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Guessing the first tty for a gsm0710 multiplexed serial device is not currently possible, which makes it racy to use with multiple modems. Add a way to map the physical serial tty to its related mux devices using an ioctl. Signed-off-by: Martin Hundebøll <martin@geanix.com> Link: https://lore.kernel.org/r/20190812211243.98686-1-martin@geanix.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
101 lines
3.5 KiB
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101 lines
3.5 KiB
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==============================
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GSM 0710 tty multiplexor HOWTO
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==============================
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This line discipline implements the GSM 07.10 multiplexing protocol
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detailed in the following 3GPP document:
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http://www.3gpp.org/ftp/Specs/archive/07_series/07.10/0710-720.zip
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This document give some hints on how to use this driver with GPRS and 3G
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modems connected to a physical serial port.
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How to use it
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-------------
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1. initialize the modem in 0710 mux mode (usually AT+CMUX= command) through
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its serial port. Depending on the modem used, you can pass more or less
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parameters to this command,
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2. switch the serial line to using the n_gsm line discipline by using
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TIOCSETD ioctl,
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3. configure the mux using GSMIOC_GETCONF / GSMIOC_SETCONF ioctl,
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4. obtain base gsmtty number for the used serial port,
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Major parts of the initialization program :
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(a good starting point is util-linux-ng/sys-utils/ldattach.c)::
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#include <stdio.h>
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#include <stdint.h>
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#include <linux/gsmmux.h>
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#include <linux/tty.h>
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#define DEFAULT_SPEED B115200
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#define SERIAL_PORT /dev/ttyS0
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int ldisc = N_GSM0710;
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struct gsm_config c;
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struct termios configuration;
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uint32_t first;
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/* open the serial port connected to the modem */
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fd = open(SERIAL_PORT, O_RDWR | O_NOCTTY | O_NDELAY);
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/* configure the serial port : speed, flow control ... */
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/* send the AT commands to switch the modem to CMUX mode
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and check that it's successful (should return OK) */
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write(fd, "AT+CMUX=0\r", 10);
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/* experience showed that some modems need some time before
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being able to answer to the first MUX packet so a delay
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may be needed here in some case */
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sleep(3);
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/* use n_gsm line discipline */
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ioctl(fd, TIOCSETD, &ldisc);
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/* get n_gsm configuration */
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ioctl(fd, GSMIOC_GETCONF, &c);
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/* we are initiator and need encoding 0 (basic) */
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c.initiator = 1;
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c.encapsulation = 0;
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/* our modem defaults to a maximum size of 127 bytes */
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c.mru = 127;
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c.mtu = 127;
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/* set the new configuration */
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ioctl(fd, GSMIOC_SETCONF, &c);
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/* get first gsmtty device node */
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ioctl(fd, GSMIOC_GETFIRST, &first);
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printf("first muxed line: /dev/gsmtty%i\n", first);
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/* and wait for ever to keep the line discipline enabled */
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daemon(0,0);
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pause();
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5. use these devices as plain serial ports.
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for example, it's possible:
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- and to use gnokii to send / receive SMS on ttygsm1
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- to use ppp to establish a datalink on ttygsm2
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6. first close all virtual ports before closing the physical port.
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Note that after closing the physical port the modem is still in multiplexing
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mode. This may prevent a successful re-opening of the port later. To avoid
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this situation either reset the modem if your hardware allows that or send
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a disconnect command frame manually before initializing the multiplexing mode
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for the second time. The byte sequence for the disconnect command frame is::
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0xf9, 0x03, 0xef, 0x03, 0xc3, 0x16, 0xf9.
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Additional Documentation
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------------------------
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More practical details on the protocol and how it's supported by industrial
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modems can be found in the following documents :
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- http://www.telit.com/module/infopool/download.php?id=616
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- http://www.u-blox.com/images/downloads/Product_Docs/LEON-G100-G200-MuxImplementation_ApplicationNote_%28GSM%20G1-CS-10002%29.pdf
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- http://www.sierrawireless.com/Support/Downloads/AirPrime/WMP_Series/~/media/Support_Downloads/AirPrime/Application_notes/CMUX_Feature_Application_Note-Rev004.ashx
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- http://wm.sim.com/sim/News/photo/2010721161442.pdf
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11-03-08 - Eric Bénard - <eric@eukrea.com>
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