dd80fd963c
Add support for pressing 'q' to throw away any further output until the prompt is reached. Signed-off-by: Simon Glass <sjg@chromium.org>
112 lines
3.7 KiB
ReStructuredText
112 lines
3.7 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0+
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.. sectionauthor:: Paolo Scaffardi, AIRVENT SAM s.p.a - RIMINI(ITALY), arsenio@tin.it
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.. (C) Copyright 2000
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.. sectionauthor:: Simon Glass <sjg@chromium.org>
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=======================
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U-Boot console handling
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=======================
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Introduction
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------------
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At system-startup U-Boot initializes a serial console. When U-Boot
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relocates itself to RAM, all console drivers are initialized (they
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will register all detected console devices to the system for further
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use).
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If not defined in the environment, the first input device is assigned
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to the 'stdin' file, the first output one to 'stdout' and 'stderr'.
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You can use the command `coninfo` to see all registered console
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devices and their flags. You can assign a standard file (stdin,
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stdout or stderr) to any device you see in that list simply by
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assigning its name to the corresponding environment variable. For
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example::
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# Use the serial input
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setenv stdin serial
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# Use the video console
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setenv stdout vidconsole
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Do a simple `saveenv` to save the console settings in the environment
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and get them working on the next startup, too.
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How to output text to the console
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---------------------------------
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You can use the following functions to access the console:
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stdout
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- putc() - write a char to stdout
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- puts() - write a string to stdout
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- printf() - format and write a string to stdout
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stdin
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- tstc() - test for the presence of a char in stdin
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- getchar() - get a char from stdin
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stderr
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- eputc() - write a char to stderr
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- eputs() - write a string to stderr
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- eprintf() - format and write a string to stderr
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file ('stdin', 'stdout' or 'stderr')
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- fputc() - write a char to a file
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- fputs() - write a string to a file
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- fprintf() - format and write a string to a file
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- ftstc() - test for the presence of a char in file
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- fgetc() - get a char from a file
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Remember that FILE-related functions CANNOT be used before U-Boot relocation,
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which is done in `board_init_r()`.
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Pager
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-----
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U-Boot has a simple pager feature, enabled with `CONFIG_CONSOLE_PAGER`. It is
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only available if `CONFIG_CONSOLE_MUX` is also enabled.
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When activated, the pager pauses at the end of each 'page' (screenful) of
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output, shows a prompt ": Press SPACE to continue" and lets the user read the
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output. To continue to the next page, press the SPACE key. To quit paging
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without seeing further output from the current command, press 'q'.
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The pager can be bypassed by pressing 'Q' at the prompt. This disables the pager
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until the 'pager' environment variable is given a new value.
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Page Size Configuration
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~~~~~~~~~~~~~~~~~~~~~~~
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The number of lines per page is determined in the following order of priority:
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1. **Environment variable**: The `pager` environment variable (hex value)
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takes highest priority. Set to 0 to disable paging.
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2. **Video console detection**: If no environment variable is set and a video
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console is active, the pager uses the number of rows from the video console.
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3. **Serial TTY detection**: For serial consoles, the pager checks if the
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output is connected to a terminal (TTY). If not connected to a TTY, paging
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is disabled. This check works by sending a few special characters to the
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terminal and (hopefully) receiving a reply. If you are logging the output of
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U-Boot, you may see these characters in the log. Disable
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`CONFIG_SERIAL_TERM_PRESENT` is this is unwanted.
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4. **Configuration default**: If none of the above apply, falls back to
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`CONFIG_CONSOLE_PAGER_LINES`.
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Examples::
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# Set page size to 30 lines (hex value 1e)
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setenv pager 1e
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# Set page size to 24 lines (hex value 18)
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setenv pager 18
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# Disable paging
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setenv pager 0
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For developer documentation, please see :doc:`/develop/console`.
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