如何在 C 中通过串行端口发送0xff字节?

Question

所以我想通过串行电缆发送一个0xff字节，该串行电缆触发计算机通过以太网电缆发回数据。代码如下

#include <stdio.h>
#include <stdlib.h>
#include<windows.h>
#include<winsock2.h>
#include <string.h>
#include <time.h>
#pragma comment(lib,"ws2_32.lib") //Winsock Library
#define BUFLEN 4097 //Max length of buffer
#define PORT 9090 //The port on which to listen for incoming data
int main()
{
BOOL Status;
HANDLE ComPort;
char str[20] = "\\.\COM";
char input[4] = "";
printf("Enter COM port: ");
fgets(input,4,stdin);
input[strcspn(input, "n")] = 0;
strncat(str,input, 5);
ComPort = CreateFile((const char*)str,                //port name
GENERIC_READ | GENERIC_WRITE, //Read/Write
0,                            // No Sharing
NULL,                         // No Security
OPEN_EXISTING,// Open existing port only
0,            // Non Overlapped I/O
NULL);        // Null for Comm Devices
if (ComPort == INVALID_HANDLE_VALUE){
printf("nError in opening serial port");
exit(EXIT_FAILURE);}
else{
printf("opening serial port successful");
}
DCB dcbSerialParams = { 0 }; // Initializing DCB structure
dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
Status = GetCommState(ComPort, &dcbSerialParams);
dcbSerialParams.BaudRate = CBR_115200;  // Setting BaudRate = 115200
dcbSerialParams.ByteSize = 8;         // Setting ByteSize = 8
dcbSerialParams.StopBits = ONESTOPBIT;// Setting StopBits = 1
dcbSerialParams.Parity   = NOPARITY;  // Setting Parity = None
SetCommState(ComPort, &dcbSerialParams);
COMMTIMEOUTS timeouts = { 0 };
timeouts.ReadIntervalTimeout         = MAXWORD; // in milliseconds
timeouts.ReadTotalTimeoutConstant    = 10000; // in milliseconds
timeouts.ReadTotalTimeoutMultiplier  = MAXWORD; // in milliseconds
timeouts.WriteTotalTimeoutConstant   = 0; // in milliseconds
timeouts.WriteTotalTimeoutMultiplier = 0; // in milliseconds
char lpBuffer[] = {255};
DWORD dNoOFBytestoWrite;         // No of bytes to write into the port
DWORD dNoOfBytesWritten;     // No of bytes written to the port
dNoOFBytestoWrite = sizeof(lpBuffer);
SOCKET s;
struct sockaddr_in server, si_other;
int slen , recv_len;
char buf[BUFLEN];
WSADATA wsa;
slen = sizeof(si_other) ;
//Initialise winsock
if (WSAStartup(MAKEWORD(2,2),&wsa) != 0)
{
printf("Failed. Error Code : %d",WSAGetLastError());
exit(EXIT_FAILURE);
}
//Create a socket
if((s = socket(AF_INET , SOCK_DGRAM , 0 )) == INVALID_SOCKET)
{
printf("nCould not create socket : %d" , WSAGetLastError());
exit(EXIT_FAILURE);
}
//Prepare the sockaddr_in structure
server.sin_family = AF_INET;
server.sin_addr.s_addr = INADDR_ANY;
server.sin_port = htons( PORT );
//Bind
if( bind(s ,(struct sockaddr *)&server , sizeof(server)) == SOCKET_ERROR)
{
printf("nBind failed with error code : %d" , WSAGetLastError());
exit(EXIT_FAILURE);
}
printf("nBinding successful");
DWORD timeout = 0.2 * 1000;//0.2 second ethernet timeout
setsockopt(s, SOL_SOCKET, SO_RCVTIMEO, (const char*)&timeout, sizeof timeout);
FILE * fPtr;
char filename[50] = "fpgadat.bin";
fPtr = fopen((const char*) filename, "wb");//Open file in wb (write) mode.
// fopen() return NULL if last operation was unsuccessful
if(fPtr == NULL)
{
// File not created hence exit
printf("Unable to create file.n");
exit(EXIT_FAILURE);
}
while(1)
{
time_t start = time(NULL);
Status = WriteFile(ComPort,        // Handle to the Serial port
lpBuffer,     // Data to be written to the port
dNoOFBytestoWrite,  //No of bytes to write
&dNoOfBytesWritten, //Bytes written
NULL);
if(Status == 0){
printf("nFailed to write to serial port");
return 0;
}else{
printf("nData successfully written to serial port");
}
printf("nWaiting for data from fpga...");
fflush(stdout);
memset(buf,'', BUFLEN);//clear the buffer by filling null, it might have previously received data
//try to receive some data, this is a blocking call
if ((recv_len = recvfrom(s, buf, BUFLEN, 0, (struct sockaddr *) &si_other, &slen)) == SOCKET_ERROR)
{
printf("nEthernet connection time-out");
break;
}
fwrite(buf , 1 , sizeof(buf) , fPtr );
printf("%.2fn", (double)(time(NULL) - start));
}
//close file descriptors
fclose(fPtr);
CloseHandle(ComPort);
closesocket(s);
WSACleanup();
}

我似乎总是在以太网上收到超时错误。我认为这是因为我没有发送必要的0xff字节来触发第二台计算机通过以太网发回数据。问题可能是什么？

Answer 1

在使用此代码之前，我不确定您在做什么，但我建议使用 Com0com、PortMon 或 Wire Shark 来监控您的 Com 端口和以太网。它会让你的生活更轻松。

同样在您的问题中，您应该告诉我们您的代码的结果是什么，以便我们可以更好地了解正在发生的事情。

链接 https://www.xanthium.in/Serial-Port-Programming-using-Win32-API 与您尝试执行的操作相同。

您确定选择了正确的 com 端口吗？

您的代码显示您正在尝试写入连接到另一台正在侦听串行端口的 PC 的串行端口。您是否确定另一台 PC 正在使用相同的波特和控制线进行侦听。(它可能设置为某些默认值。您应该首先尝试在两台PC上使用终端.exe或类似的东西，以查看您的串行通信是否在两台PC之间工作。接下来，您应该创建一个仅发送到com端口的应用程序，并使用终端仿真器在另一台PC上侦听它是否到达。