linux/Documentation/serial/n_gsm.txt
<<
>>
Prefs
   1n_gsm.c GSM 0710 tty multiplexor HOWTO
   2===================================================
   3
   4This line discipline implements the GSM 07.10 multiplexing protocol
   5detailed in the following 3GPP document :
   6http://www.3gpp.org/ftp/Specs/archive/07_series/07.10/0710-720.zip
   7
   8This document give some hints on how to use this driver with GPRS and 3G
   9modems connected to a physical serial port.
  10
  11How to use it
  12-------------
  131- initialize the modem in 0710 mux mode (usually AT+CMUX= command) through
  14its serial port. Depending on the modem used, you can pass more or less
  15parameters to this command,
  162- switch the serial line to using the n_gsm line discipline by using
  17TIOCSETD ioctl,
  183- configure the mux using GSMIOC_GETCONF / GSMIOC_SETCONF ioctl,
  19
  20Major parts of the initialization program :
  21(a good starting point is util-linux-ng/sys-utils/ldattach.c)
  22#include <linux/gsmmux.h>
  23#define N_GSM0710       21      /* GSM 0710 Mux */
  24#define DEFAULT_SPEED   B115200
  25#define SERIAL_PORT     /dev/ttyS0
  26
  27        int ldisc = N_GSM0710;
  28        struct gsm_config c;
  29        struct termios configuration;
  30
  31        /* open the serial port connected to the modem */
  32        fd = open(SERIAL_PORT, O_RDWR | O_NOCTTY | O_NDELAY);
  33
  34        /* configure the serial port : speed, flow control ... */
  35
  36        /* send the AT commands to switch the modem to CMUX mode
  37           and check that it's successful (should return OK) */
  38        write(fd, "AT+CMUX=0\r", 10);
  39
  40        /* experience showed that some modems need some time before
  41           being able to answer to the first MUX packet so a delay
  42           may be needed here in some case */
  43        sleep(3);
  44
  45        /* use n_gsm line discipline */
  46        ioctl(fd, TIOCSETD, &ldisc);
  47
  48        /* get n_gsm configuration */
  49        ioctl(fd, GSMIOC_GETCONF, &c);
  50        /* we are initiator and need encoding 0 (basic) */
  51        c.initiator = 1;
  52        c.encapsulation = 0;
  53        /* our modem defaults to a maximum size of 127 bytes */
  54        c.mru = 127;
  55        c.mtu = 127;
  56        /* set the new configuration */
  57        ioctl(fd, GSMIOC_SETCONF, &c);
  58
  59        /* and wait for ever to keep the line discipline enabled */
  60        daemon(0,0);
  61        pause();
  62
  634- create the devices corresponding to the "virtual" serial ports (take care,
  64each modem has its configuration and some DLC have dedicated functions,
  65for example GPS), starting with minor 1 (DLC0 is reserved for the management
  66of the mux)
  67
  68MAJOR=`cat /proc/devices |grep gsmtty | awk '{print $1}`
  69for i in `seq 1 4`; do
  70        mknod /dev/ttygsm$i c $MAJOR $i
  71done
  72
  735- use these devices as plain serial ports.
  74for example, it's possible :
  75- and to use gnokii to send / receive SMS on ttygsm1
  76- to use ppp to establish a datalink on ttygsm2
  77
  786- first close all virtual ports before closing the physical port.
  79
  80Additional Documentation
  81------------------------
  82More practical details on the protocol and how it's supported by industrial
  83modems can be found in the following documents :
  84http://www.telit.com/module/infopool/download.php?id=616
  85http://www.u-blox.com/images/downloads/Product_Docs/LEON-G100-G200-MuxImplementation_ApplicationNote_%28GSM%20G1-CS-10002%29.pdf
  86http://www.sierrawireless.com/Support/Downloads/AirPrime/WMP_Series/~/media/Support_Downloads/AirPrime/Application_notes/CMUX_Feature_Application_Note-Rev004.ashx
  87http://wm.sim.com/sim/News/photo/2010721161442.pdf
  88
  8911-03-08 - Eric BĂ©nard - <eric@eukrea.com>
  90
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.