<pre><span style="font-weight: 700;"><span style="font-family: 宋体; font-size: 22pt;">1.</span></span><b style="color: inherit; font-family: inherit;"><span style="font-family: 宋体; font-size: 22pt;"><font face="宋体">启动</font>CMUX<font face="宋体">模式</font></span></b></pre><p class="MsoNormal"><span style="font-family: 宋体; color: rgb(77, 77, 77); font-size: 11pt; background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial;"><font face="宋体">通常模块发送</font>AT＋CMUX命令来激活多路复用，该命令格式为：</span><span style="font-family: 宋体; color: rgb(77, 77, 77); font-size: 11pt; background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial;"><o:p></o:p></span></p><table class="MsoNormalTable" border="1" cellspacing="0" style="width: 489.05pt; margin-left: 5.4pt; border: none;"><tbody><tr><td width="94" valign="top" style="width:56.7000pt;padding:0.0000pt 5.4000pt 0.0000pt 5.4000pt ;border-left:1.0000pt solid rgb(178,161,199);

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命令类型<o:p>

语法<o:p>

返回<o:p>

设置命令<o:p>

AT+CMUX= [[,[,[,[,[,[,[,[,]]]]]]]]]<o:p>

<o:p> 

OK<o:p>

查询命令<o:p>

AT+CMUX?<o:p>

+CMUX:[[,[,[,[,[,[,[,[,]]]]]]]]]<o:p>

<o:p> 

OK<o:p>

测试命令<o:p>

AT+CMUX=?<o:p>

+CMUX:(),(s),( s),(s),(s),(s),(s),(s),(s)  <o:p>

<o:p> 

OK<o:p>

参数定义：<o:p>

2.CMUX 帧结构 

多路复用有三种操作模式：基本模式、带错误恢复功能的高级模式、不带错误恢复功能的高级模式（具体可以参见GSM 07.10协议）。不同的GPRS模块也支持不同的模式。<o:p>

<o:p> 

其中，帧类型可分控制帧和信息帧。 <o:p>

CMUX双方通过控制帧协商用以构建、拆除虚拟链路，控制帧又为以下几种： <o:p>

SABM：建立DLC <o:p>

UA：响应SABM帧或DISC帧 <o:p>

DM：链路未成功建立时，对收到的DISC命令的响应 <o:p>

DISC：通知对端拆除链接，在DLC0发送DISC帧，等于退出MUX功能<o:p>

<o:p> 

信息帧： <o:p>

UIH\UI\I：这三种是信息帧，也就是携带要传输数据的帧。

3.LINUX下的CMUX使用

3.1 挂载USB设备<o:p>

在可移动设备，勾选QinHeng USB2.0-Serial

<o:p>

然后打开终端控制台，ls /dev/ttyUSB*查看USB设备，如下表示挂载成功。

<o:p>

<o:p>

3.2 CMUX虚拟串口生成<o:p>

参考用例：https://www.kernel.org/doc/html/latest/driver-api/serial/n_gsm.html

<o:p>

3.2.1 测试实例gsmmux.h源代码

#ifndef _LINUX_GSMMUX_H
#define _LINUX_GSMMUX_H
 
struct gsm_config
{
unsigned int adaption;
unsigned int encapsulation;
unsigned int initiator;
unsigned int t1;
unsigned int t2;
unsigned int t3;
unsigned int n2;
unsigned int mru;
unsigned int mtu;
unsigned int k;
unsigned int i;
unsigned int unused[8];    /* Padding for expansion without
   breaking stuff /
};
 
#define GSMIOC_GETCONF    _IOR('G', 0, struct gsm_config)
#define GSMIOC_SETCONF    _IOW('G', 1, struct gsm_config)
 
struct gsm_netconfig {
unsigned int adaption;  / Adaption to use in network mode /
unsigned short protocol;/ Protocol to use - only ETH_P_IP supported /
unsigned short unused2;
char if_name[IFNAMSIZ];    / interface name format string /
__u8 unused[28];        / For future use /
};
 
#define GSMIOC_ENABLE_NET      _IOW('G', 2, struct gsm_netconfig)
#define GSMIOC_DISABLE_NET     _IO('G', 3)
 
 
#endif

3.2.2 测试实例cmux.c 源代码

#include <stdlib.h>
#include <stdio.h>
#include <stdarg.h>
#include <string.h>
#include <sys/ioctl.h>
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
/**
    gsmmux.h provides n_gsm line dicipline structures and functions.
    It should be kept in sync with your kernel release.
/
#include "gsmmux.h"
 
/* n_gsm ioctl /
#ifndef N_GSM0710
# define N_GSM0710    21
#endif
 
/ attach a line discipline ioctl /
#ifndef TIOCSETD
# define TIOCSETD    0x5423
#endif
 
/ serial port of the modem /
//#define SERIAL_PORT    "/dev/ttyUSB0"
 
/ line speed /
#define LINE_SPEED    B115200
 
/ maximum transfert unit (MTU), value in bytes /
#define MTU    512
 
/**
 whether or not to create virtual TTYs for the multiplex
    0 : do not create
    1 : create
/
#define CREATE_NODES    1
 
/ number of virtual TTYs to create (most modems can handle up to 4) /
#define NUM_NODES    4
 
/ name of the virtual TTYs to create /
#define BASENAME_NODES    "/dev/ttyGSM"
 
/ name of the driver, used to get the major number /
#define DRIVER_NAME    "gsmtty"
 
/**
 whether or not to print debug messages to stderr
    0 : debug off
    1 : debug on
/
#define DEBUG    1
 
/**
 whether or not to detach the program from the terminal
    0 : do not daemonize
    1 : daemonize
/
#define DAEMONIZE    1
 
 / size of the reception buffer which gets data from the serial line /
#define SIZE_BUF    256
 
 
/**
    Prints debug messages to stderr if debug is wanted
/
static void dbg(char fmt, ...) {
va_list args;
 
if (DEBUG) {
fflush(NULL);
va_start(args, fmt);
vfprintf(stderr, fmt, args);
va_end(args);
fprintf(stderr, "\n");
fflush(NULL);
}
return;
}
 
/
    Sends an AT command to the specified line and gets its result
    Returns  0 on success
    -1 on failure
/
int send_at_command(int serial_fd, char command, int max_retry) {
char buf[SIZE_BUF];
int r;
int retry = 0;
 
do{
/ write the AT command to the serial line /
if (write(serial_fd, command, strlen(command)) <= 0)
err(EXIT_FAILURE, "Cannot write to ttyUSB");
/ wait a bit to allow the modem to rest /
sleep(1);
 
/ read the result of the command from the modem /
memset(buf, 0, sizeof(buf));
r = read(serial_fd, buf, sizeof(buf));
if (r == -1)
{
dbg("read errno %d", errno);
retry++;
dbg("retry write time: %d", retry);
}
/ if there is no result from the modem, return failure /
if (r == 0) {
dbg("%s\t: No response", command);
retry++;
//return -1;
}
if(retry!= 0 && retry >= max_retry)
{
err(EXIT_FAILURE, "Cannot read ttyUSB");
}
else
{
break;
}
}while(1);
 
 
 
/ if we have a result and want debug info, strip CR & LF out from the output /
if (DEBUG) {
int i;
char bufp[SIZE_BUF];
memcpy(bufp, buf, sizeof(buf));
for(i=0; i
if (bufp[i] == '\r' || bufp[i] == '\n')
bufp[i] = ' ';
}
dbg("%s\t: %s", command, bufp);
}
 
/ if the output shows "OK" return success /
if (strstr(buf, "OK\r") != NULL) {
return 0;
}
return -1;    
 
}
 
 
/**
    Gets the major number of the driver device
    Returns  the major number on success
    -1 on failure
/
int get_major(char driver) {
 
FILE *fp;
char *line = NULL;
size_t len = 0;
ssize_t read;
char device[20];
int major = -1;
/ open /proc/devices file /
if ((fp = fopen("/proc/devices", "r")) == NULL)
err(EXIT_FAILURE, "Cannot open /proc/devices");
 
/ read the file line by line /
while ((major == -1) && (read = getline(&line, &len, fp)) != -1) {
/ if the driver name string is found in the line, try to get the major /
if (strstr(line, driver) != NULL) {
if (sscanf(line,"%d %s\n", &major, device) != 2)
major = -1;
}
/ free the line before getting a new one /
if (line) {
free(line);
line = NULL;
}
 
}
 
/ close /proc/devices file /
fclose(fp);
 
return major;
}
 
/
    Creates nodes for the virtual TTYs
    Returns the number of nodes created
/
int make_nodes(int major, char basename, int number_nodes) {
 
int minor, created = 0;
dev_t device;
char node_name[15];
mode_t oldmask;
 
/ set a new mask to get 666 mode and stores the old one /
oldmask = umask(0);
 
for (minor=1; minor
 
/ append the minor number to the base name /
sprintf(node_name, "%s%d", basename, minor);
/ store a device info with major and minor /
device = makedev(major, minor);
/ create the actual character node /
if (mknod(node_name, S_IFCHR | 0666, device) != 0) {
warn("Cannot create %s", node_name);
} else {
created++;
dbg("Created %s", node_name);
}
 
}
 
/ revert the mask to the old one /
umask(oldmask);
 
return created;
}
 
/
    Removes previously created TTY nodes
    Returns nothing, it doesn't really matter if it fails
/
void remove_nodes(char basename, int number_nodes) {
 
int node;
char node_name[15];
 
for (node=1; node
 
/ append the minor number to the base name /
sprintf(node_name, "%s%d", basename, node);
/ unlink the actual character node /
dbg("Removing %s", node_name);
if (unlink(node_name) == -1)
warn("Cannot remove %s", node_name);
 
}
 
return;
}
 
/
    Function raised by signal catching
/
void signal_callback_handler(int signum) {
remove_nodes(BASENAME_NODES, NUM_NODES);
return;
}
int main(int argc, char** argv) {
 
int serial_fd, major;
struct termios tio;
int ldisc = N_GSM0710;
struct gsm_config gsm;
char atcommand[40];
 
char* port;
 
if(argc != 2)
{
printf("usage\n ./cmux /dev/ttyUSBx\n");
exit(-1);
}
port = argv[1];
 
/* print global parameters /
dbg("SERIAL_PORT = %s", port);
 
/ open the serial port /
serial_fd = open(port, O_RDWR | O_NOCTTY | O_NDELAY);
if (serial_fd == -1)
{
dbg("openport ret = %d\n", errno);
err(EXIT_FAILURE, "Cannot open %s", port);
}
/ get the current attributes of the serial port /
if (tcgetattr(serial_fd, &tio) == -1)
err(EXIT_FAILURE, "Cannot get line attributes");
/ set the new attrbiutes */
tio.c_iflag = 0;
tio.c_oflag = 0;
tio.c_cflag = CS8 | CREAD | CLOCAL;
tio.c_cflag &= (CRTSCTS);<o:p>
tio.c_lflag = 0;<o:p>
tio.c_cc[VMIN] = 1;<o:p>
tio.c_cc[VTIME] = 0;<o:p>
<o:p>
/* write the speed of the serial line /<o:p>
if (cfsetospeed(&tio, LINE_SPEED) < 0 || cfsetispeed(&tio, LINE_SPEED) < 0)<o:p>
err(EXIT_FAILURE, “Cannot set line speed”);<o:p>
<o:p>
/ write the attributes /<o:p>
if (tcsetattr(serial_fd, TCSANOW, &tio) == -1)<o:p>
err(EXIT_FAILURE, “Cannot set line attributes”);<o:p>
<o:p> 
/**<o:p>
    Send AT commands to put the modem in CMUX mode.<o:p>
    This is vendor specific and should be changed<o:p>
    to fit your modem needs.<o:p>
    The following matches Quectel M95.<o:p>
/<o:p>
//if (send_at_command(serial_fd, “AT+IFC=2,2\r”) == -1)<o:p>
//    errx(EXIT_FAILURE, “AT+IFC=2,2: bad response”);<o:p>
if (send_at_command(serial_fd, “AT+CGMM\r”, 3) == -1)<o:p>
warnx(“AT+GMM: bad response”);<o:p>
if (send_at_command(serial_fd, “AT\r”, 0) == -1)<o:p>
warnx(“AT: bad response”);<o:p>
sprintf(atcommand, “AT+CMUX=0,0,5\r”);<o:p>
if (send_at_command(serial_fd, atcommand, 0) == -1)<o:p>
errx(EXIT_FAILURE, “Cannot enable modem CMUX”);<o:p>
<o:p> 
/* use n_gsm line discipline /<o:p>
sleep(2);<o:p>
if (ioctl(serial_fd, TIOCSETD, &ldisc) < 0)<o:p>
err(EXIT_FAILURE, “Cannot set line dicipline. Is ‘n_gsm’ module registred?”);<o:p>
<o:p> 
/ get n_gsm configuration /<o:p>
if (ioctl(serial_fd, GSMIOC_GETCONF, &gsm) < 0)<o:p>
err(EXIT_FAILURE, “Cannot get GSM multiplex parameters”);<o:p>
<o:p> 
/ set and write new attributes /<o:p>
gsm.initiator = 1;<o:p>
gsm.encapsulation = 0;<o:p>
gsm.mru = MTU;<o:p>
gsm.mtu = MTU;<o:p>
gsm.t1 = 10;<o:p>
gsm.n2 = 3;<o:p>
gsm.t2 = 30;<o:p>
gsm.t3 = 10;<o:p>
<o:p> 
if (ioctl(serial_fd, GSMIOC_SETCONF, &gsm) < 0)<o:p>
err(EXIT_FAILURE, “Cannot set GSM multiplex parameters”);<o:p>
dbg(“Line dicipline set”);<o:p>
<o:p>
/ create the virtual TTYs /<o:p>
if (CREATE_NODES) {<o:p>
int created;<o:p>
if ((major = get_major(DRIVER_NAME)) < 0)<o:p>
errx(EXIT_FAILURE, “Cannot get major number”);<o:p>
if ((created = make_nodes(major, BASENAME_NODES, NUM_NODES)) < NUM_NODES)<o:p>
warnx(“Cannot create all nodes, only %d/%d have been created.”, created, NUM_NODES);<o:p>
}<o:p>
<o:p> 
/ wait to keep the line discipline enabled, wake it up with a signal /<o:p>
signal(SIGINT, signal_callback_handler);<o:p>
signal(SIGTERM, signal_callback_handler);<o:p>
<o:p>
/ detach from the terminal if needed /<o:p>
if (DAEMONIZE) {<o:p>
dbg(“Going to background”);<o:p>
if (daemon(0,0) != 0)<o:p>
err(EXIT_FAILURE, “Cannot daemonize”);<o:p>
}<o:p>
<o:p> 
dbg(“catching sig”);<o:p>
<o:p> 
pause();<o:p>
<o:p>
/ remove the created virtual TTYs /<o:p>
if (CREATE_NODES) {<o:p>
remove_nodes(BASENAME_NODES, NUM_NODES);<o:p>
}<o:p>
<o:p> 
/ close the serial line */<o:p>
close(serial_fd);<o:p>
<o:p> 
return EXIT_SUCCESS;<o:p>
}

<o:p>

<o:p>

3.2.3 生成cmux可执行文件

通执行gcc cmux.c -o cmux 把cmux.c编译成可执行文件

<o:p>

3.2.4 虚拟串口生成

通执行 ./cmux /dev/ttyUSB0 就会创建几个虚拟串口

<o:p>

下图中的ttyGSM1,ttyGSM2,ttyGSM3,ttyGSM4及为虚拟出的串口

<o:p>

4.2 VMware无法识别USB设备的解决方法

我的虚拟机上认不到USB设备，发现是VMware USB Arbitration Service服务没有启动，手动启动VMware USB Arbitration Service服务，再重启VMware，虚拟机就能识别出USB设备了。<o:p>

具体步骤：
1.点击开始->运行，在对话框中输入”services.msc”，确定，打开windows服务管理器。<o:p>

2.在服务列表中选中”VMware USB Arbitration Service”，双击打开属性对话框，再选择”启动”，就能启动VMware USB Arbitration Service服务了。<o:p>

3.关闭VMware软件，并重新打开，启动一下虚拟机。

4.3 虚拟串口生成失败

如下图所示

<o:p>

出现原因是没有选择正确的USB口，我们720SL开发板上的开关要拨到UART2一端，出现上面的错误的原因是因为开关要拨到UART1一端了，把开关拨到UART2一端，重启一下模块，然后在做上述操作。<o:p>

<o:p>

<o:p>