--- /dev/null
+/*
+ * (C) Copyright 2001
+ * Dave Ellis, SIXNET, dge@sixnetio.com
+ *
+ * SPDX-License-Identifier: GPL-2.0+
+ */
+
+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_KEYED_CTRLC
+ 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.
+
+ Note that CONFIG_AUTOBOOT_PROMPT is used as the (only)
+ argument to a printf() call, so it may contain '%' format
+ specifications, provided that it also includes, sepearated by
+ commas exactly like in a printf statement, the required
+ arguments. It is the responsibility of the user to select only
+ such arguments that are valid in the given context. A
+ reasonable prompt could be defined as
+
+ #define CONFIG_AUTOBOOT_PROMPT \
+ "autoboot in %d seconds\n",bootdelay
+
+ 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 #define or the
+ "bootdelaykey2" environment variable and/or the
+ CONFIG_AUTOBOOT_STOP_STR2 #define or the "bootstopkey"
+ environment variable you can specify a second, alternate
+ string (which allows you to have two "password" strings).
+
+ The CONFIG_AUTOBOOT_KEYED_CTRLC #define allows for the boot
+ sequence to be interrupted by ctrl-c, in addition to the
+ "bootdelaykey" and "bootstopkey". Setting this variable
+ provides an escape sequence from the limited "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.
Code Review / kvmfornfv.git / blobdiff