diff options
author | Gary Jennejohn <garyj@denx.de> | 2008-11-06 15:04:23 +0100 |
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committer | Wolfgang Denk <wd@denx.de> | 2008-12-07 01:23:35 +0100 |
commit | 16a28ef219c27423a1ef502f19070c4d375079b8 (patch) | |
tree | 2241bdb2293824bdb7b82e1ff8d54e9246c81bcc /doc | |
parent | 774ce72026f74ac9641bcbbc588b20f2e13f7ab8 (diff) |
IOMUX: Add console multiplexing support.
Modifications to support console multiplexing. This is controlled using
CONFIG_SYS_CONSOLE_MUX in the board configuration file.
This allows a user to specify multiple console devices in the environment
with a command like this: setenv stdin serial,nc. As a result, the user can
enter text on both the serial and netconsole interfaces.
All devices - stdin, stdout and stderr - can be set in this manner.
1) common/iomux.c and include/iomux.h contain the environment setting
implementation.
2) doc/README.iomux contains a somewhat more detailed description.
3) The implementation in (1) is called from common/cmd_nvedit.c to
handle setenv and from common/console.c to handle initialization of
input/output devices at boot time.
4) common/console.c also contains the code needed to poll multiple console
devices for input and send output to all devices registered for output.
5) include/common.h includes iomux.h and common/Makefile generates iomux.o
when CONFIG_SYS_CONSOLE_MUX is set.
Signed-off-by: Gary Jennejohn <garyj@denx.de>
Diffstat (limited to 'doc')
-rw-r--r-- | doc/README.iomux | 106 |
1 files changed, 106 insertions, 0 deletions
diff --git a/doc/README.iomux b/doc/README.iomux new file mode 100644 index 0000000000..5b82a86672 --- /dev/null +++ b/doc/README.iomux @@ -0,0 +1,106 @@ +/* + * (C) Copyright 2008 + * Gary Jennejohn, DENX Software Engineering GmbH <garyj@denx.de> + * + * 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 + */ + +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 setenv 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: "setenv 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. "setenv +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). |