Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 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 Note that after closing the physical port the modem is still in multiplexing 81 mode. This may prevent a successful re-opening of the port later. To avoid 82 this situation either reset the modem if your hardware allows that or send 83 a disconnect command frame manually before initializing the multiplexing mode 84 for the second time. The byte sequence for the disconnect command frame is: 85 0xf9, 0x03, 0xef, 0x03, 0xc3, 0x16, 0xf9. 86 87 Additional Documentation 88 ------------------------ 89 More practical details on the protocol and how it's supported by industrial 90 modems can be found in the following documents : 91 http://www.telit.com/module/infopool/download.php?id=616 92 http://www.u-blox.com/images/downloads/Product_Docs/LEON-G100-G200-MuxImplementation_ApplicationNote_%28GSM%20G1-CS-10002%29.pdf 93 http://www.sierrawireless.com/Support/Downloads/AirPrime/WMP_Series/~/media/Support_Downloads/AirPrime/Application_notes/CMUX_Feature_Application_Note-Rev004.ashx 94 http://wm.sim.com/sim/News/photo/2010721161442.pdf 95 96 11-03-08 - Eric Bénard - <eric@eukrea.com>