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