Documentation/serial/n_gsm.txt

   1 n_gsm.c GSM 0710 tty multiplexor HOWTO
   2 ===================================================
   3
   4 This line discipline implements the GSM 07.10 multiplexing protocol
   5 detailed in the following 3GPP document :
   6 http://www.3gpp.org/ftp/Specs/archive/07_series/07.10/0710-720.zip
   7
   8 This document give some hints on how to use this driver with GPRS and 3G
   9 modems connected to a physical serial port.
  10
  11 How to use it
  12 -------------
  13 1- initialize the modem in 0710 mux mode (usually AT+CMUX= command) through
  14 its serial port. Depending on the modem used, you can pass more or less
  15 parameters to this command,
  16 2- switch the serial line to using the n_gsm line discipline by using
  17 TIOCSETD ioctl,
  18 3- configure the mux using GSMIOC_GETCONF / GSMIOC_SETCONF ioctl,
  19
  20 Major 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
  63 4- create the devices corresponding to the "virtual" serial ports (take care,
  64 each modem has its configuration and some DLC have dedicated functions,
  65 for example GPS), starting with minor 1 (DLC0 is reserved for the management
  66 of the mux)
  67
  68 MAJOR=`cat /proc/devices |grep gsmtty | awk '{print $1}`
  69 for i in `seq 1 4`; do
  70         mknod /dev/ttygsm$i c $MAJOR $i
  71 done
  72
  73 5- use these devices as plain serial ports.
  74 for 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
  78 6- first close all virtual ports before closing the physical port.
  79
  80 Additional Documentation
  81 ------------------------
  82 More practical details on the protocol and how it's supported by industrial
  83 modems can be found in the following documents :
  84 http://www.telit.com/module/infopool/download.php?id=616
  85 http://www.u-blox.com/images/downloads/Product_Docs/LEON-G100-G200-MuxImplementation_ApplicationNote_%28GSM%20G1-CS-10002%29.pdf
  86 http://www.sierrawireless.com/Support/Downloads/AirPrime/WMP_Series/~/media/Support_Downloads/AirPrime/Application_notes/CMUX_Feature_Application_Note-Rev004.ashx
  87 http://wm.sim.com/sim/News/photo/2010721161442.pdf
  88
  89 11-03-08 - Eric Bénard - <eric@eukrea.com>