/*
   * (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
  ",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.