| n_gsm.c GSM 0710 tty multiplexor HOWTO |
| =================================================== |
| |
| This line discipline implements the GSM 07.10 multiplexing protocol |
| detailed in the following 3GPP document : |
| http://www.3gpp.org/ftp/Specs/archive/07_series/07.10/0710-720.zip |
| |
| This document give some hints on how to use this driver with GPRS and 3G |
| modems connected to a physical serial port. |
| |
| How to use it |
| ------------- |
| 1- initialize the modem in 0710 mux mode (usually AT+CMUX= command) through |
| its serial port. Depending on the modem used, you can pass more or less |
| parameters to this command, |
| 2- switch the serial line to using the n_gsm line discipline by using |
| TIOCSETD ioctl, |
| 3- configure the mux using GSMIOC_GETCONF / GSMIOC_SETCONF ioctl, |
| |
| Major parts of the initialization program : |
| (a good starting point is util-linux-ng/sys-utils/ldattach.c) |
| #include <linux/gsmmux.h> |
| #define N_GSM0710 21 /* GSM 0710 Mux */ |
| #define DEFAULT_SPEED B115200 |
| #define SERIAL_PORT /dev/ttyS0 |
| |
| int ldisc = N_GSM0710; |
| struct gsm_config c; |
| struct termios configuration; |
| |
| /* open the serial port connected to the modem */ |
| fd = open(SERIAL_PORT, O_RDWR | O_NOCTTY | O_NDELAY); |
| |
| /* configure the serial port : speed, flow control ... */ |
| |
| /* send the AT commands to switch the modem to CMUX mode |
| and check that it's succesful (should return OK) */ |
| write(fd, "AT+CMUX=0\r", 10); |
| |
| /* experience showed that some modems need some time before |
| being able to answer to the first MUX packet so a delay |
| may be needed here in some case */ |
| sleep(3); |
| |
| /* use n_gsm line discipline */ |
| ioctl(fd, TIOCSETD, &ldisc); |
| |
| /* get n_gsm configuration */ |
| ioctl(fd, GSMIOC_GETCONF, &c); |
| /* we are initiator and need encoding 0 (basic) */ |
| c.initiator = 1; |
| c.encapsulation = 0; |
| /* our modem defaults to a maximum size of 127 bytes */ |
| c.mru = 127; |
| c.mtu = 127; |
| /* set the new configuration */ |
| ioctl(fd, GSMIOC_SETCONF, &c); |
| |
| /* and wait for ever to keep the line discipline enabled */ |
| daemon(0,0); |
| pause(); |
| |
| 4- create the devices corresponding to the "virtual" serial ports (take care, |
| each modem has its configuration and some DLC have dedicated functions, |
| for example GPS), starting with minor 1 (DLC0 is reserved for the management |
| of the mux) |
| |
| MAJOR=`cat /proc/devices |grep gsmtty | awk '{print $1}` |
| for i in `seq 1 4`; do |
| mknod /dev/ttygsm$i c $MAJOR $i |
| done |
| |
| 5- use these devices as plain serial ports. |
| for example, it's possible : |
| - and to use gnokii to send / receive SMS on ttygsm1 |
| - to use ppp to establish a datalink on ttygsm2 |
| |
| 6- first close all virtual ports before closing the physical port. |
| |
| Additional Documentation |
| ------------------------ |
| More practical details on the protocol and how it's supported by industrial |
| modems can be found in the following documents : |
| http://www.telit.com/module/infopool/download.php?id=616 |
| http://www.u-blox.com/images/downloads/Product_Docs/LEON-G100-G200-MuxImplementation_ApplicationNote_%28GSM%20G1-CS-10002%29.pdf |
| http://www.sierrawireless.com/Support/Downloads/AirPrime/WMP_Series/~/media/Support_Downloads/AirPrime/Application_notes/CMUX_Feature_Application_Note-Rev004.ashx |
| http://wm.sim.com/sim/News/photo/2010721161442.pdf |
| |
| 11-03-08 - Eric Bénard - <eric@eukrea.com> |