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/*
* (C) Copyright 2001
* Dave Ellis, SIXNET, dge@sixnetio.com
*
* See file CREDITS for list of people who contributed to this
* project.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2 of
* the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston,
* MA 02111-1307 USA
*/
Using autoboot configuration options
====================================
The basic autoboot configuration options are documented in the main
U-Boot README. See it for details. They are:
bootdelay
bootcmd
CONFIG_BOOTDELAY
CONFIG_BOOTCOMMAND
Some additional options that make autoboot safer in a production
product are documented here.
Why use them?
-------------
The basic autoboot feature allows a system to automatically boot to
the real application (such as Linux) without a user having to enter
any commands. If any key is pressed before the boot delay time
expires, U-Boot stops the autoboot process, gives a U-Boot prompt
and waits forever for a command. That's a good thing if you pressed a
key because you wanted to get the prompt.
It's not so good if the key press was a stray character on the
console serial port, say because a user who knows nothing about
U-Boot pressed a key before the system had time to boot. It's even
worse on an embedded product that doesn't have a console during
normal use. The modem plugged into that console port sends a
character at the wrong time and the system hangs, with no clue as to
why it isn't working.
You might want the system to autoboot to recover after an external
configuration program stops autoboot. If the configuration program
dies or loses its connection (modems can disconnect at the worst
time) U-Boot will patiently wait forever for it to finish.
These additional configuration options can help provide a system that
boots when it should, but still allows access to U-Boot.
What they do
------------
CONFIG_BOOT_RETRY_TIME
CONFIG_BOOT_RETRY_MIN
bootretry environment variable
These options determine what happens after autoboot is
stopped and U-Boot is waiting for commands.
CONFIG_BOOT_RETRY_TIME must be defined to enable the boot
retry feature. If the environment variable 'bootretry' is
found then its value is used, otherwise the retry timeout is
CONFIG_BOOT_RETRY_TIME. CONFIG_BOOT_RETRY_MIN is optional and
defaults to CONFIG_BOOT_RETRY_TIME. All times are in seconds.
If the retry timeout is negative, the U-Boot command prompt
never times out. Otherwise it is forced to be at least
CONFIG_BOOT_RETRY_MIN seconds. If no valid U-Boot command is
entered before the specified time the boot delay sequence is
restarted. Each command that U-Boot executes restarts the
timeout.
If CONFIG_BOOT_RETRY_TIME < 0 the feature is there, but
doesn't do anything unless the environment variable
'bootretry' is >= 0.
CONFIG_AUTOBOOT_KEYED
CONFIG_AUTOBOOT_PROMPT
CONFIG_AUTOBOOT_DELAY_STR
CONFIG_AUTOBOOT_STOP_STR
CONFIG_AUTOBOOT_DELAY_STR2
CONFIG_AUTOBOOT_STOP_STR2
bootdelaykey environment variable
bootstopkey environment variable
bootdelaykey2 environment variable
bootstopkey2 environment variable
These options give more control over stopping autoboot. When
they are used a specific character or string is required to
stop or delay autoboot.
Define CONFIG_AUTOBOOT_KEYED (no value required) to enable
this group of options. CONFIG_AUTOBOOT_DELAY_STR,
CONFIG_AUTOBOOT_STOP_STR or both should be specified (or
specified by the corresponding environment variable),
otherwise there is no way to stop autoboot.
CONFIG_AUTOBOOT_PROMPT is displayed before the boot delay
selected by CONFIG_BOOTDELAY starts. If it is not defined
there is no output indicating that autoboot is in progress.
If "%d" is included, it is replaced by the number of seconds
remaining before autoboot will start, but it does not count
down the seconds. "autoboot in %d seconds\n" is a reasonable
prompt.
If CONFIG_AUTOBOOT_DELAY_STR or bootdelaykey is specified and
this string is received from console input before autoboot
starts booting, U-Boot gives a command prompt. The U-Boot
prompt will time out if CONFIG_BOOT_RETRY_TIME is used,
otherwise it never times out.
If CONFIG_AUTOBOOT_STOP_STR or bootstopkey is specified and
this string is received from console input before autoboot
starts booting, U-Boot gives a command prompt. The U-Boot
prompt never times out, even if CONFIG_BOOT_RETRY_TIME is
used.
The string recognition is not very sophisticated. If a
partial match is detected, the first non-matching character
is checked to see if starts a new match. There is no check
for a shorter partial match, so it's best if the first
character of a key string does not appear in the rest of the
string.
Using the CONFIG_AUTOBOOT_DELAY_STR2 / bootdelaykey2 and/or
CONFIG_AUTOBOOT_STOP_STR2 / bootstopkey #defines and/or
environment variables you can specify a second, alternate
string (which allows you to haw two "password" strings).
CONFIG_ZERO_BOOTDELAY_CHECK
If this option is defined, you can stop the autoboot process
by hitting a key even in that case when "bootdelay" has been
set to 0. You can set "bootdelay" to a negative value to
prevent the check for console input.
CONFIG_RESET_TO_RETRY
(Only effective when CONFIG_BOOT_RETRY_TIME is also set)
After the countdown timed out, the board will be reset to restart
again.
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