1==============================
2GSM 0710 tty multiplexor HOWTO
3==============================
4
5.. contents:: :local:
6
7This line discipline implements the GSM 07.10 multiplexing protocol
8detailed in the following 3GPP document:
9
10	https://www.3gpp.org/ftp/Specs/archive/07_series/07.10/0710-720.zip
11
12This document give some hints on how to use this driver with GPRS and 3G
13modems connected to a physical serial port.
14
15How to use it
16=============
17
18Config Initiator
19----------------
20
21#. Initialize the modem in 0710 mux mode (usually ``AT+CMUX=`` command) through
22   its serial port. Depending on the modem used, you can pass more or less
23   parameters to this command.
24
25#. Switch the serial line to using the n_gsm line discipline by using
26   ``TIOCSETD`` ioctl.
27
28#. Configure the mux using ``GSMIOC_GETCONF_EXT``/``GSMIOC_SETCONF_EXT`` ioctl if needed.
29
30#. Configure the mux using ``GSMIOC_GETCONF``/``GSMIOC_SETCONF`` ioctl.
31
32#. Configure DLCs using ``GSMIOC_GETCONF_DLCI``/``GSMIOC_SETCONF_DLCI`` ioctl for non-defaults.
33
34#. Obtain base gsmtty number for the used serial port.
35
36   Major parts of the initialization program
37   (a good starting point is util-linux-ng/sys-utils/ldattach.c)::
38
39      #include <stdio.h>
40      #include <stdint.h>
41      #include <linux/gsmmux.h>
42      #include <linux/tty.h>
43
44      #define DEFAULT_SPEED	B115200
45      #define SERIAL_PORT	/dev/ttyS0
46
47      int ldisc = N_GSM0710;
48      struct gsm_config c;
49      struct gsm_config_ext ce;
50      struct gsm_dlci_config dc;
51      struct termios configuration;
52      uint32_t first;
53
54      /* open the serial port connected to the modem */
55      fd = open(SERIAL_PORT, O_RDWR | O_NOCTTY | O_NDELAY);
56
57      /* configure the serial port : speed, flow control ... */
58
59      /* send the AT commands to switch the modem to CMUX mode
60         and check that it's successful (should return OK) */
61      write(fd, "AT+CMUX=0\r", 10);
62
63      /* experience showed that some modems need some time before
64         being able to answer to the first MUX packet so a delay
65         may be needed here in some case */
66      sleep(3);
67
68      /* use n_gsm line discipline */
69      ioctl(fd, TIOCSETD, &ldisc);
70
71      /* get n_gsm extended configuration */
72      ioctl(fd, GSMIOC_GETCONF_EXT, &ce);
73      /* use keep-alive once every 5s for modem connection supervision */
74      ce.keep_alive = 500;
75      /* set the new extended configuration */
76      ioctl(fd, GSMIOC_SETCONF_EXT, &ce);
77      /* get n_gsm configuration */
78      ioctl(fd, GSMIOC_GETCONF, &c);
79      /* we are initiator and need encoding 0 (basic) */
80      c.initiator = 1;
81      c.encapsulation = 0;
82      /* our modem defaults to a maximum size of 127 bytes */
83      c.mru = 127;
84      c.mtu = 127;
85      /* set the new configuration */
86      ioctl(fd, GSMIOC_SETCONF, &c);
87      /* get DLC 1 configuration */
88      dc.channel = 1;
89      ioctl(fd, GSMIOC_GETCONF_DLCI, &dc);
90      /* the first user channel gets a higher priority */
91      dc.priority = 1;
92      /* set the new DLC 1 specific configuration */
93      ioctl(fd, GSMIOC_SETCONF_DLCI, &dc);
94      /* get first gsmtty device node */
95      ioctl(fd, GSMIOC_GETFIRST, &first);
96      printf("first muxed line: /dev/gsmtty%i\n", first);
97
98      /* and wait for ever to keep the line discipline enabled */
99      daemon(0,0);
100      pause();
101
102#. Use these devices as plain serial ports.
103
104   For example, it's possible:
105
106   - to use *gnokii* to send / receive SMS on ``ttygsm1``
107   - to use *ppp* to establish a datalink on ``ttygsm2``
108
109#. First close all virtual ports before closing the physical port.
110
111   Note that after closing the physical port the modem is still in multiplexing
112   mode. This may prevent a successful re-opening of the port later. To avoid
113   this situation either reset the modem if your hardware allows that or send
114   a disconnect command frame manually before initializing the multiplexing mode
115   for the second time. The byte sequence for the disconnect command frame is::
116
117      0xf9, 0x03, 0xef, 0x03, 0xc3, 0x16, 0xf9
118
119Config Requester
120----------------
121
122#. Receive ``AT+CMUX=`` command through its serial port, initialize mux mode
123   config.
124
125#. Switch the serial line to using the *n_gsm* line discipline by using
126   ``TIOCSETD`` ioctl.
127
128#. Configure the mux using ``GSMIOC_GETCONF_EXT``/``GSMIOC_SETCONF_EXT``
129   ioctl if needed.
130
131#. Configure the mux using ``GSMIOC_GETCONF``/``GSMIOC_SETCONF`` ioctl.
132
133#. Configure DLCs using ``GSMIOC_GETCONF_DLCI``/``GSMIOC_SETCONF_DLCI`` ioctl for non-defaults.
134
135#. Obtain base gsmtty number for the used serial port::
136
137        #include <stdio.h>
138        #include <stdint.h>
139        #include <linux/gsmmux.h>
140        #include <linux/tty.h>
141        #define DEFAULT_SPEED	B115200
142        #define SERIAL_PORT	/dev/ttyS0
143
144	int ldisc = N_GSM0710;
145	struct gsm_config c;
146	struct gsm_config_ext ce;
147	struct gsm_dlci_config dc;
148	struct termios configuration;
149	uint32_t first;
150
151	/* open the serial port */
152	fd = open(SERIAL_PORT, O_RDWR | O_NOCTTY | O_NDELAY);
153
154	/* configure the serial port : speed, flow control ... */
155
156	/* get serial data and check "AT+CMUX=command" parameter ... */
157
158	/* use n_gsm line discipline */
159	ioctl(fd, TIOCSETD, &ldisc);
160
161	/* get n_gsm extended configuration */
162	ioctl(fd, GSMIOC_GETCONF_EXT, &ce);
163	/* use keep-alive once every 5s for peer connection supervision */
164	ce.keep_alive = 500;
165	/* set the new extended configuration */
166	ioctl(fd, GSMIOC_SETCONF_EXT, &ce);
167	/* get n_gsm configuration */
168	ioctl(fd, GSMIOC_GETCONF, &c);
169	/* we are requester and need encoding 0 (basic) */
170	c.initiator = 0;
171	c.encapsulation = 0;
172	/* our modem defaults to a maximum size of 127 bytes */
173	c.mru = 127;
174	c.mtu = 127;
175	/* set the new configuration */
176	ioctl(fd, GSMIOC_SETCONF, &c);
177	/* get DLC 1 configuration */
178	dc.channel = 1;
179	ioctl(fd, GSMIOC_GETCONF_DLCI, &dc);
180	/* the first user channel gets a higher priority */
181	dc.priority = 1;
182	/* set the new DLC 1 specific configuration */
183	ioctl(fd, GSMIOC_SETCONF_DLCI, &dc);
184	/* get first gsmtty device node */
185	ioctl(fd, GSMIOC_GETFIRST, &first);
186	printf("first muxed line: /dev/gsmtty%i\n", first);
187
188	/* and wait for ever to keep the line discipline enabled */
189	daemon(0,0);
190	pause();
191
19211-03-08 - Eric Bénard - <eric@eukrea.com>
193