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doc: Improve environment documentation

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Make various updates suggested during review of the rST conversion.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Marek Behún <marek.behun@nic.cz>
Suggested-by: Wolfgang Denk <wd@denx.de>
This commit is contained in:
Simon Glass 2021-10-21 21:08:49 -06:00 • committed by Tom Rini
parent 1df02d1d01
commit 5ba9e01a3e
2 changed files with 28 additions and 9 deletions
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36
doc/usage/environment.rst
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@ -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
================= ============== ================ ==============

1
doc/usage/index.rst
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@ -5,6 +5,7 @@ Use U-Boot
:maxdepth: 1
dfu
environment
fdt_overlays
fit
netconsole