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Diffstat (limited to 'doc/README.autoboot')
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diff --git a/doc/README.autoboot b/doc/README.autoboot new file mode 100644 index 000000000..20736ca47 --- /dev/null +++ b/doc/README.autoboot @@ -0,0 +1,158 @@ +/* + * (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. + |