值 事件描述EV_BREAKA break was detected on input.EV_CTS The CTS (clear-to-send) signal changed state.EV_DSRThe DSR(data-set-ready) signal changed state.EV_ERRA line-status error occurred. Line-status errors are CE_FRAME, CE_OVERRUN, and CE_RXPARITY.EV_RING A ring indicator was detected.EV_RLSD The RLSD (receive-line-signal-detect) signal changed state.EV_RXCHARA character was received and placed in the input buffer.EV_RXFLAG The event character was received and placed in the input buffer. The event character is specified in the device's DCB structure, which is applied to a serial port by using the SetCommState function.EV_TXEMPTYThe last character in the output buffer was sent. 在设置好事件掩模后，我们就可以利用WaitCommEvent()函数来等待串口上发生事件，其函数原型为：
CMultiThreadComDlg dlg; m_pMainWnd = &dlg; int nResponse = dlg.DoModal(); if (nResponse == IDOK) { // TODO: Place code here to handle when the dialog is // dismissed with OK } else if (nResponse == IDCANCEL) { // TODO: Place code here to handle when the dialog is // dismissed with Cancel } return FALSE; } 此后我们在对话框CMultiThreadComDlg的初始化函数OnInitDialog中启动两个分别处理COM1和COM2的线程：
BOOL CMultiThreadComDlg::OnInitDialog() { CDialog::OnInitDialog(); // Add "About..." menu item to system menu.
// IDM_ABOUTBOX must be in the system command range. ASSERT((IDM_ABOUTBOX & 0xFFF0) == IDM_ABOUTBOX); ASSERT(IDM_ABOUTBOX < 0xF000);
// Set the icon for this dialog. The framework does this automatically // when the application's main window is not a dialog SetIcon(m_hIcon, TRUE); // Set big icon SetIcon(m_hIcon, FALSE); // Set small icon
#define WM_COMM_BREAK_DETECTED WM_USER+1 // A break was detected on input. #define WM_COMM_CTS_DETECTED WM_USER+2 // The CTS (clear-to-send) signal changed state. #define WM_COMM_DSR_DETECTED WM_USER+3 // The DSR (data-set-ready) signal changed state. #define WM_COMM_ERR_DETECTED WM_USER+4 // A line-status error occurred. Line-status errors are CE_FRAME, CE_OVERRUN, and CE_RXPARITY. #define WM_COMM_RING_DETECTED WM_USER+5 // A ring indicator was detected. #define WM_COMM_RLSD_DETECTED WM_USER+6 // The RLSD (receive-line-signal-detect) signal changed state. #define WM_COMM_RXCHAR WM_USER+7 // A character was received and placed in the input buffer. #define WM_COMM_RXFLAG_DETECTED WM_USER+8 // The event character was received and placed in the input buffer. #define WM_COMM_TXEMPTY_DETECTED WM_USER+9 // The last character in the output buffer was sent.
class CSerialPort { public: // contruction and destruction CSerialPort(); virtual ~CSerialPort();
// Event array. // One element is used for each event. There are two event handles for each port. // A Write event and a receive character event which is located in the overlapped structure (m_ov.hEvent). // There is a general shutdown when the port is closed. HANDLE m_hEventArray[3];
// get a handle to the port m_hComm = CreateFile(szPort, // communication port string (COMX) GENERIC_READ GENERIC_WRITE, // read/write types 0, // comm devices must be opened with exclusive access NULL, // no security attributes OPEN_EXISTING, // comm devices must use OPEN_EXISTING FILE_FLAG_OVERLAPPED, // Async I/O 0); // template must be 0 for comm devices
if (m_hComm == INVALID_HANDLE_VALUE) { // port not found delete []szPort; delete []szBaud; return FALSE; }
// set the timeout values m_CommTimeouts.ReadIntervalTimeout = 1000; m_CommTimeouts.ReadTotalTimeoutMultiplier = 1000; m_CommTimeouts.ReadTotalTimeoutConstant = 1000; m_CommTimeouts.WriteTotalTimeoutMultiplier = 1000; m_CommTimeouts.WriteTotalTimeoutConstant = 1000;
// configure if (SetCommTimeouts(m_hComm, &m_CommTimeouts)) { if (SetCommMask(m_hComm, dwCommEvents)) { if (GetCommState(m_hComm, &m_dcb)) { m_dcb.fRtsControl = RTS_CONTROL_ENABLE; // set RTS bit high! if (BuildCommDCB(szBaud, &m_dcb)) { if (SetCommState(m_hComm, &m_dcb)) ; // normal Operation... continue else ProcessErrorMessage("SetCommState()"); } else ProcessErrorMessage("BuildCommDCB()"); } else ProcessErrorMessage("GetCommState()"); } else ProcessErrorMessage("SetCommMask()"); } else ProcessErrorMessage("SetCommTimeouts()");
delete []szPort; delete []szBaud;
// flush the port PurgeComm(m_hComm, PURGE_RXCLEAR PURGE_TXCLEAR PURGE_RXABORT PURGE_TXABORT);
UINT CSerialPort::CommThread(LPVOID pParam) { // Cast the void pointer passed to the thread back to // a pointer of CSerialPort class CSerialPort *port = (CSerialPort*)pParam;
// Set the status variable in the dialog class to // TRUE to indicate the thread is running. port->m_bThreadAlive = TRUE;
// Clear comm buffers at startup if (port->m_hComm) // check if the port is opened PurgeComm(port->m_hComm, PURGE_RXCLEAR PURGE_TXCLEAR PURGE_RXABORT PURGE_TXABORT);
// begin forever loop. This loop will run as long as the thread is alive. for (;;) { // Make a call to WaitCommEvent(). This call will return immediatly // because our port was created as an async port (FILE_FLAG_OVERLAPPED // and an m_OverlappedStructerlapped structure specified). This call will cause the // m_OverlappedStructerlapped element m_OverlappedStruct.hEvent, which is part of the m_hEventArray to // be placed in a non-signeled state if there are no bytes available to be read, // or to a signeled state if there are bytes available. If this event handle // is set to the non-signeled state, it will be set to signeled when a // character arrives at the port.
if (!bResult) { // If WaitCommEvent() returns FALSE, process the last error to determin // the reason.. switch (dwError = GetLastError()) { case ERROR_IO_PENDING: { // This is a normal return value if there are no bytes // to read at the port. // Do nothing and continue break; } case 87: { // Under Windows NT, this value is returned for some reason. // I have not investigated why, but it is also a valid reply // Also do nothing and continue. break; } default: { // All other error codes indicate a serious error has // occured. Process this error. port->ProcessErrorMessage("WaitCommEvent()"); break; } } } else { // If WaitCommEvent() returns TRUE, check to be sure there are // actually bytes in the buffer to read. // // If you are reading more than one byte at a time from the buffer // (which this program does not do) you will have the situation occur // where the first byte to arrive will cause the WaitForMultipleObjects() // function to stop waiting. The WaitForMultipleObjects() function // resets the event handle in m_OverlappedStruct.hEvent to the non-signelead state // as it returns. // // If in the time between the reset of this event and the call to // ReadFile() more bytes arrive, the m_OverlappedStruct.hEvent handle will be set again // to the signeled state. When the call to ReadFile() occurs, it will // read all of the bytes from the buffer, and the program will // loop back around to WaitCommEvent(). // // At this point you will be in the situation where m_OverlappedStruct.hEvent is set, // but there are no bytes available to read. If you proceed and call // ReadFile(), it will return immediatly due to the async port setup, but // GetOverlappedResults() will not return until the next character arrives. // // It is not desirable for the GetOverlappedResults() function to be in // this state. The thread shutdown event (event 0) and the WriteFile() // event (Event2) will not work if the thread is blocked by GetOverlappedResults(). // // The solution to this is to check the buffer with a call to ClearCommError(). // This call will reset the event handle, and if there are no bytes to read // we can loop back through WaitCommEvent() again, then proceed. // If there are really bytes to read, do nothing and proceed.
if (comstat.cbInQue == 0) continue; } // end if bResult
// Main wait function. This function will normally block the thread // until one of nine events occur that require action. Event = WaitForMultipleObjects(3, port->m_hEventArray, FALSE, INFINITE);
switch (Event) { case 0: { // Shutdown event. This is event zero so it will be // the higest priority and be serviced first.
port->m_bThreadAlive = FALSE;
// Kill this thread. break is not needed, but makes me feel better. AfxEndThread(100); break; } case 1: // read event { GetCommMask(port->m_hComm, &CommEvent); if (CommEvent &EV_CTS) ::SendMessage(port->m_pOwner->m_hWnd, WM_COMM_CTS_DETECTED, (WPARAM)0, (LPARAM)port->m_nPortNr); if (CommEvent &EV_RXFLAG) ::SendMessage(port->m_pOwner->m_hWnd, WM_COMM_RXFLAG_DETECTED,(WPARAM)0, (LPARAM)port->m_nPortNr); if (CommEvent &EV_BREAK) ::SendMessage(port->m_pOwner->m_hWnd, WM_COMM_BREAK_DETECTED,(WPARAM)0, (LPARAM)port->m_nPortNr); if (CommEvent &EV_ERR) ::SendMessage(port->m_pOwner->m_hWnd, WM_COMM_ERR_DETECTED, (WPARAM)0, (LPARAM)port->m_nPortNr); if (CommEvent &EV_RING) ::SendMessage(port->m_pOwner->m_hWnd, WM_COMM_RING_DETECTED,(WPARAM)0, (LPARAM)port->m_nPortNr); if (CommEvent &EV_RXCHAR) // Receive character event from port. ReceiveChar(port, comstat); break; } case 2: // write event { // Write character event from port WriteChar(port); break; } } // end switch } // close forever loop return 0; } 下列三个函数用于对串口线程进行启动、挂起和恢复：
bResult = WriteFile(port->m_hComm, // Handle to COMM Port port->m_szWriteBuffer, // Pointer to message buffer in calling finction strlen((char*)port->m_szWriteBuffer), // Length of message to send &BytesSent, // Where to store the number of bytes sent &port->m_ov); // Overlapped structure
// deal with any error codes if (!bResult) { DWORD dwError = GetLastError(); switch (dwError) { case ERROR_IO_PENDING: { // continue to GetOverlappedResults() BytesSent = 0; bWrite = FALSE; break; } default: { // all other error codes port->ProcessErrorMessage("WriteFile()"); } } } else { LeaveCriticalSection(&port->m_csCommunicationSync); } } // end if(bWrite)
if (!bWrite) { bWrite = TRUE;
bResult = GetOverlappedResult(port->m_hComm, // Handle to COMM port &port->m_ov, // Overlapped structure &BytesSent, // Stores number of bytes sent TRUE); // Wait flag
// deal with the error code if (!bResult) { port->ProcessErrorMessage("GetOverlappedResults() in WriteFile()"); } } // end if (!bWrite)
// Verify that the data size send equals what we tried to send if (BytesSent != strlen((char*)port->m_szWriteBuffer)) { TRACE("WARNING: WriteFile() error.. Bytes Sent: %d; Message Length: %d/n", BytesSent, strlen((char*)port->m_szWriteBuffer)); } }
// start forever loop. I use this type of loop because I // do not know at runtime how many loops this will have to // run. My solution is to start a forever loop and to // break out of it when I have processed all of the // data available. Be careful with this approach and // be sure your loop will exit. // My reasons for this are not as clear in this sample // as it is in my production code, but I have found this // solutiion to be the most efficient way to do this.
if (comstat.cbInQue == 0) { // break out when all bytes have been read break; }
if (bRead) { bResult = ReadFile(port->m_hComm, // Handle to COMM port &RXBuff, // RX Buffer Pointer 1, // Read one byte &BytesRead, // Stores number of bytes read &port->m_ov); // pointer to the m_ov structure // deal with the error code if (!bResult) { switch (dwError = GetLastError()) { case ERROR_IO_PENDING: { // asynchronous i/o is still in progress // Proceed on to GetOverlappedResults(); bRead = FALSE; break; } default: { // Another error has occured. Process this error. port->ProcessErrorMessage("ReadFile()"); break; } } } else { // ReadFile() returned complete. It is not necessary to call GetOverlappedResults() bRead = TRUE; } } // close if (bRead)
if (!bRead) { bRead = TRUE; bResult = GetOverlappedResult(port->m_hComm, // Handle to COMM port &port->m_ov, // Overlapped structure &BytesRead, // Stores number of bytes read TRUE); // Wait flag
// deal with the error code if (!bResult) { port->ProcessErrorMessage("GetOverlappedResults() in ReadFile()"); } } // close if (!bRead)
// notify parent that a byte was received ::SendMessage((port->m_pOwner)->m_hWnd, WM_COMM_RXCHAR, (WPARAM)RXBuff,(LPARAM)port->m_nPortNr); } // end forever loop
}
// // Write a string to the port // void CSerialPort::WriteToPort(char *string) { assert(m_hComm != 0);
