Building fw printenv and fw setenv

Building fw printenv and fw setenv

Contents [hide] 1 Overview 2 Building the tools 3 Installing the executable(s) and config file 4 Creating the config file 5 Printing the U-Boot environment 6 Changing U-Boot environment variables with fw_setenv

[edit]Overview

You can access and change the U-Boot environment from Linux userspace using the "U-Boot tools" fw_printenv and fw_setenv, which you can build from the current U-Boot source
and install on the target system. You can see the source for those in the U-Boot source directory, under tools/env/.

[edit]Building
the tools

From the top of the U-Boot source code, you need to explicitly identify the GCC cross-compiler you want to use for the build, as in (for example):

$ make HOSTCC=arm-arago-linux-gnueabi-gcc env

This will create the cross-compiled executable tools/env/fw_printenv. Note that the Makefile will also try to strip that executable but the README file fails to mention that you'd
need to also identify the cross-compile version of the strip command, as in HOSTSTRIP=arm-arago-linux-gnueabi-strip. That's not a fatal problem since stripping the executable is optional, so that's up to you.

[edit]Installing
the executable(s) and config file

The resulting executable fw_printenv actually does double duty for both printing and setting U-Boot environment variables, so you need to install it in the root filesystem and create
an additional symlink to it on the target system. For example (assuming you're logged into the target):

# cd /usr/bin
# ... copy fw_printenv here
# ln -s fw_printenv fw_setenv

Now you can run that single executable by either name and it will do the right thing.

[edit]Creating
the config file

Finally, you need to create the U-Boot environment config file /etc/fw_env.config file on the target system which identifies the properties of the U-Boot environment flash partition.
A sample file is in the U-Boot tools/env source directory and it should be fairly self-explanatory. In my case, since the U-Boot environment was in the very first NAND flash partition and was 128K in size with a flash sector size also of 128K, my fw_env.config file
looked like:

# MTD device    Offset     Env size     Flash sector size

/dev/mtd0       0x0        0x20000      0x20000

[edit]Printing
the U-Boot environment

If all goes well, once you boot, you can list the U-Boot environment from Linux userspace:

# fw_printenv
DE:AD:BE:EF:01:02== ethaddr
baudrate=115200
bootargs=console=ttyS2,115200n8 root=/dev/mtdblock5 rootfstype=jffs2 ip=off
bootcmd=nand read C0700000 200000 300000; bootm C0700000
bootdelay=10
bootfile="uImage"
davinci_emac.ethaddr=DE:AD:BE:EF:01:02
ethact=DaVinci-EMAC
ethaddr=DE:AD:BE:EF:01:02
fileaddr=C0700000
filesize=21362C
ipaddr=192.168.3.12
serverip=192.168.3.2
stderr=serial
stdin=serial
stdout=serial
#

and use fw_setenv to change it as well.

[edit]Changing
U-Boot environment variables with fw_setenv

Pretty straightforward, but you need to make sure the U-Boot environment partition in flash isn't set as write-protected in your kernel partition table; otherwise, any attempt to change environment
information will give you a permission violation. You can still use fw_printenv to list it, of course.