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diff --git a/doc/usage/environment.rst b/doc/usage/environment.rst new file mode 100644 index 0000000000..d295cc8987 --- /dev/null +++ b/doc/usage/environment.rst @@ -0,0 +1,465 @@ +.. 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. + +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_LCD + stdout+=,lcd + #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: + +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. + Does it really make sense that the devicetree overrides the user setting? + +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 using TFTP or DHCP. + +autostart + if set to "yes", an image loaded using the "bootp", "dhcp", + "rarpboot", "tftpboot" or "diskboot" commands will + be automatically started (by internally calling + "bootm") + + If unset, or set to "1"/"yes"/"true" (case insensitive, just the first + character is enough), a standalone 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. + +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. + +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. + +ipaddr + IP address; needed for tftpboot command + +loadaddr + Default load address for commands like "bootp", + "rarpboot", "tftpboot", "loadb" or "diskboot" + +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 valu 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 +================= ============== ================ ============== +u-boot u-boot u-boot_addr_r u-boot_addr +Linux kernel bootfile kernel_addr_r kernel_addr +device tree blob fdtfile fdt_addr_r fdt_addr +ramdisk ramdiskfile ramdisk_addr_r ramdisk_addr +================= ============== ================ ============== + + +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. |