3 * Dave Ellis, SIXNET, dge@sixnetio.com
5 * See file CREDITS for list of people who contributed to this
8 * This program is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU General Public License as
10 * published by the Free Software Foundation; either version 2 of
11 * the License, or (at your option) any later version.
13 * This program is distributed in the hope that it will be useful,
14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 * GNU General Public License for more details.
18 * You should have received a copy of the GNU General Public License
19 * along with this program; if not, write to the Free Software
20 * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
24 Using autoboot configuration options
25 ====================================
27 The basic autoboot configuration options are documented in the main
28 U-Boot README. See it for details. They are:
35 Some additional options that make autoboot safer in a production
36 product are documented here.
41 The basic autoboot feature allows a system to automatically boot to
42 the real application (such as Linux) without a user having to enter
43 any commands. If any key is pressed before the boot delay time
44 expires, U-Boot stops the autoboot process, gives a U-Boot prompt
45 and waits forever for a command. That's a good thing if you pressed a
46 key because you wanted to get the prompt.
48 It's not so good if the key press was a stray character on the
49 console serial port, say because a user who knows nothing about
50 U-Boot pressed a key before the system had time to boot. It's even
51 worse on an embedded product that doesn't have a console during
52 normal use. The modem plugged into that console port sends a
53 character at the wrong time and the system hangs, with no clue as to
56 You might want the system to autoboot to recover after an external
57 configuration program stops autoboot. If the configuration program
58 dies or loses its connection (modems can disconnect at the worst
59 time) U-Boot will patiently wait forever for it to finish.
61 These additional configuration options can help provide a system that
62 boots when it should, but still allows access to U-Boot.
67 CONFIG_BOOT_RETRY_TIME
70 bootretry environment variable
72 These options determine what happens after autoboot is
73 stopped and U-Boot is waiting for commands.
75 CONFIG_BOOT_RETRY_TIME must be defined to enable the boot
76 retry feature. If the environment variable 'bootretry' is
77 found then its value is used, otherwise the retry timeout is
78 CONFIG_BOOT_RETRY_TIME. CONFIG_BOOT_RETRY_MIN is optional and
79 defaults to CONFIG_BOOT_RETRY_TIME. All times are in seconds.
81 If the retry timeout is negative, the U-Boot command prompt
82 never times out. Otherwise it is forced to be at least
83 CONFIG_BOOT_RETRY_MIN seconds. If no valid U-Boot command is
84 entered before the specified time the boot delay sequence is
85 restarted. Each command that U-Boot executes restarts the
88 If CONFIG_BOOT_RETRY_TIME < 0 the feature is there, but
89 doesn't do anything unless the environment variable
93 CONFIG_AUTOBOOT_PROMPT
94 CONFIG_AUTOBOOT_DELAY_STR
95 CONFIG_AUTOBOOT_STOP_STR
96 CONFIG_AUTOBOOT_DELAY_STR2
97 CONFIG_AUTOBOOT_STOP_STR2
99 bootdelaykey environment variable
100 bootstopkey environment variable
101 bootdelaykey2 environment variable
102 bootstopkey2 environment variable
104 These options give more control over stopping autoboot. When
105 they are used a specific character or string is required to
106 stop or delay autoboot.
108 Define CONFIG_AUTOBOOT_KEYED (no value required) to enable
109 this group of options. CONFIG_AUTOBOOT_DELAY_STR,
110 CONFIG_AUTOBOOT_STOP_STR or both should be specified (or
111 specified by the corresponding environment variable),
112 otherwise there is no way to stop autoboot.
114 CONFIG_AUTOBOOT_PROMPT is displayed before the boot delay
115 selected by CONFIG_BOOTDELAY starts. If it is not defined
116 there is no output indicating that autoboot is in progress.
117 If "%d" is included, it is replaced by the number of seconds
118 remaining before autoboot will start, but it does not count
119 down the seconds. "autoboot in %d seconds\n" is a reasonable
122 If CONFIG_AUTOBOOT_DELAY_STR or bootdelaykey is specified and
123 this string is received from console input before autoboot
124 starts booting, U-Boot gives a command prompt. The U-Boot
125 prompt will time out if CONFIG_BOOT_RETRY_TIME is used,
126 otherwise it never times out.
128 If CONFIG_AUTOBOOT_STOP_STR or bootstopkey is specified and
129 this string is received from console input before autoboot
130 starts booting, U-Boot gives a command prompt. The U-Boot
131 prompt never times out, even if CONFIG_BOOT_RETRY_TIME is
134 The string recognition is not very sophisticated. If a
135 partial match is detected, the first non-matching character
136 is checked to see if starts a new match. There is no check
137 for a shorter partial match, so it's best if the first
138 character of a key string does not appear in the rest of the
141 Using the CONFIG_AUTOBOOT_DELAY_STR2 / bootdelaykey2 and/or
142 CONFIG_AUTOBOOT_STOP_STR2 / bootstopkey #defines and/or
143 environment variables you can specify a second, alternate
144 string (which allows you to have two "password" strings).
146 CONFIG_ZERO_BOOTDELAY_CHECK
148 If this option is defined, you can stop the autoboot process
149 by hitting a key even in that case when "bootdelay" has been
150 set to 0. You can set "bootdelay" to a negative value to
151 prevent the check for console input.
153 CONFIG_RESET_TO_RETRY
155 (Only effective when CONFIG_BOOT_RETRY_TIME is also set)
156 After the countdown timed out, the board will be reset to restart