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gsm_cleanup_mux() is called in the line discipline close path which is called at tty_release() time. At this stage the tty is no longer operational enough to send any frames. Sending close frames is therefore not possible and waiting for their answers always times out. This patch removes sending close messages and waiting for their answers from the tty_release path. This patch makes explicit what previously implicitly had been the case already: We are not able to tell the modem that we are about to close the multiplexer on our side. This means the modem will stay in multiplexer mode and re-establishing the multiplexer later fails. The only way for userspace to work around this is to manually send a close frame in N_TTY mode after closing the mux. Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
97 lines
3.6 KiB
Plaintext
97 lines
3.6 KiB
Plaintext
n_gsm.c GSM 0710 tty multiplexor HOWTO
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===================================================
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This line discipline implements the GSM 07.10 multiplexing protocol
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detailed in the following 3GPP document :
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http://www.3gpp.org/ftp/Specs/archive/07_series/07.10/0710-720.zip
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This document give some hints on how to use this driver with GPRS and 3G
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modems connected to a physical serial port.
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How to use it
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-------------
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1- initialize the modem in 0710 mux mode (usually AT+CMUX= command) through
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its serial port. Depending on the modem used, you can pass more or less
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parameters to this command,
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2- switch the serial line to using the n_gsm line discipline by using
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TIOCSETD ioctl,
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3- configure the mux using GSMIOC_GETCONF / GSMIOC_SETCONF ioctl,
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Major parts of the initialization program :
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(a good starting point is util-linux-ng/sys-utils/ldattach.c)
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#include <linux/gsmmux.h>
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#define N_GSM0710 21 /* GSM 0710 Mux */
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#define DEFAULT_SPEED B115200
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#define SERIAL_PORT /dev/ttyS0
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int ldisc = N_GSM0710;
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struct gsm_config c;
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struct termios configuration;
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/* open the serial port connected to the modem */
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fd = open(SERIAL_PORT, O_RDWR | O_NOCTTY | O_NDELAY);
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/* configure the serial port : speed, flow control ... */
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/* send the AT commands to switch the modem to CMUX mode
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and check that it's successful (should return OK) */
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write(fd, "AT+CMUX=0\r", 10);
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/* experience showed that some modems need some time before
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being able to answer to the first MUX packet so a delay
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may be needed here in some case */
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sleep(3);
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/* use n_gsm line discipline */
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ioctl(fd, TIOCSETD, &ldisc);
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/* get n_gsm configuration */
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ioctl(fd, GSMIOC_GETCONF, &c);
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/* we are initiator and need encoding 0 (basic) */
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c.initiator = 1;
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c.encapsulation = 0;
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/* our modem defaults to a maximum size of 127 bytes */
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c.mru = 127;
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c.mtu = 127;
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/* set the new configuration */
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ioctl(fd, GSMIOC_SETCONF, &c);
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/* and wait for ever to keep the line discipline enabled */
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daemon(0,0);
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pause();
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4- create the devices corresponding to the "virtual" serial ports (take care,
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each modem has its configuration and some DLC have dedicated functions,
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for example GPS), starting with minor 1 (DLC0 is reserved for the management
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of the mux)
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MAJOR=`cat /proc/devices |grep gsmtty | awk '{print $1}`
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for i in `seq 1 4`; do
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mknod /dev/ttygsm$i c $MAJOR $i
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done
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5- use these devices as plain serial ports.
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for example, it's possible :
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- and to use gnokii to send / receive SMS on ttygsm1
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- to use ppp to establish a datalink on ttygsm2
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6- first close all virtual ports before closing the physical port.
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Note that after closing the physical port the modem is still in multiplexing
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mode. This may prevent a successful re-opening of the port later. To avoid
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this situation either reset the modem if your hardware allows that or send
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a disconnect command frame manually before initializing the multiplexing mode
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for the second time. The byte sequence for the disconnect command frame is:
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0xf9, 0x03, 0xef, 0x03, 0xc3, 0x16, 0xf9.
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Additional Documentation
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------------------------
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More practical details on the protocol and how it's supported by industrial
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modems can be found in the following documents :
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http://www.telit.com/module/infopool/download.php?id=616
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http://www.u-blox.com/images/downloads/Product_Docs/LEON-G100-G200-MuxImplementation_ApplicationNote_%28GSM%20G1-CS-10002%29.pdf
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http://www.sierrawireless.com/Support/Downloads/AirPrime/WMP_Series/~/media/Support_Downloads/AirPrime/Application_notes/CMUX_Feature_Application_Note-Rev004.ashx
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http://wm.sim.com/sim/News/photo/2010721161442.pdf
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11-03-08 - Eric Bénard - <eric@eukrea.com>
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