.. _uboot-environment:

Environment
===========

U-Boot configuration and startup behaviour is defined in it's enviornment and therein held variables. While the environment's
default values are pre-defined in source, these setteings and values can be overwritten by editing the respecitive variables, either
for short term till the next reboot or permantly by writing the changed values into area in the permanent memory (NVM: NAND or eMMC).
Which in turn will loaded at boot time.

Comprehensive description of these features is available in the `DENX's online manual`_, there specifically in the
`U-Boot Environment Variables`_ section.


http://www.denx.de/wiki/view/DULG/UBootEnvVariables


Default Environments
--------------------

Following listings showing the default environment as given after factory installation, for the major groups of COM based on
NVM (NAND/eMMC) used; also given commands how to reset variables and the enviroment as a whole.


#. `NAND default environment`_
#. `eMMC default environment`_
#. `Reset of Variables`_


NAND default environment
~~~~~~~~~~~~~~~~~~~~~~~~

`eMMC default environment`_


.. code-block:: text

   TX6S U-Boot > pr

   autoload=no
   autostart=no
   baseboard=stk5-v3
   baudrate=115200
   boot_mode=nand
   bootargs=init=/linuxrc console=ttymxc0,115200 ro debug panic=1
   bootargs_jffs2=run default_bootargs;setenv bootargs ${bootargs} root=/dev/mtdblock3 rootfstype=jffs2
   bootargs_mmc=run default_bootargs;setenv bootargs ${bootargs} root=/dev/mmcblk0p2 rootwait
   bootargs_nfs=run default_bootargs;setenv bootargs ${bootargs} root=/dev/nfs nfsroot=${nfs_server}:${nfsroot},nolock ip=dhcp
   bootargs_ubifs=run default_bootargs;setenv bootargs ${bootargs} ubi.mtd=rootfs root=ubi0:rootfs rootfstype=ubifs
   bootcmd=run bootcmd_${boot_mode} bootm_cmd
   bootcmd_jffs2=setenv autostart no;run bootargs_jffs2;nboot linux
   bootcmd_mmc=setenv autostart no;run bootargs_mmc;fatload mmc 0 ${loadaddr} uImage
   bootcmd_nand=setenv autostart no;run bootargs_ubifs;nboot linux
   bootcmd_net=setenv autoload y;setenv autostart n;run bootargs_nfs;dhcp
   bootdelay=1
   bootfile=uImage
   bootm_cmd=bootm ${loadaddr} - ${fdtaddr}
   cpu_clk=792
   default_bootargs=setenv bootargs init=/linuxrc console=ttymxc0,115200 ro debug panic=1 ${append_bootargs}
   fdtaddr=11000000
   fdtsave=fdt resize;nand erase.part dtb;nand write ${fdtaddr} dtb ${fdtsize}
   loadaddr=18000000
   mtdids=nand0=gpmi-nand
   mtdparts=mtdparts=gpmi-nand:1024k@0x20000(u-boot),384k(env),6m(linux),32m(rootfs),89600k(userfs),512k@0x7f00000(dtb),512k@0x7f80000(bbt)ro
   nfsroot=/tftpboot/rootfs
   otg_mode=device
   touchpanel=tsc2007
   video_mode=VGA
   Environment size: 1485/131068 bytes


eMMC default environment
~~~~~~~~~~~~~~~~~~~~~~~~

`NAND default environment`_

.. code-block:: text

   TX6Q U-Boot > pr

   autoload=no
   autostart=no
   baseboard=stk5-v3
   baudrate=115200
   boot_mode=mmc
   bootargs=init=/linuxrc console=ttymxc0,115200 ro debug panic=1
   bootargs_jffs2=run default_bootargs;setenv bootargs ${bootargs} root=/dev/mtdblock3 rootfstype=jffs2
   bootargs_mmc=run default_bootargs;setenv bootargs ${bootargs} root=PARTUUID=${rootpart_uuid} rootwait
   bootargs_nfs=run default_bootargs;setenv bootargs ${bootargs} root=/dev/nfs nfsroot=${nfs_server}:${nfsroot},nolock ip=dhcp
   bootargs_ubifs=run default_bootargs;setenv bootargs ${bootargs} ubi.mtd=rootfs root=ubi0:rootfs rootfstype=ubifs
   bootcmd=run bootcmd_${boot_mode} bootm_cmd
   bootcmd_jffs2=setenv autostart no;run bootargs_jffs2;nboot linux
   bootcmd_mmc=setenv autostart no;run bootargs_mmc;fatload mmc 0 ${loadaddr} uImage
   bootcmd_net=setenv autoload y;setenv autostart n;run bootargs_nfs;dhcp
   bootdelay=1
   bootfile=uImage
   bootm_cmd=bootm ${loadaddr} - ${fdtaddr}
   cpu_clk=792
   default_bootargs=setenv bootargs init=/linuxrc console=ttymxc0,115200 ro debug panic=1 ${append_bootargs}
   emmc_boot_ack=1
   emmc_boot_part=1
   fdtaddr=11000000
   fdtsave=mmc partconf 0 ${emmc_boot_ack} ${emmc_boot_part} ${emmc_boot_part};mmc write ${fdtaddr} 0x680 80;mmc partconf 0 ${emmc_boot_ack} ${emmc_boot_part} 0
   loadaddr=18000000
   nfsroot=/tftpboot/rootfs
   otg_mode=device
   rootpart_uuid=0cc66cc0-02
   touchpanel=tsc2007
   video_mode=VGA
   Environment size: 1410/131068 bytes


Reset of Variables
~~~~~~~~~~~~~~~~~~

Users can reset the environment as a whole, or can reset just specific variables. Selectively resetting variables can be used to
access variables or environment settings that have been updated or added between releases.

To unset an environment variable the same common procedure as setting is used; but instead setting it to an empty string.

.. warning::

   As long as the command '``saveenv``' is not executed, changes to the environment will be lost with the next reset. In
   development this should be the preferred method.


Examples:

- Unset variable

  unset ``apppend_bootargs`` (set empty string)

  .. code-block:: text

     setenv apppend_bootargs
     saveenv


- Reset whole environment

  .. code-block:: text

     env default -a
     saveenv


- Reset specific variable

  .. code-block:: text

     env default <*variable*>
     saveenv

  e.g. resetting ``fdtsave``

  .. code-block:: text

     env default fdtsave
     save

  .. note::

     Reseting a variable that's not part of the compiled in default environment will be deleted, accompanied by the following message:
     ``WARNING: '<variable>' not in imported env, deleting it!``


.. _`U-Boot Environment Variables`: https://www.denx.de/wiki/view/DULG/UBootEnvVariables
.. _`DENX's online manual`: https://www.denx.de/wiki/view/DULG/Manual