View source for Accessing U-Boot environment variables from Linux

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.  The U-Boot distribution has sources for these commands, named ''fw_printenv'' and ''fw_setenv''.

== Installation ==

{{Note|U-Boot tools are now installed and configured on your APF since Armadeus 5.0. Therefore following installation procedure is only useful for reference information.}}

Buildroot can automatically build these tools for you. You just have to:
<pre class="host">
$ make menuconfig
</pre>
and then select the following option:
<pre class="config">
 Hardware handling  --->
     [*] u-boot tools
         [*]   fw_printenv
</pre>

Tools will be installed in ''/usr/sbin/'' of your target's rootfs.

Then you have to create the config file for the utilities. The file name is ''fw_env.config'' and it lives in ''/etc''.
To create this file, you need to know informations about where U-Boot stores its env variables.  Specifically, you need the mtd device name, the device offset, the env size and the flash sector size. You can guess most of them by looking at ''/proc/mtd''.

* For the [[APF27]] with U-Boot 1.3.4:
<pre class="apf">
# Configuration file for fw_(printenv/saveenv) utility.
# Up to two entries are valid, in this case the redundand
# environment sector is assumed present.
# Notice, that the "Number of sectors" is ignored on NOR.
# MTD device name       Device offset   Env. size       Flash sector size       Number of sectors
/dev/mtd1                 0x0000          0x20000           0x20000                 3
</pre>

* For the [[APF51]] with U-Boot 2010.03:
<pre class="apf">
# Configuration file for fw_(printenv/saveenv) utility.
# Up to two entries are valid, in this case the redundand
# environment sector is assumed present.
# Notice, that the "Number of sectors" is ignored on NOR.
# MTD device name       Device offset   Env. size       Flash sector size       Number of sectors
/dev/mtd1                 0x0000          0x20000           0x20000                 4
</pre>

* For the [[APF9328]] with U-Boot 1.3.4:
<pre class="apf">
# Configuration file for fw_(printenv/saveenv) utility.
# Up to two entries are valid, in this case the redundand
# environment sector is assumed present.
# Notice, that the "Number of sectors" is ignored on NOR.
# MTD device name       Device offset   Env. size       Flash sector size       Number of sectors
/dev/mtd1                 0x0000          0x20000           0x20000
</pre>

* For the [[APF9328]] / [[APF27]] / [[APF28]] / [[APF51]] since U-Boot since 2012.04.01 (Armadeus-5.0 and upper):
<pre class="apf">
# Configuration file for fw_(printenv/saveenv) utility.
# Up to two entries are valid, in this case the redundant
# environment sector is assumed present.
# Notice, that the "Number of sectors" is ignored on NOR and SPI-dataflash.
# Futhermore, if the Flash sector size is ommitted, this value is assumed to
# be the same as the Environment size, which is valid for NOR and SPI-dataflash

# Armadeus boards default environment configuration
# MTD device name	Device offset	Env. size	Flash sector size	Number of sectors
/dev/mtd1                 0x0000          0x20000           0x20000                 4
/dev/mtd2                 0x0000          0x20000           0x20000                 4
</pre>

* For the [[APF6]], as it uses an [[eMMC]] and no NOR/NAND Flash, there is a custom configuration file ''/etc/fw_env_apf6.config'' that should be moved to ''/etc/fw_env.config'' before going further.
* For the [[OPOS6UL]], as it uses an [[eMMC]] and no NOR/NAND Flash, there is a custom configuration file ''/etc/fw_env_opos6ul.config'' that should be moved to ''/etc/fw_env.config'' before going further.

== Usage ==
=== Printing all the environment variables===
<pre class="apf">
# fw_printenv
bootdelay=1
baudrate=115200
ipaddr=192.168.0.2
serverip=192.168.0.1
...
</pre>

=== Printing a single environment variable ===
<pre class="apf">
# fw_printenv stdin
stdin=serial
</pre>

=== Setting and verifying an environment variable ===
* Unlock Flash access (if needed):
** On [[APF6]], you have to do this first:
<pre class="apf">
echo 0 > /sys/block/mmcblk2boot0/force_ro
</pre>
** On [[OPOS6UL]], you have to do this first:
<pre class="apf">
echo 0 > /sys/block/mmcblk0boot0/force_ro
</pre>
* Then set your variable:
<pre class="apf">
  # fw_setenv mytestvariable abcdefg
  # fw_printenv mytestvariable
  mytestenv=abcdefg
</pre>

Care must be taken when changing env variables as a typo could easily render your system unbootable. Most problems can be fixed by connecting to the serial console and using U-Boot's command line to fix bad variable.

==Links==
* This page is an adaptation on this one: http://elinux.org/U-boot_environment_variables_in_linux

[[Category: Linux]]
[[Category: U-Boot]]