6.2.5. Update U-Boot Environment Variables stored in SPI Flash from Linux¶
The purpose of this article is to demonstrate how the U-Boot Environment variables stored in SPI Flash can be accessed from a Linux command line using a tool provided from U-Boot.
- This example is based on the AMSDK, AM335x GP EVM and the User is has the latest version of the AMSDK installed
- Build(Cross Compile) fw_printenv/fw_setenv U-Boot Tool provided with U-Boot source in the AMSDK
- Prepare configuration file for U-Boot Tool fw_printenv/fw_setenv
- Load fw_printenv/fw_setenv into target file system
- Test fw_printenv/fw_setenv tool
To access the environment variables from Linux one of the tools from u-boot must be cross compiled and copied into the file system. This tool is located in the board-support/u-boot<version>/tools/env directory of the latest AMSDK.
Build(Cross Compile) fw_printenv/fw_setenv U-Boot Tool
Please note that all paths are refereneced to the u-boot source within the AMSDK, ti-sdk-am335x-<version>/board-support/u-boot<version>.....
Prior to building the The flag in board-support/u-boot<version>/tools/envfw_env.h “HAVE_REDUND” must be undefined as only a single env partition has been defined in the AMSDK SPI MTD partitioning.
Please note that the CROSS_COMPILE flag is not used by the u-boot makefile here, the HOSTCC= variable must be set.
host# make HOSTCC=arm-arago-linux-gnueabi-gcc env
This command is issued from the top of the u-boot source directory. Please be sure to see that the cross compiler was actually called and not just gcc.
Prepare configuration file for U-Boot Tool fw_printenv/fw_setenv
After building the executable a configuration file must be created and placed into a specific directory that is called in fw_env.h in the board-support/u-boot<version>/tools/env directory. The default location for the configuration file (fw_env.config) is /etc/.
/dev/mtd2 0x0000 0x2000 0x1000
Load fw_printenv/fw_setenv into target file system
This creates the executable fw_printenv, this file must be copied into the target file system, place in /sbin or the user’s directory.
You must copy fw_printenv to fw_setenv to be able to set variables. The program detects the name it was called as and sets the context it will run in.
Test fw_printenv/fw_setenv tool
The executable fw_printenv will dump the entire environment space, individual variables can be read by:
target# ./fw_printenv autoload
To set an environment variable use fw_setenv . This example will set the variable autoload to no, use fw_printenv to read back the change.
target# ./fw_setenv autoload no