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diff --git a/Documentation/driver-api/serial/n_gsm.rst b/Documentation/driver-api/serial/n_gsm.rst new file mode 100644 index 000000000..87dfcd54a --- /dev/null +++ b/Documentation/driver-api/serial/n_gsm.rst @@ -0,0 +1,100 @@ +============================== +GSM 0710 tty multiplexor HOWTO +============================== + +This line discipline implements the GSM 07.10 multiplexing protocol +detailed in the following 3GPP document: + + https://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, +4. obtain base gsmtty number for the used serial port, + +Major parts of the initialization program : +(a good starting point is util-linux-ng/sys-utils/ldattach.c):: + + #include <stdio.h> + #include <stdint.h> + #include <linux/gsmmux.h> + #include <linux/tty.h> + #define DEFAULT_SPEED B115200 + #define SERIAL_PORT /dev/ttyS0 + + int ldisc = N_GSM0710; + struct gsm_config c; + struct termios configuration; + uint32_t first; + + /* 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 successful (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); + /* get first gsmtty device node */ + ioctl(fd, GSMIOC_GETFIRST, &first); + printf("first muxed line: /dev/gsmtty%i\n", first); + + /* and wait for ever to keep the line discipline enabled */ + daemon(0,0); + pause(); + +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. + + Note that after closing the physical port the modem is still in multiplexing + mode. This may prevent a successful re-opening of the port later. To avoid + this situation either reset the modem if your hardware allows that or send + a disconnect command frame manually before initializing the multiplexing mode + for the second time. The byte sequence for the disconnect command frame is:: + + 0xf9, 0x03, 0xef, 0x03, 0xc3, 0x16, 0xf9. + +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> |