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1==============================
2GSM 0710 tty multiplexor HOWTO
3==============================
4
5This line discipline implements the GSM 07.10 multiplexing protocol
6detailed in the following 3GPP document:
7
8 https://www.3gpp.org/ftp/Specs/archive/07_series/07.10/0710-720.zip
9
10This document give some hints on how to use this driver with GPRS and 3G
11modems connected to a physical serial port.
12
13How to use it
14-------------
151. config initiator
16^^^^^^^^^^^^^^^^^^^^^
17
181.1 initialize the modem in 0710 mux mode (usually AT+CMUX= command) through
19 its serial port. Depending on the modem used, you can pass more or less
20 parameters to this command.
21
221.2 switch the serial line to using the n_gsm line discipline by using
23 TIOCSETD ioctl.
24
251.3 configure the mux using GSMIOC_GETCONF / GSMIOC_SETCONF ioctl.
26
271.4 obtain base gsmtty number for the used serial port.
28
29Major parts of the initialization program :
30(a good starting point is util-linux-ng/sys-utils/ldattach.c)::
31
32 #include <stdio.h>
33 #include <stdint.h>
34 #include <linux/gsmmux.h>
35 #include <linux/tty.h>
36 #define DEFAULT_SPEED B115200
37 #define SERIAL_PORT /dev/ttyS0
38
39 int ldisc = N_GSM0710;
40 struct gsm_config c;
41 struct termios configuration;
42 uint32_t first;
43
44 /* open the serial port connected to the modem */
45 fd = open(SERIAL_PORT, O_RDWR | O_NOCTTY | O_NDELAY);
46
47 /* configure the serial port : speed, flow control ... */
48
49 /* send the AT commands to switch the modem to CMUX mode
50 and check that it's successful (should return OK) */
51 write(fd, "AT+CMUX=0\r", 10);
52
53 /* experience showed that some modems need some time before
54 being able to answer to the first MUX packet so a delay
55 may be needed here in some case */
56 sleep(3);
57
58 /* use n_gsm line discipline */
59 ioctl(fd, TIOCSETD, &ldisc);
60
61 /* get n_gsm configuration */
62 ioctl(fd, GSMIOC_GETCONF, &c);
63 /* we are initiator and need encoding 0 (basic) */
64 c.initiator = 1;
65 c.encapsulation = 0;
66 /* our modem defaults to a maximum size of 127 bytes */
67 c.mru = 127;
68 c.mtu = 127;
69 /* set the new configuration */
70 ioctl(fd, GSMIOC_SETCONF, &c);
71 /* get first gsmtty device node */
72 ioctl(fd, GSMIOC_GETFIRST, &first);
73 printf("first muxed line: /dev/gsmtty%i\n", first);
74
75 /* and wait for ever to keep the line discipline enabled */
76 daemon(0,0);
77 pause();
78
791.5 use these devices as plain serial ports.
80
81 for example, it's possible:
82
83 - and to use gnokii to send / receive SMS on ttygsm1
84 - to use ppp to establish a datalink on ttygsm2
85
861.6 first close all virtual ports before closing the physical port.
87
88 Note that after closing the physical port the modem is still in multiplexing
89 mode. This may prevent a successful re-opening of the port later. To avoid
90 this situation either reset the modem if your hardware allows that or send
91 a disconnect command frame manually before initializing the multiplexing mode
92 for the second time. The byte sequence for the disconnect command frame is::
93
94 0xf9, 0x03, 0xef, 0x03, 0xc3, 0x16, 0xf9.
95
962. config requester
97^^^^^^^^^^^^^^^^^^^^^
98
992.1 receive string "AT+CMUX= command" through its serial port,initialize
100 mux mode config
101
1022.2 switch the serial line to using the n_gsm line discipline by using
103 TIOCSETD ioctl.
104
1052.3 configure the mux using GSMIOC_GETCONF / GSMIOC_SETCONF ioctl.
106
1072.4 obtain base gsmtty number for the used serial port::
108
109 #include <stdio.h>
110 #include <stdint.h>
111 #include <linux/gsmmux.h>
112 #include <linux/tty.h>
113 #define DEFAULT_SPEED B115200
114 #define SERIAL_PORT /dev/ttyS0
115
116 int ldisc = N_GSM0710;
117 struct gsm_config c;
118 struct termios configuration;
119 uint32_t first;
120
121 /* open the serial port */
122 fd = open(SERIAL_PORT, O_RDWR | O_NOCTTY | O_NDELAY);
123
124 /* configure the serial port : speed, flow control ... */
125
126 /* get serial data and check "AT+CMUX=command" parameter ... */
127
128 /* use n_gsm line discipline */
129 ioctl(fd, TIOCSETD, &ldisc);
130
131 /* get n_gsm configuration */
132 ioctl(fd, GSMIOC_GETCONF, &c);
133 /* we are requester and need encoding 0 (basic) */
134 c.initiator = 0;
135 c.encapsulation = 0;
136 /* our modem defaults to a maximum size of 127 bytes */
137 c.mru = 127;
138 c.mtu = 127;
139 /* set the new configuration */
140 ioctl(fd, GSMIOC_SETCONF, &c);
141 /* get first gsmtty device node */
142 ioctl(fd, GSMIOC_GETFIRST, &first);
143 printf("first muxed line: /dev/gsmtty%i\n", first);
144
145 /* and wait for ever to keep the line discipline enabled */
146 daemon(0,0);
147 pause();
148
149Additional Documentation
150------------------------
151More practical details on the protocol and how it's supported by industrial
152modems can be found in the following documents :
153
154- http://www.telit.com/module/infopool/download.php?id=616
155- http://www.u-blox.com/images/downloads/Product_Docs/LEON-G100-G200-MuxImplementation_ApplicationNote_%28GSM%20G1-CS-10002%29.pdf
156- http://www.sierrawireless.com/Support/Downloads/AirPrime/WMP_Series/~/media/Support_Downloads/AirPrime/Application_notes/CMUX_Feature_Application_Note-Rev004.ashx
157- http://wm.sim.com/sim/News/photo/2010721161442.pdf
158
15911-03-08 - Eric Bénard - <eric@eukrea.com>