140 lines
5.0 KiB
Plaintext
140 lines
5.0 KiB
Plaintext
SPDX-License-Identifier: GPL-2.0+
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/*
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* (C) Copyright 2001
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* Dave Ellis, SIXNET, dge@sixnetio.com
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*
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*/
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Using autoboot configuration options
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====================================
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The basic autoboot configuration options are documented in the main
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U-Boot README. See it for details. They are:
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bootdelay
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bootcmd
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CONFIG_BOOTDELAY
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CONFIG_BOOTCOMMAND
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Some additional options that make autoboot safer in a production
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product are documented here.
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Why use them?
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-------------
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The basic autoboot feature allows a system to automatically boot to
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the real application (such as Linux) without a user having to enter
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any commands. If any key is pressed before the boot delay time
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expires, U-Boot stops the autoboot process, gives a U-Boot prompt
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and waits forever for a command. That's a good thing if you pressed a
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key because you wanted to get the prompt.
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It's not so good if the key press was a stray character on the
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console serial port, say because a user who knows nothing about
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U-Boot pressed a key before the system had time to boot. It's even
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worse on an embedded product that doesn't have a console during
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normal use. The modem plugged into that console port sends a
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character at the wrong time and the system hangs, with no clue as to
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why it isn't working.
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You might want the system to autoboot to recover after an external
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configuration program stops autoboot. If the configuration program
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dies or loses its connection (modems can disconnect at the worst
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time) U-Boot will patiently wait forever for it to finish.
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These additional configuration options can help provide a system that
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boots when it should, but still allows access to U-Boot.
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What they do
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------------
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CONFIG_BOOT_RETRY_TIME
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CONFIG_BOOT_RETRY_MIN
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"bootretry" environment variable
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These options determine what happens after autoboot is
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stopped and U-Boot is waiting for commands.
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CONFIG_BOOT_RETRY_TIME must be defined to enable the boot
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retry feature. If the environment variable "bootretry" is
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found then its value is used, otherwise the retry timeout is
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CONFIG_BOOT_RETRY_TIME. CONFIG_BOOT_RETRY_MIN is optional and
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defaults to CONFIG_BOOT_RETRY_TIME. All times are in seconds.
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If the retry timeout is negative, the U-Boot command prompt
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never times out. Otherwise it is forced to be at least
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CONFIG_BOOT_RETRY_MIN seconds. If no valid U-Boot command is
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entered before the specified time the boot delay sequence is
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restarted. Each command that U-Boot executes restarts the
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timeout.
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If CONFIG_BOOT_RETRY_TIME < 0 the feature is there, but
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doesn't do anything unless the environment variable
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"bootretry" is >= 0.
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CONFIG_AUTOBOOT_KEYED
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CONFIG_AUTOBOOT_KEYED_CTRLC
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CONFIG_AUTOBOOT_PROMPT
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CONFIG_AUTOBOOT_DELAY_STR
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CONFIG_AUTOBOOT_STOP_STR
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"bootdelaykey" environment variable
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"bootstopkey" environment variable
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These options give more control over stopping autoboot. When
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they are used a specific character or string is required to
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stop or delay autoboot.
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Define CONFIG_AUTOBOOT_KEYED (no value required) to enable
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this group of options. CONFIG_AUTOBOOT_DELAY_STR,
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CONFIG_AUTOBOOT_STOP_STR or both should be specified (or
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specified by the corresponding environment variable),
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otherwise there is no way to stop autoboot.
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CONFIG_AUTOBOOT_PROMPT is displayed before the boot delay
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selected by CONFIG_BOOTDELAY starts. If it is not defined
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there is no output indicating that autoboot is in progress.
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Note that CONFIG_AUTOBOOT_PROMPT is used as the (only)
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argument to a printf() call, so it may contain '%' format
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specifications, provided that it also includes, sepearated by
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commas exactly like in a printf statement, the required
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arguments. It is the responsibility of the user to select only
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such arguments that are valid in the given context. A
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reasonable prompt could be defined as
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#define CONFIG_AUTOBOOT_PROMPT \
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"autoboot in %d seconds\n",bootdelay
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If CONFIG_AUTOBOOT_DELAY_STR or "bootdelaykey" is specified
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and this string is received from console input before
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autoboot starts booting, U-Boot gives a command prompt. The
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U-Boot prompt will time out if CONFIG_BOOT_RETRY_TIME is
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used, otherwise it never times out.
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If CONFIG_AUTOBOOT_STOP_STR or "bootstopkey" is specified and
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this string is received from console input before autoboot
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starts booting, U-Boot gives a command prompt. The U-Boot
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prompt never times out, even if CONFIG_BOOT_RETRY_TIME is
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used.
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The string recognition is not very sophisticated. If a
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partial match is detected, the first non-matching character
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is checked to see if starts a new match. There is no check
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for a shorter partial match, so it's best if the first
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character of a key string does not appear in the rest of the
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string.
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The CONFIG_AUTOBOOT_KEYED_CTRLC #define allows for the boot
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sequence to be interrupted by ctrl-c, in addition to the
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"bootdelaykey" and "bootstopkey". Setting this variable
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provides an escape sequence from the limited "password"
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strings.
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CONFIG_RESET_TO_RETRY
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(Only effective when CONFIG_BOOT_RETRY_TIME is also set)
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After the countdown timed out, the board will be reset to restart
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again.
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