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How to access U-Boot environment variables from Linux?
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/tools/env directory of the latest AMSDK.
Where is U-Boot environment 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.
What is Fw_printenv?
fw_printenv is a simple tool for printing the environment for the bootloader U-Boot. All environment variables matching the names given as arguments are shown. If fw_printenv is called without any arguments the entire environment is printed.
What is U-Boot env?
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 I check my U-Boot?
Try to read uboot version this way:
- Find uboot partition, eg. for MTD device: cat /proc/mtd.
- For /dev/mtd5: cat /dev/mtd5 | hexdump -C -n 64.
How do you delete an environment variable in U-Boot?
You can use the u-boot command “env default -a -f” to reset back to the default environment. Follow this by “saveenv” if you want the changes to be persistent. Another method is to erase the area where the environment is stored. This is often a partition in QSPI or a file on the SD card.
What is uImage in Linux?
uImage: an image file that has a U-Boot wrapper (installed by the mkimage utility) that includes the OS type and loader information. A very common practice (e.g. the typical Linux kernel Makefile) is to use a zImage file.
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. …
Is the U-Boot env file compatible with MTD?
But those tools are only usable on a MTD with UBIFS, and I’m running on a more “classical” file system (FAT for U-Boot, ext4 for Linux). I tried to find a format spec for U-Boot env file, unsuccessfully.
How can I set environment variables in U-Boot?
U-Boot makes use of environment variables which can be read and set from the U-Boot command line with printenv and setenv. It can be helpful to read and set these variables from Linux as well, for ex. to remote control some U-Boot processes like software updates.
How to make a read only MTD writable in Linux?
After inserting this module, I was successfully able to use flash_erase and nandwrite while booted in the kernel, whereas before, flash_erase was telling me: “error 13 (Permission denied)” Another option is to use the fw_setenv utility (built with u-boot) to modify u-boot’s saved environment variables from inside Linux.
Is there a way to make Uboot writable?
Another option is to use the fw_setenv utility (built with u-boot) to modify u-boot’s saved environment variables from inside Linux. That would require a reboot to run with the new bootargs, unlike loading a kernel module, but that’s much less work than using a serial cable.