Windows WriteFile and ReadFile interferes with each other - windows

Question

I have two threads, one calls WriteFile, the other calls ReadFile, both uses the same serial port at 115200. What I have found repeatedly is that when I add more sequential WriteFile calls in the writing thread, is that I have an increased number of check-sum failures i.e. corrupt data. If I add delays between the WriteFile calls in the writing thread (using CBaseDLIMessage::CrossSleep(20) ), the check-sum errors reduce or even completely go away (depending on the sleep time), however the problem comes back when adding additional WriteFile methods.
Is it possible that the WriteFile method can somehow write data into a shared buffer, which is also used for reading (at driver level), which subsequently corrupts my read data?
My serial setup code looks like this:
CommHandle OpenSerialPort(int nId, long baud)
{
#if defined(USE_WINDOWS_SERIAL_PORT_LIB)
char szCOM[16];
/* COM waiting */
COMMTIMEOUTS g_cto =
{
MAXDWORD, /* ReadIntervalTimeOut */
0, /* ReadTotalTimeOutMultiplier */
0, /* ReadTotalTimeOutConstant */
0, /* WriteTotalTimeOutMultiplier */
0 /* WriteTotalTimeOutConstant */
};
/* COM configuration */
DCB g_dcb =
{
sizeof(DCB), /* DCBlength */
baud, /* BaudRate */
TRUE, /* fBinary */
FALSE, /* fParity */
FALSE, /* fOutxCtsFlow */
FALSE, /* fOutxDsrFlow */
DTR_CONTROL_DISABLE, /* fDtrControl */
FALSE, /* fDsrSensitivity */
FALSE, /* fTXContinueOnXoff */
FALSE, /* fOutX */
FALSE, /* fInX */
FALSE, /* fErrorChar */
FALSE, /* fNull */
RTS_CONTROL_DISABLE, /* fRtsControl */
FALSE, /* fAbortOnError */
0, /* fDummy2 */
0, /* wReserved */
0x100, /* XonLim */
0x100, /* XoffLim */
8, /* ByteSize */
NOPARITY, /* Parity */
ONESTOPBIT, /* StopBits */
0x11, /* XonChar */
0x13, /* XoffChar */
'?', /* ErrorChar */
0x1A, /* EofChar */
0x10 /* EvtChar */
};
//cout << "COM:::" << nId;
sprintf(szCOM, "\\\\.\\COM%d", nId);
HANDLE hCOM = CreateFile(szCOM, /* lpFileName */
GENERIC_READ|GENERIC_WRITE, /* dwDesiredAccess */
0, /* dwShareMode */
NULL, /* lpSecurityAttributes */
OPEN_EXISTING, /* dwCreationDisposition */
FILE_ATTRIBUTE_SYSTEM, /* dwFlagsAndAttributes */
NULL); /* hTemplateFile */
//std::cout << "COM: " << (int)nId << "\n";
if(hCOM == INVALID_HANDLE_VALUE)
{
//std::cout << "INVALID_HANDLE_VALUE \n" ;
DWORD err = GetLastError();
if (err == ERROR_FILE_NOT_FOUND)
{
std::cout << "Error: Failed to open COM[" << nId << "]\n";
}
else if(err == ERROR_INVALID_NAME)
{
std::cout << "\nError: \n%s 'filename, directory name, or volume label syntax is incorrect'\n"; //error code 0x7B
}
else
{
//cout << "\nHandle creation error code: %x\n" << err;
}
return 0;
}
else
{
std::cout << "COM[" << nId << "] OPEN. Baud: " << baud <<"\n";
}
// COM buffer size
SetupComm(hCOM, RX_SIZE, TX_SIZE);
// COM config
if(!SetCommTimeouts(hCOM, &g_cto) || !SetCommState(hCOM, &g_dcb))
{
CloseHandle(hCOM);
return 0;
}
// COM buffer purge
PurgeComm(hCOM, PURGE_TXCLEAR|PURGE_RXCLEAR|PURGE_TXABORT|PURGE_RXABORT);
EscapeCommFunction(hCOM, SETDTR);
return hCOM;
#else
wxSerialPort *pwxSerialPort = new wxSerialPort();
char szPort[32];
sprintf(szPort,"com%d", nId);
if(pwxSerialPort->Open(szPort) < 0) {
return 0;
}
// set the baudrate
pwxSerialPort->SetBaudRate((wxBaud)baud);
return pwxSerialPort;
#endif
}
int CloseSerialPort(CommHandle hSerialPort)
{
#if defined(USE_WINDOWS_SERIAL_PORT_LIB)
CloseHandle(hSerialPort);
return 1;
#else
hSerialPort->Close();
delete hSerialPort;
return 1;
#endif
}
int WriteDataToSerialPort(CommHandle hSerialPort, void *pMsg, unsigned short messageLength, unsigned int *pBytesWritten)
{
*pBytesWritten = 0;
if(hSerialPort == 0)
{
//cout << "hSerialPort ====== 0";
return -1;
}
#if defined(USE_WINDOWS_SERIAL_PORT_LIB)
return WriteFile(hSerialPort, (char*)pMsg, messageLength, (DWORD*)pBytesWritten, NULL);
#else
*pBytesWritten = hSerialPort->Write((char*)pMsg, messageLength);
return 1;
#endif
}
int ReadDataFromSerialPort(CommHandle hSerialPort, void *pMsg, unsigned short messageLength, unsigned int *pBytesRead)
{
unsigned short i;
*pBytesRead = 0;
i = 0;
if(hSerialPort == 0)
{
return -1;
}
#if defined(USE_WINDOWS_SERIAL_PORT_LIB)
return ReadFile(hSerialPort, (char*)pMsg, messageLength, (DWORD*)pBytesRead, NULL);
#else
*pBytesRead = hSerialPort->Read((char*)pMsg, messageLength);
return 1;
#endif
}

Answer 1

Communication through serial port is slow.
You should use WriteFileEx instead of WriteFile.
You can specify a routine which may execute when the writting(transmitting) is completed or failed.
If you write next data after that routine has been executed, overflow of data may not be occured.