Git Repo - u-boot.git/blame_incremental

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Commit	Line	Data
	1	/*
	2	* (C) Copyright 2001
	3	* Dave Ellis, SIXNET, [email protected]
	4	*
	5	* SPDX-License-Identifier: GPL-2.0+
	6	*/
	7
	8	Using autoboot configuration options
	9	====================================
	10
	11	The basic autoboot configuration options are documented in the main
	12	U-Boot README. See it for details. They are:
	13
	14	bootdelay
	15	bootcmd
	16	CONFIG_BOOTDELAY
	17	CONFIG_BOOTCOMMAND
	18
	19	Some additional options that make autoboot safer in a production
	20	product are documented here.
	21
	22	Why use them?
	23	-------------
	24
	25	The basic autoboot feature allows a system to automatically boot to
	26	the real application (such as Linux) without a user having to enter
	27	any commands. If any key is pressed before the boot delay time
	28	expires, U-Boot stops the autoboot process, gives a U-Boot prompt
	29	and waits forever for a command. That's a good thing if you pressed a
	30	key because you wanted to get the prompt.
	31
	32	It's not so good if the key press was a stray character on the
	33	console serial port, say because a user who knows nothing about
	34	U-Boot pressed a key before the system had time to boot. It's even
	35	worse on an embedded product that doesn't have a console during
	36	normal use. The modem plugged into that console port sends a
	37	character at the wrong time and the system hangs, with no clue as to
	38	why it isn't working.
	39
	40	You might want the system to autoboot to recover after an external
	41	configuration program stops autoboot. If the configuration program
	42	dies or loses its connection (modems can disconnect at the worst
	43	time) U-Boot will patiently wait forever for it to finish.
	44
	45	These additional configuration options can help provide a system that
	46	boots when it should, but still allows access to U-Boot.
	47
	48	What they do
	49	------------
	50
	51	CONFIG_BOOT_RETRY_TIME
	52	CONFIG_BOOT_RETRY_MIN
	53
	54	"bootretry" environment variable
	55
	56	These options determine what happens after autoboot is
	57	stopped and U-Boot is waiting for commands.
	58
	59	CONFIG_BOOT_RETRY_TIME must be defined to enable the boot
	60	retry feature. If the environment variable "bootretry" is
	61	found then its value is used, otherwise the retry timeout is
	62	CONFIG_BOOT_RETRY_TIME. CONFIG_BOOT_RETRY_MIN is optional and
	63	defaults to CONFIG_BOOT_RETRY_TIME. All times are in seconds.
	64
	65	If the retry timeout is negative, the U-Boot command prompt
	66	never times out. Otherwise it is forced to be at least
	67	CONFIG_BOOT_RETRY_MIN seconds. If no valid U-Boot command is
	68	entered before the specified time the boot delay sequence is
	69	restarted. Each command that U-Boot executes restarts the
	70	timeout.
	71
	72	If CONFIG_BOOT_RETRY_TIME < 0 the feature is there, but
	73	doesn't do anything unless the environment variable
	74	"bootretry" is >= 0.
	75
	76	CONFIG_AUTOBOOT_KEYED
	77	CONFIG_AUTOBOOT_KEYED_CTRLC
	78	CONFIG_AUTOBOOT_PROMPT
	79	CONFIG_AUTOBOOT_DELAY_STR
	80	CONFIG_AUTOBOOT_STOP_STR
	81
	82	"bootdelaykey" environment variable
	83	"bootstopkey" environment variable
	84
	85	These options give more control over stopping autoboot. When
	86	they are used a specific character or string is required to
	87	stop or delay autoboot.
	88
	89	Define CONFIG_AUTOBOOT_KEYED (no value required) to enable
	90	this group of options. CONFIG_AUTOBOOT_DELAY_STR,
	91	CONFIG_AUTOBOOT_STOP_STR or both should be specified (or
	92	specified by the corresponding environment variable),
	93	otherwise there is no way to stop autoboot.
	94
	95	CONFIG_AUTOBOOT_PROMPT is displayed before the boot delay
	96	selected by CONFIG_BOOTDELAY starts. If it is not defined
	97	there is no output indicating that autoboot is in progress.
	98
	99	Note that CONFIG_AUTOBOOT_PROMPT is used as the (only)
	100	argument to a printf() call, so it may contain '%' format
	101	specifications, provided that it also includes, sepearated by
	102	commas exactly like in a printf statement, the required
	103	arguments. It is the responsibility of the user to select only
	104	such arguments that are valid in the given context. A
	105	reasonable prompt could be defined as
	106
	107	#define CONFIG_AUTOBOOT_PROMPT \
	108	"autoboot in %d seconds\n",bootdelay
	109
	110	If CONFIG_AUTOBOOT_DELAY_STR or "bootdelaykey" is specified
	111	and this string is received from console input before
	112	autoboot starts booting, U-Boot gives a command prompt. The
	113	U-Boot prompt will time out if CONFIG_BOOT_RETRY_TIME is
	114	used, otherwise it never times out.
	115
	116	If CONFIG_AUTOBOOT_STOP_STR or "bootstopkey" is specified and
	117	this string is received from console input before autoboot
	118	starts booting, U-Boot gives a command prompt. The U-Boot
	119	prompt never times out, even if CONFIG_BOOT_RETRY_TIME is
	120	used.
	121
	122	The string recognition is not very sophisticated. If a
	123	partial match is detected, the first non-matching character
	124	is checked to see if starts a new match. There is no check
	125	for a shorter partial match, so it's best if the first
	126	character of a key string does not appear in the rest of the
	127	string.
	128
	129	The CONFIG_AUTOBOOT_KEYED_CTRLC #define allows for the boot
	130	sequence to be interrupted by ctrl-c, in addition to the
	131	"bootdelaykey" and "bootstopkey". Setting this variable
	132	provides an escape sequence from the limited "password"
	133	strings.
	134
	135	CONFIG_RESET_TO_RETRY
	136
	137	(Only effective when CONFIG_BOOT_RETRY_TIME is also set)
	138	After the countdown timed out, the board will be reset to restart
	139	again.