無法接收串行數據

Question

我修改了Windows平臺下C（codeblocks/mingw）中其他人編寫的串行通信環回代碼。我能夠正確發送數據。我通過打開終端軟件來驗證這一點。但我無法收到數據。在下面的代碼中，我從ReadFile（）的輸入緩衝區998中讀取錯誤消息錯誤。不知道錯誤是什麼。 我正在使用兩個CP210x USB串行模塊並將TxD連接到另一個的RxD。

#include <windows.h> 
#include <stdlib.h> 
#include <stdio.h> 
#include <string.h> 
#include <commdlg.h> 
//#include <windef.h> 
#include <time.h> 

int nread,nwrite; 

void myDelay(unsigned int mseconds) 
{ 
    clock_t goal = mseconds + clock(); 
    while (goal > clock()); 
} 

int main(int argc, char* argv[]) 
{ 
    HANDLE hSerial; 
    COMMTIMEOUTS timeouts; 
    COMMCONFIG dcbSerialParams; 
    char *words, *buffRead, *buffWrite; 
    DWORD dwBytesWritten, dwBytesRead; 

    if(argc<3) 
    { 
     printf("Enter the com port as command line parameter and t for transmitter and r for receiver\n"); 
     printf("Example: Serial.exe com4 t\n"); 
     return(1); 
    } 
    hSerial = CreateFile(argv[1],GENERIC_READ | GENERIC_WRITE,0,NULL,OPEN_EXISTING,FILE_ATTRIBUTE_NORMAL,NULL); 

    if (hSerial == INVALID_HANDLE_VALUE) 
    { 
     if (GetLastError() == ERROR_FILE_NOT_FOUND) 
     { 
      printf(" serial port does not exist \n"); 
     } 
     else 
     { 
      printf(" some other error occured\n"); 
     } 

     return(1); 
    } 


    if (!GetCommState(hSerial, &dcbSerialParams.dcb)) 
    { 
     printf("error getting state \n"); 
     return(1); 
    } 

    dcbSerialParams.dcb.DCBlength = sizeof(dcbSerialParams.dcb); 

    // Set various serial port parameters. 

    dcbSerialParams.dcb.BaudRate = CBR_9600; 
    dcbSerialParams.dcb.ByteSize = 8; 
    dcbSerialParams.dcb.StopBits = ONESTOPBIT; 
    dcbSerialParams.dcb.Parity = NOPARITY; 

    dcbSerialParams.dcb.fBinary = TRUE; 
    dcbSerialParams.dcb.fDtrControl = DTR_CONTROL_DISABLE; 
    dcbSerialParams.dcb.fRtsControl = RTS_CONTROL_DISABLE; 
    dcbSerialParams.dcb.fOutxCtsFlow = FALSE; 
    dcbSerialParams.dcb.fOutxDsrFlow = FALSE; 
    dcbSerialParams.dcb.fDsrSensitivity= FALSE; 
    dcbSerialParams.dcb.fAbortOnError = TRUE; 

    if (!SetCommState(hSerial, &dcbSerialParams.dcb)) 
    { 
     printf(" error setting serial port state \n"); 
     return(1); 
    } 


    GetCommTimeouts(hSerial,&timeouts); 
    timeouts.ReadIntervalTimeout = 50; 
    timeouts.ReadTotalTimeoutConstant = 50; 
    timeouts.ReadTotalTimeoutMultiplier = 10; 
    timeouts.WriteTotalTimeoutConstant = 50; 
    timeouts.WriteTotalTimeoutMultiplier= 10; 

    if(!SetCommTimeouts(hSerial, &timeouts)) 
    { 
     printf("error setting port state \n"); 
     return(1); 
    } 

    while(1) 
    { 
     // Use a delay of 500 msec 
     myDelay(500); 
     if(!strcmp(argv[2],"t")) 
     { 

      printf("Write Mode\n"); 
      //****************Write Operation*********************// 
      words = "This is a string to be written to serial port COM1"; 
      nwrite = strlen(words); 

      buffWrite = words; 
      dwBytesWritten = 0; 

      if (!WriteFile(hSerial, buffWrite, nwrite, &dwBytesWritten, NULL)) 
      { 
       printf("error writing to output buffer \n"); 
       return(1); 
      } 

     } 


//***************Read Operation******************// 

     else 
     { 
      dwBytesRead = 0; 
      nread = strlen(words); 

      if (!ReadFile(hSerial, buffRead, nread, &dwBytesRead, NULL)) 
      { 
       printf("error reading from input buffer %d\n", GetLastError()); 
       continue; 
      } 
      printf("Data read from read buffer is \n %s \n",buffRead); 

     } 
    } 
    CloseHandle(hSerial); 
    return(0); 

} 

Answer 1

讀取和寫入COM端口會互相阻塞，使得您的讀取在FIFO耗盡時幾乎總是超時。也可能有一些數據在FIFO中已經如此...如果您發送和接收的數據量過大，數據丟失更有可能以這種方式進行。非螺紋COM端口訪問

這裏小古例如

//--------------------------------------------------------------------------- 
//--- port class ver: 1.0 ------------------------------------------------ 
//--------------------------------------------------------------------------- 
#ifndef _port_h 
#define _port_h 
//--------------------------------------------------------------------------- 
class port 
     { 
public: HANDLE  hnd; 
     AnsiString error; 
     DWORD  rlen,wlen,err; 
     DCB   rs232_state; 
     COMMPROP  properties; 
     COMMTIMEOUTS timeouts; 
     COMSTAT  stat; 
     port(); 
     ~port(); 
     int open(AnsiString name); 
     void close(); 
     int get_stat();  // err,stat 
     int get_timeouts(); // timeouts 
     int set_timeouts(); 
     int get_properties(); // properties 
     int get_rs232_state(); // rs232_state 
     int set_rs232_state(); 
     void rst_rs232_state(); 
     void out(BYTE data) { WriteFile(hnd,&data,1,&wlen,NULL); } 
     void in (BYTE *data) { ReadFile (hnd, data,1,&rlen,NULL); } 
     void in (char *data) { ReadFile (hnd, data,1,&rlen,NULL); } 
     void out(BYTE *data,DWORD len) { WriteFile(hnd,data,len,&wlen,NULL); } 
     void in (BYTE *data,DWORD len) { ReadFile (hnd,data,len,&rlen,NULL); } 
     }; 
//--------------------------------------------------------------------------- 
port::port() 
     { 
     rlen=0; 
     wlen=0; 
     err =0; 
     error=""; 
     hnd=NULL; 
     rst_rs232_state(); 
     } 
//--------------------------------------------------------------------------- 
port::~port() 
     { 
     close(); 
     } 
//--------------------------------------------------------------------------- 
int port::open(AnsiString name) 
     { 
     close(); 
     rlen=0; 
     wlen=0; 
     hnd=CreateFile(name.c_str(),GENERIC_READ | GENERIC_WRITE,0,NULL,OPEN_ALWAYS,0,NULL); 
     if (hnd==NULL) return 0; 
     get_timeouts(); 
     get_properties(); 
     get_rs232_state(); 

     timeouts.ReadIntervalTimeout; 
     timeouts.ReadTotalTimeoutMultiplier; 
     timeouts.ReadTotalTimeoutConstant; 
     timeouts.WriteTotalTimeoutMultiplier; 
     timeouts.WriteTotalTimeoutConstant; 

     properties.wPacketLength; 
     properties.wPacketVersion; 
     properties.dwServiceMask; 
     properties.dwReserved1; 
     properties.dwMaxTxQueue; 
     properties.dwMaxRxQueue; 
     properties.dwMaxBaud; 
     properties.dwProvSubType; 
     properties.dwProvCapabilities; 
     properties.dwSettableParams; 
     properties.dwSettableBaud; 
     properties.wSettableData; 
     properties.wSettableStopParity; 
     properties.dwCurrentTxQueue; 
     properties.dwCurrentRxQueue; 
     properties.dwProvSpec1; 
     properties.dwProvSpec2; 
     properties.wcProvChar[1]; 

     return 1; 
     } 
//--------------------------------------------------------------------------- 
void port::close() 
     { 
     if (hnd==NULL) return; 
     CloseHandle(hnd); 
     hnd=NULL; 
     } 
//--------------------------------------------------------------------------- 
int port::get_stat() 
     { 
     if (ClearCommError(hnd,&err,&stat)) return 1; 
     error=GetLastError(); 
     return 0; 
     } 
//--------------------------------------------------------------------------- 
int port::get_timeouts() 
     { 
     if (GetCommTimeouts(hnd,&timeouts)) return 1; 
     error=GetLastError(); 
     get_stat(); 
     return 0; 
     } 
//--------------------------------------------------------------------------- 
int port::set_timeouts() 
     { 
     if (SetCommTimeouts(hnd,&timeouts)) return 1; 
     error=GetLastError(); 
     get_stat(); 
     return 0; 
     } 
//--------------------------------------------------------------------------- 
int port::get_properties() 
     { 
     if (GetCommProperties(hnd,&properties)) return 1; 
     error=GetLastError(); 
     get_stat(); 
     return 0; 
     } 
//--------------------------------------------------------------------------- 
int port::get_rs232_state() 
     { 
     if (GetCommState(hnd,&rs232_state)) return 1; 
     error=GetLastError(); 
     get_stat(); 
     return 0; 
     } 
//--------------------------------------------------------------------------- 
int port::set_rs232_state() 
     { 
     if (SetCommState(hnd,&rs232_state)) return 1; 
     error=GetLastError(); 
     get_stat(); 
     return 0; 
     } 
//--------------------------------------------------------------------------- 
void port::rst_rs232_state() 
     { 
     rs232_state.BaudRate = CBR_9600; 
     rs232_state.ByteSize = 8; 
     rs232_state.Parity  = NOPARITY; 
     rs232_state.StopBits = ONESTOPBIT; 
     rs232_state.fOutxCtsFlow= FALSE; 
     rs232_state.fOutxDsrFlow= FALSE; 
     rs232_state.fOutX  = FALSE; 
     rs232_state.fInX  = FALSE; 
     rs232_state.fBinary  = FALSE; 
     rs232_state.fRtsControl = RTS_CONTROL_DISABLE; 
     } 
//---------------------------------------------------------------------------//--------------------------------------------------------------------------- 
//---------------------------------------------------------------------------//--------------------------------------------------------------------------- 
//--------------------------------------------------------------------------- 
#endif 
//--------------------------------------------------------------------------- 

正是在C++/VCL所以才改寫AnsiString到char*或你有，改變它的文件程序到你的任何字符串類型。如果您無法訪問課程，請重寫爲C。用法很簡單：

// globals and init 
port com; 
com.open("COM2"); 
com.timeouts.ReadIntervalTimeout  =10; 
com.timeouts.ReadTotalTimeoutMultiplier =10; 
com.timeouts.ReadTotalTimeoutConstant =10; 
com.timeouts.WriteTotalTimeoutMultiplier=10; 
com.timeouts.WriteTotalTimeoutConstant =10; 
com.set_timeouts(); 

// send/recv 
char q; 
com.out(`x`); // send x 
com.in (&q); // recv ... 

您應該使用線程來解決這個問題，因爲沒有線程阻塞通信。反正不爲環回你應該線程：

1. 組中的兩個COM端口相同的協議
2. 總是先發送，然後接收
3. 設置足夠小超時（不阻塞太長）
4. 出現數據丟失和超時（和處理這樣...不阻斷其發送）
5. 僅發送BYTES不是所有的COM端口有沿途大的FIFO ...

更安全做閱讀內螺紋......像：

volatile bool _stop=false; // set this to true when you want to exit 
unsigned long __stdcall thread_com(LPVOID p) 
     { 
     char q; 
     for (;!_stop;) 
     { 
     com.in (&q); // recv ... 
     if (q<32) q=`.`; // data loss due to timeout if not sending `0..31` of coarse 
     Sleep(1); // just not to burn CPU ... 
     } 
     } 

HANDLE thread_com_hnd=CreateThread(0,0,thread_com,NULL,0,0); // do this only after COM port is initialized