我们正在尝试在 Javascript 上编写 GPS 设备侦听器代码。
在此过程中,我们无法开发正确的 CRC-ITU 错误检查脚本。协议文档生成crc码的解释如下
终端或服务器可以使用校验码来区分
接收到的信息是否有误。为了防止错误
数据传输过程中发生的情况,对数据添加错误检查
误操作,从而提高安全性和效率
系统。校验码由CRC-ITU校验方法生成。
协议结构中数据的校验码,来自
数据包长度到信息序列号(包括“数据包
长度”和“信息序列号”),是CRC-ITU的值。 CRC
计算接收到的信息时发生错误,接收方
将忽略并丢弃该数据包。
我们参考了协议文档中给出的C代码示例 -
// calculate the 16-bit CRC of data with predetermined length.
U16 GetCrc16(const U8* pData, int nLength)
{
U16 fcs = 0xffff; // initialization
while(nLength>0)
{
fcs = (fcs >> 8) ^ crctab16[(fcs ^ *pData) & 0xff];
nLength--;
pData++;
}
return ~fcs; // negated
}
数组 crctab16 与我们的代码示例中提到的数组相同
Incoming data string comes in following format
Example of data packet sent by the terminal 78 78 0D 01 01 23 45 67 89 01 23 45 00 01 8C DD 0D 0A
Explanation
Start Bit - 0x78 0x78
Length - 0x0D
Protocol - 0x01
Terminal ID - 0x01 0x23 0x45 0x67 0x89 0x01 0x23 0x45
Serial No - 0x00 0x01
Error - 0x8C 0xDD
Stop Bit - 0x0D 0x0A
我们的 JavaScript 代码如下
var net = require('net');
net.createServer(function(socket)
{
socket.setEncoding('hex');
// New client connection event
socket.on('connect', function(data)
// Incoming data event
socket.on('data', function(data)
{
console.log("Client said: " + data); // server log
data_p = data.substring(4,28);
err_code = crc16(data_p);
console.log("error: " + err_code);
});
// Disconnect event
socket.on('end', function()
{
//Log it to the server output
console.log("someone left us." + socket.remoteAddress);
});
}).listen(3006);
console.log("TCP ECHO SERVER STARTED ON 3006");
function crc16(buf)
{
var crcTable =
[
0X0000, 0X1189, 0X2312, 0X329B, 0X4624, 0X57AD, 0X6536, 0X74BF, 0X8C48, 0X9DC1, 0XAF5A,
0XBED3, 0XCA6C, 0XDBE5, 0XE97E, 0XF8F7, 0X1081, 0X0108, 0X3393, 0X221A, 0X56A5, 0X472C,
0X75B7, 0X643E, 0X9CC9, 0X8D40, 0XBFDB, 0XAE52, 0XDAED, 0XCB64, 0XF9FF, 0XE876, 0X2102,
0X308B, 0X0210, 0X1399, 0X6726, 0X76AF, 0X4434, 0X55BD, 0XAD4A, 0XBCC3, 0X8E58, 0X9FD1,
0XEB6E, 0XFAE7, 0XC87C, 0XD9F5, 0X3183, 0X200A, 0X1291, 0X0318, 0X77A7, 0X662E, 0X54B5,
0X453C, 0XBDCB, 0XAC42, 0X9ED9, 0X8F50, 0XFBEF, 0XEA66, 0XD8FD, 0XC974, 0X4204, 0X538D,
0X6116, 0X709F, 0X0420, 0X15A9, 0X2732, 0X36BB, 0XCE4C, 0XDFC5, 0XED5E, 0XFCD7, 0X8868,
0X99E1, 0XAB7A, 0XBAF3, 0X5285, 0X430C, 0X7197, 0X601E, 0X14A1, 0X0528, 0X37B3, 0X263A,
0XDECD, 0XCF44, 0XFDDF, 0XEC56, 0X98E9, 0X8960, 0XBBFB, 0XAA72, 0X6306, 0X728F, 0X4014,
0X519D, 0X2522, 0X34AB, 0X0630, 0X17B9, 0XEF4E, 0XFEC7, 0XCC5C, 0XDDD5, 0XA96A, 0XB8E3,
0X8A78, 0X9BF1, 0X7387, 0X620E, 0X5095, 0X411C, 0X35A3, 0X242A, 0X16B1, 0X0738, 0XFFCF,
0XEE46, 0XDCDD, 0XCD54, 0XB9EB, 0XA862, 0X9AF9, 0X8B70, 0X8408, 0X9581, 0XA71A, 0XB693,
0XC22C, 0XD3A5, 0XE13E, 0XF0B7, 0X0840, 0X19C9, 0X2B52, 0X3ADB, 0X4E64, 0X5FED, 0X6D76,
0X7CFF, 0X9489, 0X8500, 0XB79B, 0XA612, 0XD2AD, 0XC324, 0XF1BF, 0XE036, 0X18C1, 0X0948,
0X3BD3, 0X2A5A, 0X5EE5, 0X4F6C, 0X7DF7, 0X6C7E, 0XA50A, 0XB483, 0X8618, 0X9791, 0XE32E,
0XF2A7, 0XC03C, 0XD1B5, 0X2942, 0X38CB, 0X0A50, 0X1BD9, 0X6F66, 0X7EEF, 0X4C74, 0X5DFD,
0XB58B, 0XA402, 0X9699, 0X8710, 0XF3AF, 0XE226, 0XD0BD, 0XC134, 0X39C3, 0X284A, 0X1AD1,
0X0B58, 0X7FE7, 0X6E6E, 0X5CF5, 0X4D7C, 0XC60C, 0XD785, 0XE51E, 0XF497, 0X8028, 0X91A1,
0XA33A, 0XB2B3, 0X4A44, 0X5BCD, 0X6956, 0X78DF, 0X0C60, 0X1DE9, 0X2F72, 0X3EFB, 0XD68D,
0XC704, 0XF59F, 0XE416, 0X90A9, 0X8120, 0XB3BB, 0XA232, 0X5AC5, 0X4B4C, 0X79D7, 0X685E,
0X1CE1, 0X0D68, 0X3FF3, 0X2E7A, 0XE70E, 0XF687, 0XC41C, 0XD595, 0XA12A, 0XB0A3, 0X8238,
0X93B1, 0X6B46, 0X7ACF, 0X4854, 0X59DD, 0X2D62, 0X3CEB, 0X0E70, 0X1FF9, 0XF78F, 0XE606,
0XD49D, 0XC514, 0XB1AB, 0XA022, 0X92B9, 0X8330, 0X7BC7, 0X6A4E, 0X58D5, 0X495C, 0X3DE3,
0X2C6A, 0X1EF1, 0X0F78
];
crcX = parseInt("FFFF",16);
cr1 = parseInt("FF",16);
cr2 = parseInt("FFFF",16);
i = 0;
while(i < buf.length)
{
str = buf.substring(i,i+4);
console.log("str "+str);
str_hex = parseInt(str,16);
j = (crcX ^ str_hex) & cr1;
crcX = (crcX >> 8) ^ crcTable[j] ;
i = i + 4;
}
crcX = ~crcX;
console.log("crcX - " + crcX.toString(16));
return crcX;
}
请找到下面的输入字符串对以及函数 crc16 生成的相应代码
78780d01035889905017664600267bf90d0a - 7bf9
78780d010358899050176646002ab1950d0a - b195
78780d010358899050176646002ba01c0d0a - a01c
请帮助我们找出代码中的错误。
非常感谢。