichever startup file you use for your default shell. On the command line, enter your environment variable and its value as you did earlier when changing the PATH variable.

Where are U-Boot environment variables stored?

SD Card memory
The U-Boot environment is stored in the SD Card memory 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.

How does U-Boot pass Derb to kernel?

  1. The way bootloader works is that after doing some setup, it simply jumps onto Linux entry point.
  2. void TheKernel(char *cmdline, void* dtb);
  3. The kernel is passed the command line, and a pointer to the device tree binary, and then the function gets called, simple as that.