XELK-AN-006: Modify u-boot environment from userspace

Info Box Applies to Axel Ultra Applies to AXEL ESATTA Applies to Axel Lite

This application note was validated against specific versions of the kit only. It may not work with other versions. Supported versions are listed in the History section.

History

Version	Date	Notes
1.0.0	June 2019	First release

Introduction

Axel family system-on-modules (SOM for short) are based on u-boot and linux BSP which is configured - at boot time - using the u-boot environment variables configuration.

Many times, it should ve very useful to modify the u-boot environment from linux userspace access. This is possible using the fw_printenv and fw_setenv utilities present on u-boot source codes.

Tools required

In order to modify the uboot environment variables from userspace the fw_printenv has to be compiled from the u-boot sources: this is possible using the

make env

command on u-boot source code tree

Once built, the second utility fw_setenv is just a copy of the built one: the tool itself, uses the recognized file name for identifying if accessing in print or set mode the u-boot environment.

Configuration file

fw_printenv uses the /etc/fw_env.config configuration file for identifying the correct parameters to access the storage device where the u-boot environment is memorized.

Please find below an example on how to identify the u-boot storage device and its configuration:

MTDs

Using the

cat /proc/mtd

command, it is possible to see the memory partitioning and where the environment parts are:

root@imx6qxelk:~# cat /proc/mtd
dev:    size   erasesize  name
mtd0: 00800000 00020000 "nand-uboot"
mtd1: 00100000 00020000 "nand-env1"
mtd2: 00100000 00020000 "nand-env2"
mtd3: 00100000 00020000 "nand-fdt"
mtd4: 00100000 00020000 "nand-spare"
mtd5: 00800000 00020000 "nand-kernel"
mtd6: 00400000 00020000 "nand-splash"
mtd7: 3e800000 00020000 "nand-ubi"
root@imx6qxelk:~#

So, in this example we can see that the two mtd parts to be used are

mtd1: 00100000 00020000 "nand-env1"
mtd2: 00100000 00020000 "nand-env2"

Sizes

The two parameters required for properly configuring the fw_env.config file are:

• Env. size
• Flash sector size

Those values are identifyed at compile time into the proper header file used for building u-boot. On AxelLite family this file is include/configs/mx6axel.h and the parameters should be found according to the storage device used.

For example, if the boot storage device is a NAND memory, the config var is:

CONFIG_ENV_IS_IN_NAND

and the related section (for the environment sizes) is:

#elif defined(CONFIG_ENV_IS_IN_NAND)
#undef CONFIG_ENV_SIZE
#define CONFIG_ENV_OFFSET			(8 * 1024 * 1024)
#define CONFIG_ENV_SECT_SIZE			(1 * 1024 * 1024)
#define CONFIG_ENV_SIZE				(128 * 1024)

So, we found that the proper parameters are:

• Env. size: 0x20000
• Flash sector size: 0x100000

fw_env.config

Following the configuration information found before, we can set the proper parameters into the fw_env.config file as shown below:

root@imx6qxelk:~# cat /etc/fw_env.config
# Configuration file for fw_(printenv/setenv) utility.
# Up to two entries are valid, in this case the redundant
# environment sector is assumed present.
# Notice, that the "Number of sectors" is not required 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

# NOR example
# MTD device name       Device offset   Env. size       Flash sector size       Number of sectors
/dev/mtd1               0x0000          0x20000         0x100000
/dev/mtd2               0x0000          0x20000         0x100000

root@imx6qxelk:~#

u-boot environment access example

• display the ipaddr and bootfile environment variables:

root@imx6qxelk:~# fw_printenv ipaddr bootfile
ipaddr=192.168.0.90
bootfile=axel/linux/xelk-3.0.7_uImage
root@imx6qxelk:~#

Wrong configuration file

If some parameters are not correctly configured on the fw_env.config file, the utilities displays an error message:

Warning: Bad CRC, using default environment

It is possible to detect this situation using the return code of fw_printenv:

• fw_env.config correct file

root@imx6qxelk:~# fw_printenv ipaddr
ipaddr=192.168.0.90
root@imx6qxelk:~# echo $?
0
root@imx6qxelk:~#

• wrong fw_env.config file

root@imx6qxelk:~# fw_printenv ipaddr
Warning: Bad CRC, using default environment
## Error: "ipaddr" not defined
root@imx6qxelk:~# echo $?
1
root@imx6qxelk:~#

Command syntax

• print the whole environment

fw_printenv

• print a specific environment variable

fw_printenv <varname>

• delete environment variable

fw_setenv <varname>

• set environment variable

fw_setenv <varname> <varvalue>