2011-03-09 18:24:48 +00:00
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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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2011-03-31 01:57:33 +00:00
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and check that it's successful (should return OK) */
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2011-03-09 18:24:48 +00:00
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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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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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