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 Bénard - <eric@eukrea.com>
90