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u-boot/doc/usage/environment.rst
Simon Glass b86986c7b3 video: Rename CONFIG_DM_VIDEO to CONFIG_VIDEO 
Now that all the old code is gone, rename this option. Driver model
migration is now complete.

Signed-off-by: Simon Glass <sjg@chromium.org>
2022-10-30 20:07:17 +01:00

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.. SPDX-License-Identifier: GPL-2.0+
Environment Variables
=====================
U-Boot supports user configuration using environment variables which
can be made persistent by saving to persistent storage, for example flash
memory.
Environment variables are set using "env set" (alias "setenv"), printed using
"env print" (alias "printenv"), and saved to persistent storage using
"env save" (alias "saveenv"). Using "env set"
without a value can be used to delete a variable from the
environment. As long as you don't save the environment, you are
working with an in-memory copy. In case the Flash area containing the
environment is erased by accident, a default environment is provided.
See :doc:`cmd/env` for details.
Some configuration is controlled by Environment Variables, so that setting the
variable can adjust the behaviour of U-Boot (e.g. autoboot delay, autoloading
from tftp).
Text-based Environment
----------------------
The default environment for a board is created using a `.env` environment file
using a simple text format. The base filename for this is defined by
`CONFIG_ENV_SOURCE_FILE`, or `CONFIG_SYS_BOARD` if that is empty.
The file must be in the board directory and have a .env extension, so
assuming that there is a board vendor, the resulting filename is therefore::
board/<vendor>/<board>/<CONFIG_ENV_SOURCE_FILE>.env
or::
board/<vendor>/<board>/<CONFIG_SYS_BOARD>.env
This is a plain text file where you can type your environment variables in
the form `var=value`. Blank lines and multi-line variables are supported.
The conversion script looks for a line that starts in column 1 with a string
and has an equals sign immediately afterwards. Spaces before the = are not
permitted. It is a good idea to indent your scripts so that only the 'var='
appears at the start of a line.
To add additional text to a variable you can use `var+=value`. This text is
merged into the variable during the make process and made available as a
single value to U-Boot. Variables can contain `+` characters but in the unlikely
event that you want to have a variable name ending in plus, put a backslash
before the `+` so that the script knows you are not adding to an existing
variable but assigning to a new one::
maximum\+=value
This file can include C-style comments. Blank lines and multi-line
variables are supported, and you can use normal C preprocessor directives
and CONFIG defines from your board config also.
For example, for snapper9260 you would create a text file called
`board/bluewater/snapper9260.env` containing the environment text.
Example::
stdout=serial
#ifdef CONFIG_VIDEO
stdout+=,vidconsole
#endif
bootcmd=
/* U-Boot script for booting */
if [ -z ${tftpserverip} ]; then
echo "Use 'setenv tftpserverip a.b.c.d' to set IP address."
fi
usb start; setenv autoload n; bootp;
tftpboot ${tftpserverip}:
bootm
failed=
/* Print a message when boot fails */
echo CONFIG_SYS_BOARD boot failed - please check your image
echo Load address is CONFIG_SYS_LOAD_ADDR
If CONFIG_ENV_SOURCE_FILE is empty and the default filename is not present, then
the old-style C environment is used instead. See below.
Old-style C environment
-----------------------
Traditionally, the default environment is created in `include/env_default.h`,
and can be augmented by various `CONFIG` defines. See that file for details. In
particular you can define `CONFIG_EXTRA_ENV_SETTINGS` in your board file
to add environment variables.
Board maintainers are encouraged to migrate to the text-based environment as it
is easier to maintain. The distro-board script still requires the old-style
environment but work is underway to address this.
List of environment variables
-----------------------------
Some device configuration options can be set using environment variables. In
many cases the value in the default environment comes from a CONFIG option - see
`include/env_default.h`) for this.
This is most-likely not complete:
autostart
If set to "yes" (actually any string starting with 1, y, Y, t, or T) an
image loaded with one of the commands listed below will be automatically
started by internally invoking the bootm command.
* bootelf - Boot from an ELF image in memory
* bootp - boot image via network using BOOTP/TFTP protocol
* dhcp - boot image via network using DHCP/TFTP protocol
* diskboot - boot from ide device
* nboot - boot from NAND device
* nfs - boot image via network using NFS protocol
* rarpboot - boot image via network using RARP/TFTP protocol
* scsiboot - boot from SCSI device
* tftpboot - boot image via network using TFTP protocol
* usbboot - boot from USB device
If the environment variable autostart is not set to a value starting with
1, y, Y, t, or T, an image passed to the "bootm" command will be copied to
the load address (and eventually uncompressed), but NOT be started.
This can be used to load and uncompress arbitrary data.
baudrate
Used to set the baudrate of the UART - it defaults to CONFIG_BAUDRATE (which
defaults to 115200).
bootdelay
Delay before automatically running bootcmd. During this time the user
can choose to enter the shell (or the boot menu if
CONFIG_AUTOBOOT_MENU_SHOW=y):
- 0 to autoboot with no delay, but you can stop it by key input.
- -1 to disable autoboot.
- -2 to autoboot with no delay and not check for abort
The default value is defined by CONFIG_BOOTDELAY.
The value of 'bootdelay' is overridden by the /config/bootdelay value in
the device-tree if CONFIG_OF_CONTROL=y.
bootcmd
The command that is run if the user does not enter the shell during the
boot delay.
bootargs
Command line arguments passed when booting an operating system or binary
image
bootfile
Name of the image to load with TFTP
bootm_low
Memory range available for image processing in the bootm
command can be restricted. This variable is given as
a hexadecimal number and defines lowest address allowed
for use by the bootm command. See also "bootm_size"
environment variable. Address defined by "bootm_low" is
also the base of the initial memory mapping for the Linux
kernel -- see the description of CONFIG_SYS_BOOTMAPSZ and
bootm_mapsize.
bootm_mapsize
Size of the initial memory mapping for the Linux kernel.
This variable is given as a hexadecimal number and it
defines the size of the memory region starting at base
address bootm_low that is accessible by the Linux kernel
during early boot. If unset, CONFIG_SYS_BOOTMAPSZ is used
as the default value if it is defined, and bootm_size is
used otherwise.
bootm_size
Memory range available for image processing in the bootm
command can be restricted. This variable is given as
a hexadecimal number and defines the size of the region
allowed for use by the bootm command. See also "bootm_low"
environment variable.
bootstopkeysha256, bootdelaykey, bootstopkey
See README.autoboot
updatefile
Location of the software update file on a TFTP server, used
by the automatic software update feature. Please refer to
documentation in doc/README.update for more details.
autoload
if set to "no" (any string beginning with 'n'),
"bootp" and "dhcp" will just load perform a lookup of the
configuration from the BOOTP server, but not try to
load any image.
fdt_high
if set this restricts the maximum address that the
flattened device tree will be copied into upon boot.
For example, if you have a system with 1 GB memory
at physical address 0x10000000, while Linux kernel
only recognizes the first 704 MB as low memory, you
may need to set fdt_high as 0x3C000000 to have the
device tree blob be copied to the maximum address
of the 704 MB low memory, so that Linux kernel can
access it during the boot procedure.
If this is set to the special value 0xffffffff (32-bit machines) or
0xffffffffffffffff (64-bit machines) then
the fdt will not be copied at all on boot. For this
to work it must reside in writable memory, have
sufficient padding on the end of it for u-boot to
add the information it needs into it, and the memory
must be accessible by the kernel. This usage is strongly discouraged
however as it also stops U-Boot from ensuring the device tree starting
address is properly aligned and a misaligned tree will cause OS failures.
fdtcontroladdr
if set this is the address of the control flattened
device tree used by U-Boot when CONFIG_OF_CONTROL is
defined.
initrd_high
restrict positioning of initrd images:
If this variable is not set, initrd images will be
copied to the highest possible address in RAM; this
is usually what you want since it allows for
maximum initrd size. If for some reason you want to
make sure that the initrd image is loaded below the
CONFIG_SYS_BOOTMAPSZ limit, you can set this environment
variable to a value of "no" or "off" or "0".
Alternatively, you can set it to a maximum upper
address to use (U-Boot will still check that it
does not overwrite the U-Boot stack and data).
For instance, when you have a system with 16 MB
RAM, and want to reserve 4 MB from use by Linux,
you can do this by adding "mem=12M" to the value of
the "bootargs" variable. However, now you must make
sure that the initrd image is placed in the first
12 MB as well - this can be done with::
setenv initrd_high 00c00000
If you set initrd_high to 0xffffffff (32-bit machines) or
0xffffffffffffffff (64-bit machines), this is an
indication to U-Boot that all addresses are legal
for the Linux kernel, including addresses in flash
memory. In this case U-Boot will NOT COPY the
ramdisk at all. This may be useful to reduce the
boot time on your system, but requires that this
feature is supported by your Linux kernel. This usage however requires
that the user ensure that there will be no overlap with other parts of the
image such as the Linux kernel BSS. It should not be enabled by default
and only done as part of optimizing a deployment.
ipaddr
IP address; needed for tftpboot command
loadaddr
Default load address for commands like "bootp",
"rarpboot", "tftpboot", "loadb" or "diskboot". Note that the optimal
default values here will vary between architectures. On 32bit ARM for
example, some offset from start of memory is used as the Linux kernel
zImage has a self decompressor and it's best if we stay out of where that
will be working.
loads_echo
see CONFIG_LOADS_ECHO
serverip
TFTP server IP address; needed for tftpboot command
bootretry
see CONFIG_BOOT_RETRY_TIME
bootdelaykey
see CONFIG_AUTOBOOT_DELAY_STR
bootstopkey
see CONFIG_AUTOBOOT_STOP_STR
ethprime
controls which network interface is used first.
ethact
controls which interface is currently active.
For example you can do the following::
=> setenv ethact FEC
=> ping 192.168.0.1 # traffic sent on FEC
=> setenv ethact SCC
=> ping 10.0.0.1 # traffic sent on SCC
ethrotate
When set to "no" U-Boot does not go through all
available network interfaces.
It just stays at the currently selected interface. When unset or set to
anything other than "no", U-Boot does go through all
available network interfaces.
netretry
When set to "no" each network operation will
either succeed or fail without retrying.
When set to "once" the network operation will
fail when all the available network interfaces
are tried once without success.
Useful on scripts which control the retry operation
themselves.
silent_linux
If set then Linux will be told to boot silently, by
adding 'console=' to its command line. If "yes" it will be
made silent. If "no" it will not be made silent. If
unset, then it will be made silent if the U-Boot console
is silent.
tftpsrcp
If this is set, the value is used for TFTP's
UDP source port.
tftpdstp
If this is set, the value is used for TFTP's UDP
destination port instead of the default port 69.
tftpblocksize
Block size to use for TFTP transfers; if not set,
we use the TFTP server's default block size
tftptimeout
Retransmission timeout for TFTP packets (in milli-
seconds, minimum value is 1000 = 1 second). Defines
when a packet is considered to be lost so it has to
be retransmitted. The default is 5000 = 5 seconds.
Lowering this value may make downloads succeed
faster in networks with high packet loss rates or
with unreliable TFTP servers.
tftptimeoutcountmax
maximum count of TFTP timeouts (no
unit, minimum value = 0). Defines how many timeouts
can happen during a single file transfer before that
transfer is aborted. The default is 10, and 0 means
'no timeouts allowed'. Increasing this value may help
downloads succeed with high packet loss rates, or with
unreliable TFTP servers or client hardware.
tftpwindowsize
if this is set, the value is used for TFTP's
window size as described by RFC 7440.
This means the count of blocks we can receive before
sending ack to server.
vlan
When set to a value < 4095 the traffic over
Ethernet is encapsulated/received over 802.1q
VLAN tagged frames.
Note: This appears not to be used in U-Boot. See `README.VLAN`.
bootpretryperiod
Period during which BOOTP/DHCP sends retries.
Unsigned value, in milliseconds. If not set, the period will
be either the default (28000), or a value based on
CONFIG_NET_RETRY_COUNT, if defined. This value has
precedence over the value based on CONFIG_NET_RETRY_COUNT.
memmatches
Number of matches found by the last 'ms' command, in hex
memaddr
Address of the last match found by the 'ms' command, in hex,
or 0 if none
mempos
Index position of the last match found by the 'ms' command,
in units of the size (.b, .w, .l) of the search
zbootbase
(x86 only) Base address of the bzImage 'setup' block
zbootaddr
(x86 only) Address of the loaded bzImage, typically
BZIMAGE_LOAD_ADDR which is 0x100000
Image locations
---------------
The following image location variables contain the location of images
used in booting. The "Image" column gives the role of the image and is
not an environment variable name. The other columns are environment
variable names. "File Name" gives the name of the file on a TFTP
server, "RAM Address" gives the location in RAM the image will be
loaded to, and "Flash Location" gives the image's address in NOR
flash or offset in NAND flash.
*Note* - these variables don't have to be defined for all boards, some
boards currently use other variables for these purposes, and some
boards use these variables for other purposes.
Also note that most of these variables are just a commonly used set of variable
names, used in some other variable definitions, but are not hard-coded anywhere
in U-Boot code.
================= ============== ================ ==============
Image File Name RAM Address Flash Location
================= ============== ================ ==============
Linux kernel bootfile kernel_addr_r kernel_addr
device tree blob fdtfile fdt_addr_r fdt_addr
ramdisk ramdiskfile ramdisk_addr_r ramdisk_addr
================= ============== ================ ==============
When setting the RAM addresses for `kernel_addr_r`, `fdt_addr_r` and
`ramdisk_addr_r` there are several types of constraints to keep in mind. The
one type of constraint is payload requirement. For example, a device tree MUST
be loaded at an 8-byte aligned address as that is what the specification
requires. In a similar manner, the operating system may define restrictions on
where in memory space payloads can be. This is documented for example in Linux,
with both the `Booting ARM Linux`_ and `Booting AArch64 Linux`_ documents.
Finally, there are practical constraints. We do not know the size of a given
payload a user will use but each payload must not overlap or it will corrupt
the other payload. A similar problem can happen when a payload ends up being in
the OS BSS area. For these reasons we need to ensure our default values here
are both unlikely to lead to failure to boot and sufficiently explained so that
they can be optimized for boot time or adjusted for smaller memory
configurations.
On different architectures we will have different constraints. It is important
that we follow whatever documented requirements are available to best ensure
forward compatibility. What follows are examples to highlight how to provide
reasonable default values in different cases.
Texas Instruments OMAP2PLUS (ARMv7) example
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
On these families of processors we are on a 32bit ARMv7 core. As booting some
form of Linux is our most common payload we will also keep in mind the
documented requirements for booting that Linux provides. These values are also
known to be fine for booting a number of other operating systems (or their
loaders). In this example we define the following variables and values::
loadaddr=0x82000000
kernel_addr_r=${loadaddr}
fdt_addr_r=0x88000000
ramdisk_addr_r=0x88080000
bootm_size=0x10000000
The first thing to keep in mind is that DRAM starts at 0x80000000. We set a
32MiB buffer from the start of memory as our default load address and set
``kernel_addr_r`` to that. This is because the Linux ``zImage`` decompressor
will typically then be able to avoid doing a relocation itself. It also MUST be
within the first 128MiB of memory. The next value is we set ``fdt_addr_r`` to
be at 128MiB offset from the start of memory. This location is suggested by the
kernel documentation and is exceedingly unlikely to be overwritten by the
kernel itself given other architectural constraints. We then allow for the
device tree to be up to 512KiB in size before placing the ramdisk in memory. We
then say that everything should be within the first 256MiB of memory so that
U-Boot can relocate things as needed to ensure proper alignment. We pick 256MiB
as our value here because we know there are very few platforms on in this
family with less memory. It could be as high as 768MiB and still ensure that
everything would be visible to the kernel, but again we go with what we assume
is the safest assumption.
Automatically updated variables
-------------------------------
The following environment variables may be used and automatically
updated by the network boot commands ("bootp" and "rarpboot"),
depending the information provided by your boot server:
========= ===================================================
Variable Notes
========= ===================================================
bootfile see above
dnsip IP address of your Domain Name Server
dnsip2 IP address of your secondary Domain Name Server
gatewayip IP address of the Gateway (Router) to use
hostname Target hostname
ipaddr See above
netmask Subnet Mask
rootpath Pathname of the root filesystem on the NFS server
serverip see above
========= ===================================================
Special environment variables
-----------------------------
There are two special Environment Variables:
serial#
contains hardware identification information such as type string and/or
serial number
ethaddr
Ethernet address. If CONFIG_REGEX=y, also eth*addr (where * is an integer).
These variables can be set only once (usually during manufacturing of
the board). U-Boot refuses to delete or overwrite these variables
once they have been set, unless CONFIG_ENV_OVERWRITE is enabled in the board
configuration.
Also:
ver
Contains the U-Boot version string as printed
with the "version" command. This variable is
readonly (see CONFIG_VERSION_VARIABLE).
Please note that changes to some configuration parameters may take
only effect after the next boot (yes, that's just like Windows).
External environment file
-------------------------
The `CONFIG_USE_DEFAULT_ENV_FILE` option provides a way to bypass the
environment generation in U-Boot. If enabled, then `CONFIG_DEFAULT_ENV_FILE`
provides the name of a file which is converted into the environment,
completely bypassing the standard environment variables in `env_default.h`.
The format is the same as accepted by the mkenvimage tool, with lines containing
key=value pairs. Blank lines and lines beginning with # are ignored.
Future work may unify this feature with the text-based environment, perhaps
moving the contents of `env_default.h` to a text file.
Implementation
--------------
See :doc:`../develop/environment` for internal development details.
.. _`Booting ARM Linux`: https://www.kernel.org/doc/html/latest/arm/booting.html
.. _`Booting AArch64 Linux`: https://www.kernel.org/doc/html/latest/arm64/booting.html
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