------------------------------------------------------------------------------------------------------------------------------
交叉编译器：arm-linux-gcc-4.5.4
Linux内核版本：Linux-3.0
主机操作系统：Centos 6.5
开发板：FL2440
GPRS:SIM900A
在开发SIM900模块之前，开发板已经加载了linux内核以及文件系统，并且开发板串口已经使能。并且一定要注意的是：要有一张没有欠费的电话卡！不要笑，这是个很严肃的问题！
------------------------------------------------------------------------------------------------------------------------------
所需源码：
ppp-2.4.4.tar.gz http://download.chinaunix.net/download.php?id=35208&ResourceID=8334
注：个人觉得这是一个比较典型又比较简单的移植问题。
大体步骤：添加内核ppp上网的支持-->编译ppp-2.4.4生成一些可执行文件(pppd, chat, pppdump, pppstats)放到开发板的/usr/sbin/目录下-->将可执行脚本放在开发板的指定位置(/etc/ppp/peers/gprs, /etc/ppp/chat-gprs-connect)，并执行pppd命令。
一、添加内核支持
Linux-3.0以上的版本中，rt3070的驱动已经加入了内核源码中去了，本篇用的是Linux-3.0的内核，只需要在内核的make menuconfig中选择ppp上网的支持就可以了。
修改如下：
Device Drivers --->
[*] Network device support --->
<*> PPP (point-to-point protocol) support
[*] PPP multilink support (EXPERIMENTAL)
<*> PPP support for async serial ports
<*> PPP support for sync tty ports
<*> SLIP (serial line) support
[*] CSLIP compressed headers
二、编译ppp-2.4.4
# tar -xzf ppp-2.4.4.tar.gz
# ./configure
# make CC=/opt/buildroot-2012.08/arm920t/usr/bin/arm-linux-gcc (交叉编译器)
如果编译成功，则会在pppd, chat, pppdump, pppstats下分别生成可执行程序pppd, chat, pppdump, pppstats。将其拷贝到开发板的/usr/sbin目录下。
三、开发板的配置
# vi /etc/ppp/peers/gprs
# Usage: root>pppd call gprs #set seriral
/dev/ttyS1 # set baudrate # set flowdate
nocrtscts connect '/usr/sbin/chat -v -f /etc/ppp/gprs-connect-chat' #set debug ,send message to /var/log/messages
debug #To keep pppd on the terminal
nodetach #hide-password # Accept the peer's idea of our local IP address
ipcp-accept-local
# Accept the peer's idea of its (remote) IP address
ipcp-accept-remote #dial up connetion as the default route
defaultroute usepeerdns
# vi /etc/ppp/chat-gprs-connect
#Copyright (c) guanlei @qq.com
# This is second part of the ppp dial script. It will perform the connection
#
ABORT 'BUSY'
ABORT 'NO ANSWER'
ABORT 'NO CARRIER'
ABORT 'NO DIALTONE'
ABORT 'ERROR'
ABORT '\nRING\r\n\r\nRING\r'
TIMEOUT
'' \rAT
#set apn
OK AT+CGDCONT=,"IP","cmnet"
# ............
OK ATDT****# //这里要改成相应的运行商的设置
SAY " + requesting data connection\n"
CONNECT ''
SAY " + connected\n"
使能pppd:
# pppd call gprs & (&表示后台运行)
配置完就可以了，现在可以测试一下上网功能了：
# ping www.baidu.com
PING www.baidu.com (103.235.46.39): 56 data bytes
64 bytes from 103.235.46.39: seq=0 ttl=48 time=555.719 ms
64 bytes from 103.235.46.39: seq=1 ttl=48 time=273.481 ms
--- www.baidu.com ping statistics ---
3 packets transmitted, 2 packets received, 33% packet loss
round-trip min/avg/max = 273.481/414.600/555.719 ms
# ifconfig
ppp0 Link encap:Point-to-Point Protocol
inet addr:10.110.1.110 P-t-P:192.200.1.21 Mask:255.255.255.255
UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1500 Metric:1
RX packets:10 errors:0 dropped:0 overruns:0 frame:0
TX packets:12 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:3
RX bytes:686 (686.0 B) TX bytes:557 (557.0 B)