n_gsm.rst (4698B)
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``/``GSMIOC_SETCONF`` ioctl. 29 30#. Obtain base gsmtty number for the used serial port. 31 32 Major parts of the initialization program 33 (a good starting point is util-linux-ng/sys-utils/ldattach.c):: 34 35 #include <stdio.h> 36 #include <stdint.h> 37 #include <linux/gsmmux.h> 38 #include <linux/tty.h> 39 40 #define DEFAULT_SPEED B115200 41 #define SERIAL_PORT /dev/ttyS0 42 43 int ldisc = N_GSM0710; 44 struct gsm_config c; 45 struct termios configuration; 46 uint32_t first; 47 48 /* open the serial port connected to the modem */ 49 fd = open(SERIAL_PORT, O_RDWR | O_NOCTTY | O_NDELAY); 50 51 /* configure the serial port : speed, flow control ... */ 52 53 /* send the AT commands to switch the modem to CMUX mode 54 and check that it's successful (should return OK) */ 55 write(fd, "AT+CMUX=0\r", 10); 56 57 /* experience showed that some modems need some time before 58 being able to answer to the first MUX packet so a delay 59 may be needed here in some case */ 60 sleep(3); 61 62 /* use n_gsm line discipline */ 63 ioctl(fd, TIOCSETD, &ldisc); 64 65 /* get n_gsm configuration */ 66 ioctl(fd, GSMIOC_GETCONF, &c); 67 /* we are initiator and need encoding 0 (basic) */ 68 c.initiator = 1; 69 c.encapsulation = 0; 70 /* our modem defaults to a maximum size of 127 bytes */ 71 c.mru = 127; 72 c.mtu = 127; 73 /* set the new configuration */ 74 ioctl(fd, GSMIOC_SETCONF, &c); 75 /* get first gsmtty device node */ 76 ioctl(fd, GSMIOC_GETFIRST, &first); 77 printf("first muxed line: /dev/gsmtty%i\n", first); 78 79 /* and wait for ever to keep the line discipline enabled */ 80 daemon(0,0); 81 pause(); 82 83#. Use these devices as plain serial ports. 84 85 For example, it's possible: 86 87 - to use *gnokii* to send / receive SMS on ``ttygsm1`` 88 - to use *ppp* to establish a datalink on ``ttygsm2`` 89 90#. First close all virtual ports before closing the physical port. 91 92 Note that after closing the physical port the modem is still in multiplexing 93 mode. This may prevent a successful re-opening of the port later. To avoid 94 this situation either reset the modem if your hardware allows that or send 95 a disconnect command frame manually before initializing the multiplexing mode 96 for the second time. The byte sequence for the disconnect command frame is:: 97 98 0xf9, 0x03, 0xef, 0x03, 0xc3, 0x16, 0xf9 99 100Config Requester 101---------------- 102 103#. Receive ``AT+CMUX=`` command through its serial port, initialize mux mode 104 config. 105 106#. Switch the serial line to using the *n_gsm* line discipline by using 107 ``TIOCSETD`` ioctl. 108 109#. Configure the mux using ``GSMIOC_GETCONF``/``GSMIOC_SETCONF`` ioctl. 110 111#. Obtain base gsmtty number for the used serial port:: 112 113 #include <stdio.h> 114 #include <stdint.h> 115 #include <linux/gsmmux.h> 116 #include <linux/tty.h> 117 #define DEFAULT_SPEED B115200 118 #define SERIAL_PORT /dev/ttyS0 119 120 int ldisc = N_GSM0710; 121 struct gsm_config c; 122 struct termios configuration; 123 uint32_t first; 124 125 /* open the serial port */ 126 fd = open(SERIAL_PORT, O_RDWR | O_NOCTTY | O_NDELAY); 127 128 /* configure the serial port : speed, flow control ... */ 129 130 /* get serial data and check "AT+CMUX=command" parameter ... */ 131 132 /* use n_gsm line discipline */ 133 ioctl(fd, TIOCSETD, &ldisc); 134 135 /* get n_gsm configuration */ 136 ioctl(fd, GSMIOC_GETCONF, &c); 137 /* we are requester and need encoding 0 (basic) */ 138 c.initiator = 0; 139 c.encapsulation = 0; 140 /* our modem defaults to a maximum size of 127 bytes */ 141 c.mru = 127; 142 c.mtu = 127; 143 /* set the new configuration */ 144 ioctl(fd, GSMIOC_SETCONF, &c); 145 /* get first gsmtty device node */ 146 ioctl(fd, GSMIOC_GETFIRST, &first); 147 printf("first muxed line: /dev/gsmtty%i\n", first); 148 149 /* and wait for ever to keep the line discipline enabled */ 150 daemon(0,0); 151 pause(); 152 15311-03-08 - Eric Bénard - <eric@eukrea.com>