SPDX-License-Identifier: GPL-2.0+ /* * (C) Copyright 2001 * Dave Ellis, SIXNET, dge@sixnetio.com * */ 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 "bootdelaykey" environment variable "bootstopkey" 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. 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_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.