From: Simon Glass Date: Fri, 22 Oct 2021 03:08:49 +0000 (-0600) Subject: doc: Improve environment documentation X-Git-Url: http://git.dujemihanovic.xyz/login.html?a=commitdiff_plain;h=5ba9e01a3e70985e5839d941b307b894c13d78dc;p=u-boot.git doc: Improve environment documentation Make various updates suggested during review of the rST conversion. Signed-off-by: Simon Glass Reviewed-by: Marek Behún Suggested-by: Wolfgang Denk --- diff --git a/doc/usage/environment.rst b/doc/usage/environment.rst index 6f3066e2b6..af193739a5 100644 --- a/doc/usage/environment.rst +++ b/doc/usage/environment.rst @@ -4,16 +4,20 @@ Environment Variables ===================== U-Boot supports user configuration using Environment Variables which -can be made persistent by saving to Flash memory. +can be made persistent by saving to persistent storage, for example flash +memory. -Environment Variables are set using "setenv", printed using -"printenv", and saved to Flash using "saveenv". Using "setenv" +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 +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 options can be set using Environment Variables. +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 ---------------------- @@ -94,16 +98,24 @@ environment but work is underway to address this. List of environment variables ----------------------------- +Some 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 - see CONFIG_BAUDRATE + Current baud rate used by the serial console. The built-in value is set by + CONFIG_BAUDRATE (see `drivers/serial/Kconfig`) bootdelay - see CONFIG_BOOTDELAY + Current autoboot delay. The built-in value is set by CONFIG_BOOTDELAY (see + `common/Kconfig`) bootcmd - see CONFIG_BOOTCOMMAND + Defines a command string that is automatically executed when no character + is read on the console interface within a cetain boot delay after reset. + The built-in value is set by CONFIG_BOOTCOMMAND (see `common/Kconfig`) bootargs Boot arguments when booting an RTOS image @@ -149,7 +161,7 @@ autoload if set to "no" (any string beginning with 'n'), "bootp" will just load perform a lookup of the configuration from the BOOTP server, but not try to - load any image using TFTP + load any image using TFTP or DHCP. autostart if set to "yes", an image loaded using the "bootp", @@ -315,6 +327,8 @@ vlan 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 @@ -356,6 +370,10 @@ flash or offset in NAND flash. 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 ================= ============== ================ ============== diff --git a/doc/usage/index.rst b/doc/usage/index.rst index 4314112ff3..04dea9f0f8 100644 --- a/doc/usage/index.rst +++ b/doc/usage/index.rst @@ -5,6 +5,7 @@ Use U-Boot :maxdepth: 1 dfu + environment fdt_overlays fit netconsole