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Based on kernel version 3.15.4. Page generated on 2014-07-07 09:04 EST.

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>
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