============================== GSM 0710 tty multiplexor HOWTO ============================== .. contents:: :local: 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 ============= Config Initiator ---------------- #. 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. #. Switch the serial line to using the n_gsm line discipline by using ``TIOCSETD`` ioctl. #. Configure the mux using ``GSMIOC_GETCONF_EXT``/``GSMIOC_SETCONF_EXT`` ioctl if needed. #. Configure the mux using ``GSMIOC_GETCONF``/``GSMIOC_SETCONF`` ioctl. #. Configure DLCs using ``GSMIOC_GETCONF_DLCI``/``GSMIOC_SETCONF_DLCI`` ioctl for non-defaults. #. 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 #include #include #include #define DEFAULT_SPEED B115200 #define SERIAL_PORT /dev/ttyS0 int ldisc = N_GSM0710; struct gsm_config c; struct gsm_config_ext ce; struct gsm_dlci_config dc; 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 extended configuration */ ioctl(fd, GSMIOC_GETCONF_EXT, &ce); /* use keep-alive once every 5s for modem connection supervision */ ce.keep_alive = 500; /* set the new extended configuration */ ioctl(fd, GSMIOC_SETCONF_EXT, &ce); /* 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 DLC 1 configuration */ dc.channel = 1; ioctl(fd, GSMIOC_GETCONF_DLCI, &dc); /* the first user channel gets a higher priority */ dc.priority = 1; /* set the new DLC 1 specific configuration */ ioctl(fd, GSMIOC_SETCONF_DLCI, &dc); /* 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(); #. Use these devices as plain serial ports. For example, it's possible: - to use *gnokii* to send / receive SMS on ``ttygsm1`` - to use *ppp* to establish a datalink on ``ttygsm2`` #. 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 Config Requester ---------------- #. Receive ``AT+CMUX=`` command through its serial port, initialize mux mode config. #. Switch the serial line to using the *n_gsm* line discipline by using ``TIOCSETD`` ioctl. #. Configure the mux using ``GSMIOC_GETCONF_EXT``/``GSMIOC_SETCONF_EXT`` ioctl if needed. #. Configure the mux using ``GSMIOC_GETCONF``/``GSMIOC_SETCONF`` ioctl. #. Configure DLCs using ``GSMIOC_GETCONF_DLCI``/``GSMIOC_SETCONF_DLCI`` ioctl for non-defaults. #. Obtain base gsmtty number for the used serial port:: #include #include #include #include #define DEFAULT_SPEED B115200 #define SERIAL_PORT /dev/ttyS0 int ldisc = N_GSM0710; struct gsm_config c; struct gsm_config_ext ce; struct gsm_dlci_config dc; struct termios configuration; uint32_t first; /* open the serial port */ fd = open(SERIAL_PORT, O_RDWR | O_NOCTTY | O_NDELAY); /* configure the serial port : speed, flow control ... */ /* get serial data and check "AT+CMUX=command" parameter ... */ /* use n_gsm line discipline */ ioctl(fd, TIOCSETD, &ldisc); /* get n_gsm extended configuration */ ioctl(fd, GSMIOC_GETCONF_EXT, &ce); /* use keep-alive once every 5s for peer connection supervision */ ce.keep_alive = 500; /* set the new extended configuration */ ioctl(fd, GSMIOC_SETCONF_EXT, &ce); /* get n_gsm configuration */ ioctl(fd, GSMIOC_GETCONF, &c); /* we are requester and need encoding 0 (basic) */ c.initiator = 0; 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 DLC 1 configuration */ dc.channel = 1; ioctl(fd, GSMIOC_GETCONF_DLCI, &dc); /* the first user channel gets a higher priority */ dc.priority = 1; /* set the new DLC 1 specific configuration */ ioctl(fd, GSMIOC_SETCONF_DLCI, &dc); /* 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(); 11-03-08 - Eric Bénard -