serialoverip功能与ser2net相似，都能实现IP端口与串口间的数据转发，但不同点在于：
1. 官方发布的ser2net只支持TCP协议转发，增加UDP需要额外加补丁（详见：http://sourceforge.net/p/ser2net/patches/12/）。
2. serialoverip支持且只支持UDP协议转发，但也因此使得其程序非常小巧。后有我注释、替换变量名后的源代码，对此类软件的原理分析很有帮助。
在安装serialoverip后，尝试加入其启动命令到rc.local中，但发现开机并未成功启动serialoverip。几番分析，是由于执行rc.local中语句时OpenWrt的IP分配还未完成（即serialoverip无法绑定192.168.1.1端口），造成启动失败。
由于serialoverip源代码对此情况没有做考虑，所以笔者决定使用sleep来固定等待，修改了rc.local中命令：
sleep 10s && serialoverip -s 192.168.1.1 10002 -d /dev/ttyATH0 9600-8N1 &
先等待10秒再打开192.168.1.1:10002上UDP端口与/dev/ttyATH0串口的转发（加&让其后台运行）。
上例方法基本解决了serialoverip无法启动的问题，但是灵活性还是较低。苦苦搜索了sh命令规范后，本吊探索出一个更灵活的脚本（由于Linux虚拟机没装输入法，所以用英文注解了）：
# Start data forwarding between UDP and Serial.
# If an instance is already running, then exit.
# The starting timeout is 30s.
timeout=30
while [ $timeout -ne 0 ]
do
if [ `ps | grep serialoverip | wc -l` -eq 2 ]
then
break
fi
if [ `ifconfig br-lan | grep 192.168.1.1 | wc -l` -eq 1 ]
then
serialoverip -s 192.168.1.1 10002 -d /dev/ttyATH0 9600-8N1 &
break
fi
let timeout=timeout-1
sleep 1s
done
以上代码功能，检测是否已经完成IP分配，一旦完成分配则启动serialoverip并退出，否则每隔1秒再检测，直到30秒时间全部走完（当然你也可以改个更高的timeout初始值，不过我觉得30秒够长了）。
加到rc.local的exit 0之前就行。当然为了提高rc.local的可读性，还可以将以上代码连同exit 0写入到新的文件（比如udp2serial），放在/etc目录（或其他目录），之后在rc.local的exit 0前加入：
sh /etc/udp2serial
即当执行rc.local时会再去执行/etc下的udp2serial。由于这种方法最坏情况下会造成阻塞，故建议是放在exit 0之前，保证其他命令都执行后再处理（上面的例子均是放在exit 0前）。
以下是我使用的方案
/etc/rc.local文件末尾：
sh /etc/udp2serial exit 0
/etc/udp2serial文件：
# Start data forwarding between UDP and Serial.
# If an instance is already running, then exit.
# The starting timeout is 30s.
timeout=30
while [ $timeout -ne 0 ]
do
if [ `ps | grep serialoverip | wc -l` -eq 2 ]
then
break
fi
if [ `ifconfig br-lan | grep 192.168.1.1 | wc -l` -eq 1 ]
then
serialoverip -s 192.168.1.1 10002 -d /dev/ttyATH0 9600-8N1 &
break
fi
let timeout=timeout-1
sleep 1s
done
exit 0
欢迎跟我讨论更加有效的解决方法：）
我的邮箱：imjgz@qq.com
可以从http://sourceforge.net/projects/serialoverip/获取源代码。
这是serialoverip的源代码，我进行了变量替换和部分的注释（由于Linux虚拟机没装输入法，所以用英文注解了）：
/*
* —————————————————————————-
* serialoverip
* Utility for transport of serial interfaces over UDP/IP
* Copyright (C) 2002 Stefan-Florin Nicola <sten@fx.ro>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place – Suite 330, Boston, MA 02111-1307, USA
*
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <fcntl.h>
#include <termios.h>
#include <signal.h>
#define MAXMESG 2048
char *programName;
int source[2], sourceType[2];
// Display the help.
void PrintHelp()
{
fprintf(stderr,"\
SerialOverIP version 1.0, Copyright (C) 2002 Stefan-Florin Nicola <sten@fx.ro>
SerialOverIP comes with ABSOLUTELY NO WARRANTY. This is free software, and you
are welcome to redistribute it under GNU General Public License.
Usage: %s <source1> <source2>
where <source1> and <source2> are one of the folowing:
-s <IP> <port> UDP server on IP:port
-c <IP> <port> UDP client for server IP:port
-d <device> sss-dps local serial device
sss is speed (50,..,230400)
d is data bits (5,6,7,8)
p is parity type (N,E,O)
s is stop bits (1,2)
",programName);
return;
}
// Set the serial terminal and return the result.
int SetSerial(int source, struct termios *cfg, int baudRate, int dataBits, unsigned char parityType, int stopBits)
{
// Reset the serial terminal.
cfmakeraw(cfg);
// Set the serial baud rate.
switch (baudRate)
{
case 50:
{
cfsetispeed(cfg, B50);
cfsetospeed(cfg, B50);
break;
}
case 75:
{
cfsetispeed(cfg, B75);
cfsetospeed(cfg, B75);
break;
}
case 110:
{
cfsetispeed(cfg, B110);
cfsetospeed(cfg, B110);
break;
}
case 134:
{
cfsetispeed(cfg, B134);
cfsetospeed(cfg, B134);
break;
}
case 150:
{
cfsetispeed(cfg, B150);
cfsetospeed(cfg, B150);
break;
}
case 200:
{
cfsetispeed(cfg, B200);
cfsetospeed(cfg, B200);
break;
}
case 300:
{
cfsetispeed(cfg, B300);
cfsetospeed(cfg, B300);
break;
}
case 600:
{
cfsetispeed(cfg, B600);
cfsetospeed(cfg, B600);
break;
}
case 1200:
{
cfsetispeed(cfg, B1200);
cfsetospeed(cfg, B1200);
break;
}
case 1800:
{
cfsetispeed(cfg, B1800);
cfsetospeed(cfg, B1800);
break;
}
case 2400:
{
cfsetispeed(cfg, B2400);
cfsetospeed(cfg, B2400);
break;
}
case 4800:
{
cfsetispeed(cfg, B4800);
cfsetospeed(cfg, B4800);
break;
}
case 9600:
{
cfsetispeed(cfg, B9600);
cfsetospeed(cfg, B9600);
break;
}
case 19200:
{
cfsetispeed(cfg, B19200);
cfsetospeed(cfg, B19200);
break;
}
case 38400:
{
cfsetispeed(cfg, B38400);
cfsetospeed(cfg, B38400);
break;
}
case 57600:
{
cfsetispeed(cfg, B57600);
cfsetospeed(cfg, B57600);
break;
}
case 115200:
{
cfsetispeed(cfg, B115200);
cfsetospeed(cfg, B115200);
break;
}
case 230400:
{
cfsetispeed(cfg, B230400);
cfsetospeed(cfg, B230400);
break;
}
}
// Set the parity type.
switch (parityType | 32)
{
case 'n':
{
cfg->c_cflag &= ~PARENB;
break;
}
case 'e':
{
cfg->c_cflag |= PARENB;
cfg->c_cflag &= ~PARODD;
break;
}
case 'o':
{
cfg->c_cflag |= PARENB;
cfg->c_cflag |= PARODD;
break;
}
}
cfg->c_cflag &= ~CSIZE;
// Set the data bits.
switch (dataBits)
{
case 5:
{
cfg->c_cflag |= CS5;
break;
}
case 6:
{
cfg->c_cflag |= CS6;
break;
}
case 7:
{
cfg->c_cflag |= CS7;
break;
}
case 8:
{
cfg->c_cflag |= CS8;
break;
}
}
// Set the stop bits.
if (stopBits == 1)
cfg->c_cflag &= ~CSTOPB;
else
cfg->c_cflag |= CSTOPB;
// Set the serial terminal and return.
return tcsetattr(source, TCSANOW, cfg);
}
// Close serial terminal then exit the program.
void ExitProgram(int x)
{
if (sourceType[0] & 2)
{
tcflush(source[0], TCIOFLUSH);
close(source[0]);
}
if (sourceType[1] & 2)
{
tcflush(source[1], TCIOFLUSH);
close(source[1]);
}
printf("%s exiting.\n", programName);
exit(1);
}
int main(int argc, char **argv)
{
int i, n, w, clen[2], nonblock[2], baudRate, dataBits, stopBits;
unsigned char c, buf[MAXMESG], *dataPointer, parityType;
struct termios cfg;
struct sockaddr_in addr[4][4];
struct sigaction newact, oldact;
programName = argv[0];
if (argc != 7)
{
PrintHelp();
return 1;
}
for (i = 0; i < 2; i++)
{
sourceType[i] = 0;
switch (argv[3 * i + 1][1])
{
case 's':
sourceType[i] = 1;
case 'c':
bzero((char *)&(addr[i][0]), sizeof(addr[i][0]));
addr[i][0].sin_family = AF_INET;
addr[i][0].sin_addr.s_addr = inet_addr(argv[3 * i + 2]);
addr[i][0].sin_port = htons(atoi(argv[3 * i + 3]));
bzero((char *)&(addr[i][1]), sizeof(addr[i][1]));
addr[i][1].sin_family = AF_INET;
addr[i][1].sin_addr.s_addr = 0;
addr[i][1].sin_port = htons(0);
if ((source[i] = socket(AF_INET, SOCK_DGRAM, 0)) < 0)
{
fprintf(stderr, "%s: can't open datagram socket", programName);
return 3;
}
if (bind(source[i], (struct sockaddr *)&addr[i][!sourceType[i]], sizeof(addr[i][!sourceType[i]])) < 0)
{
fprintf(stderr, "%s: can't bind local address", programName);
return 4;
}
break;
case 'd':
sourceType[i] = 2;
if ((source[i] = open(argv[3 * i + 2], O_RDWR | O_NDELAY)) < 0)
{
fprintf(stderr, "%s: could not open device %s\n",
programName, argv[3 * i + 2]);
return -1;
}
n = sscanf(argv[3 * i + 3], "%d-%d%c%d", &baudRate, &dataBits, &parityType, &stopBits);
if (n < 4)
{
fprintf(stderr, "%s: invalid argument %1d from %s\n",
programName, read + 1, argv[3 * i + 3]);
return 3;
}
if (SetSerial(source[i], &cfg, baudRate, dataBits, parityType, stopBits) < 0)
{
fprintf(stderr, "%s: could not initialize device %s\n",
programName, argv[3 * i + 2]);
return 7;
}
break;
default:
PrintHelp();
return 2;
}
clen[i] = sizeof(addr[i][1]);
nonblock[i] = !(sourceType[i] & 1);
}
// Let ExitProgram function handle the SIGINT message(Generated by Ctrl+C).
signal(SIGINT, ExitProgram);
i = 0;
// Keep data forwarding until SIGINT message occurred.
while (1)
{
if (sourceType[i] & 2)
n = read(source[i], buf, MAXMESG);
else
{
n = recvfrom(source[i], buf, MAXMESG, nonblock[i] * MSG_DONTWAIT,
(struct sockaddr *)&addr[i][sourceType[i]], &clen[i]);
nonblock[i] = 1;
}
dataPointer = buf;
while (n > 0)
{
if (sourceType[!i] & 2)
w = write(source[!i], dataPointer, n);
else
w = sendto(source[!i], dataPointer, n, 0,
(struct sockaddr *)&addr[!i][sourceType[!i]], clen[!i]);
if (w > 0)
{
n -= w;
dataPointer += w;
}
else
{
fprintf(stderr, "%s: write error\n", programName);
break;
}
}
i = !i;
}
return 0;
}