linux 下使用gprs模块通过ppp上网

在开发板上连接gprs模块，使用这个模块上网。(开发板devkit8500,3G模块SIM5320E-EVB-KIT)

1.首先得让内核支持PPP，进入Linux 内核目录（kernel-2.6 或 以上内核版本），执行 #make menuconfig

添加如下内核选项：（这一步一般是不用做的，因为mini2440其实已经添加了此功能了）
Device Drivers ---> Network device support --->

<*> PPP (point-to-point protocol) support

[*]   PPP multilink support

<*> PPP support for async serial ports

<*> PPP support for sync tty ports

<*> SLIP (serial line) support

[*]   CSLIP compressed headers
添加完成后保存并退出，编译出完整的内核文件再烧到开发板中

2.下载ppp-2.4.4.tar.gz 或其他版本PPP 拨号程序源码，可以上网搜索下载
解压文件，进入目录ppp-2.4.4中，执行配置命令
#./configure
再执行
#make CC=/opt/arm-2007q3/bin/arm-none-linux-gnueabi-gcc （后面的CC表示你的交叉编译器目录，要是你添加PATH路径，直接CC=arm-linux-gcc）
有些开发板会有两个交叉编译器，一个是编译内核，驱动等用的编译器，另一个是编译上层应用的，此处应该用编译上层应用的编译器。

3.复制相关文件到开发板
在编译完成之后的ppp中的script 目录复制ppp-on 、ppp-off 到/bin中，将ppp-dial-on 复制到/etc下。
再将pppd目录中的pppd ，chat目录中的chat 两个可执行文件复制到 /bin 中。

4.修改相关拨号脚本
ppp-on脚本为配置gprs提供的usb转串口的接口
=================================================================================================================================
#!/bin/sh
#
# Script to initiate a ppp connection. This is the first part of the
# pair of scripts. This is not a secure pair of scripts as the codes
# are visible with the 'ps' command.  However, it is simple.
#
# These are the parameters. Change as needed.
TELEPHONE=*99#          # The telephone number for the connection
ACCOUNT=3gnet           # The account name for logon (as in 'George Burns')
#PASSWORD=gracie                # The password for this account (and 'Gracie Allen')
LOCAL_IP=0.0.0.0        # Local IP address if known. Dynamic = 0.0.0.0
REMOTE_IP=0.0.0.0       # Remote IP address if desired. Normally 0.0.0.0
NETMASK=255.255.255.0   # The proper netmask if needed
#
# Export them so that they will be available at 'ppp-on-dialer' time.
export TELEPHONE ACCOUNT PASSWORD
#
# This is the location of the script which dials the phone and logs
# in.  Please use the absolute file name as the $PATH variable is not
# used on the connect option.  (To do so on a 'root' account would be
# a security hole so don't ask.)
#
DIALER_SCRIPT=/etc/ppp-on-dialer
#
# Initiate the connection
#
# I put most of the common options on this command. Please, don't
# forget the 'lock' option or some programs such as mgetty will not
# work. The asyncmap and escape will permit the PPP link to work with
# a telnet or rlogin connection. You are welcome to make any changes
# as desired. Don't use the 'defaultroute' option if you currently
# have a default route to an ethernet gateway.
#
exec /bin/pppd debug nodetach lock modem crtscts /dev/ttyUSB2 115200 \
        asyncmap 20A0000 escape FF kdebug 0 $LOCAL_IP:$REMOTE_IP \
        noipdefault netmask $NETMASK defaultroute connect $DIALER_SCRIPT
**********************************************************************************************************************************
其中一些参数的说明：
TELEPHONE、   ACCOUNT、  PASSWORD分别运营商的拨号号码，账号，密码。三大运营商的设置如下
中国联通(WCDMA） 拨号号码：*99#   账号和密码为空
中国电信(CDMA2000)  拨号号码 #777  账号：[e-mail]  密码：vnet.mobi  1x网络的账号和密码为：card（CARD）
中国移动           拨号号码 *98*1#（TD-SCDMA）*99***1#(GSM) 账号和密码为空。

DIALER_SCRIPT=/etc/ppp-on-dialer   实际拨号连接网络的脚本位置。

在执行pppd的一些参数含义：
debug  输出调试信息；
nodetach  不后台运行，默认是后台运行的；
modem  这个参数使得pppd进程将等待模块发回的CD (Carrier  Detect)信号，与local 真好相反；
crtscts  接口带硬件流控 ；
dev/ttyUSB2  接口；
115200  接口波特率；
defaultroute  本地和远端的ip 都设为0使得接入的isp 分配本地的ip 地址；
connect $DIALER_SCRIPT  调用连接chat脚本；  
==================================================================================================================================
ppp-dial-on为实际拨号联网的脚本：
==================================================================================================================================
#!/bin/sh
#
# This is part 2 of the ppp-on script. It will perform the connection
# protocol for the desired connection.
#
exec chat -v                                            \
        TIMEOUT         3                               \
        ABORT           '\nBUSY\r'                      \
        ABORT           '\nNO ANSWER\r'                 \
        ABORT           '\nRINGING\r\n\r\nRINGING\r'    \
        ''              \rAT                            \
        'OK-+++\c-OK'   ATH0                            \
        TIMEOUT         30                              \
        OK              ATDT$TELEPHONE                  \
        CONNECT         ''                              \
#       ogin:--ogin:    $ACCOUNT                        \
#       assword:        $PASSWORD
**********************************************************************************************************************************
联通、移动的可以注释掉最后两行，不输入账号密码，登陆。
TIMEOUT         3  为超时设置，超过3s超时，退出
ABORT        指定了AT指令交互时，出了什么样的错误chat将退出。
AT           指令交互是”接收”“发送”的形式。
比如： ''              \rAT
表示不接收任何信息，直接发送AT
        OK              ATDT$TELEPHONE
表示等待接收OK，如果OK，发送ATD$TELEPHONE   这个命令
==================================================================================================================================
ppp-off 为关闭ppp连接脚本
#!/bin/sh
######################################################################
#
# Determine the device to be terminated.
#
if [ "$1" = "" ]; then
        DEVICE=ppp0
else
        DEVICE=$1
fi

######################################################################
#
# If the ppp0 pid file is present then the program is running. Stop it.
if [ -r /var/run/$DEVICE.pid ]; then
        kill -INT `cat /var/run/$DEVICE.pid`
#
# If the kill did not work then there is no process running for this
# pid. It may also mean that the lock file will be left. You may wish
# to delete the lock file at the same time.
        if [ ! "$?" = "0" ]; then
                rm -f /var/run/$DEVICE.pid
                echo "ERROR: Removed stale pid file"
                exit 1
        fi
#
# Success. Let pppd clean up its own junk.
        echo "PPP link to $DEVICE terminated."
        exit 0
fi
#
# The ppp process is not running for ppp0
echo "ERROR: PPP link is not active on $DEVICE"
exit 1