Marek VasutandHeinrich Schuchardt
dc3765ede5
The "env" command is the recommended environment management command, its "set" subcommand is the equivalent replacement for legacy "setenv" command. Update the documentation to use the contemporary "env set" command instead of legacy "setenv" command. Note that the "setenv" command is unlikely to be removed from U-Boot in the near future due to it being integral part of the command line ABI. Implemented using: $ sed -i 's@\<setenv\>@env set@g' $(git grep -li '\<setenv\>' doc/) README Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
90 lines
3.6 KiB
Plaintext
90 lines
3.6 KiB
Plaintext
SPDX-License-Identifier: GPL-2.0+
|
|
/*
|
|
* (C) Copyright 2008
|
|
* Gary Jennejohn, DENX Software Engineering GmbH <garyj@denx.de>
|
|
*/
|
|
|
|
U-Boot console multiplexing
|
|
===========================
|
|
|
|
HOW CONSOLE MULTIPLEXING WORKS
|
|
------------------------------
|
|
|
|
This functionality is controlled with CONFIG_CONSOLE_MUX in the board
|
|
configuration file.
|
|
|
|
Two new files, common/iomux.c and include/iomux.h, contain the heart
|
|
(iomux_doenv()) of the environment setting implementation.
|
|
|
|
iomux_doenv() is called in common/cmd_nvedit.c to handle env set and in
|
|
common/console.c in console_init_r() during bootup to initialize
|
|
stdio_devices[].
|
|
|
|
A user can use a comma-separated list of devices to set stdin, stdout
|
|
and stderr. For example: "env set stdin serial,nc". NOTE: No spaces
|
|
are allowed around the comma(s)!
|
|
|
|
The length of the list is limited by malloc(), since the array used
|
|
is allocated and freed dynamically.
|
|
|
|
It should be possible to specify any device which console_assign()
|
|
finds acceptable, but the code has only been tested with serial and
|
|
nc.
|
|
|
|
iomux_doenv() prevents multiple use of the same device, e.g. "env set
|
|
stdin nc,nc,serial" will discard the second nc. iomux_doenv() is
|
|
not able to modify the environment, however, so that "pri stdin" still
|
|
shows "nc,nc,serial".
|
|
|
|
The major change in common/console.c was to modify fgetc() to call
|
|
the iomux_tstc() routine in a for-loop. iomux_tstc() in turn calls
|
|
the tstc() routine for every registered device, but exits immediately
|
|
when one of them returns true. fgetc() then calls iomux_getc(),
|
|
which calls the corresponding getc() routine. fgetc() hangs in
|
|
the for-loop until iomux_tstc() returns true and the input can be
|
|
retrieved.
|
|
|
|
Thus, a user can type into any device registered for stdin. No effort
|
|
has been made to demulitplex simultaneous input from multiple stdin
|
|
devices.
|
|
|
|
fputc() and fputs() have been modified to call iomux_putc() and
|
|
iomux_puts() respectively, which call the corresponding output
|
|
routines for every registered device.
|
|
|
|
Thus, a user can see the ouput for any device registered for stdout
|
|
or stderr on all devices registered for stdout or stderr. As an
|
|
example, if stdin=serial,nc and stdout=serial,nc then all output
|
|
for serial, e.g. echos of input on serial, will appear on serial and nc.
|
|
|
|
Just as with the old console code, this statement is still true:
|
|
If not defined in the environment, the first input device is assigned
|
|
to the 'stdin' file, the first output one to 'stdout' and 'stderr'.
|
|
|
|
If CONFIG_SYS_CONSOLE_IS_IN_ENV is defined then multiple input/output
|
|
devices can be set at boot time if defined in the environment.
|
|
|
|
CAVEATS
|
|
-------
|
|
|
|
Note that common/iomux.c calls console_assign() for every registered
|
|
device as it is discovered. This means that the environment settings
|
|
for application consoles will be set to the last device in the list.
|
|
|
|
On a slow machine, such as MPC852T clocked at 66MHz, the overhead associated
|
|
with calling tstc() and then getc() means that copy&paste will normally not
|
|
work, even when stdin=stdout=stderr=serial.
|
|
On a faster machine, such as a sequoia, cut&paste of longer (about 80
|
|
characters) lines works fine when serial is the only device used.
|
|
|
|
Using nc as a stdin device results in even more overhead because nc_tstc()
|
|
is quite slow. Even on a sequoia cut&paste does not work on the serial
|
|
interface when nc is added to stdin, although there is no character loss using
|
|
the ethernet interface for input. In this test case stdin=serial,nc and
|
|
stdout=serial.
|
|
|
|
In addition, the overhead associated with sending to two devices, when one of
|
|
them is nc, also causes problems. Even on a sequoia cut&paste does not work
|
|
on the serial interface (stdin=serial) when nc is added to stdout (stdout=
|
|
serial,nc).
|