读写CDC类虚拟串口（VCP）跟真实串口有什么不同点么？

68336016 · 发表于昨天 18:36

WIN11， VC2008，多年以来读写串口用一个古董类CSerialPort，不过一直也只是跟原生串口或者USB转串口通信，一直都挺正常的。

改了个上位机要跟STM32的虚拟串口通信，发现不能正常工作，只在打开串口后，才能发送一次数据。要想再次发送，就必须关闭再打开串口。
如果换成USB转的串口，这个上位机是可以正常通信的。
用一些串口调试助手打开这个CDC类虚拟串口，是可以多次发送数据的。

所以问题就是读写这些CDC类虚拟串口，是有什么地方不同，自己没了解到导致的。

#include "stdafx.h"
#include "SerialPort.h"
#include <assert.h>
//
// Constructor
//
CSerialPort::CSerialPort()
{
m_hComm = NULL;
// initialize overlapped structure members to zero
m_ov.Offset = 0;
m_ov.OffsetHigh = 0;
// create events
m_ov.hEvent = NULL;
m_hWriteEvent = NULL;
m_hShutdownEvent = NULL;
m_szWriteBuffer = NULL;
m_nWriteSize = 1;
m_bThreadAlive = FALSE;
memset(m_RxRingBuffer.buffer, 0, sizeof(m_RxRingBuffer.buffer));
m_RxRingBuffer.in = 0;
m_RxRingBuffer.out = 0;
}
//
// Delete dynamic memory
//
CSerialPort::~CSerialPort()
{
do
{
SetEvent(m_hShutdownEvent);
}
while(m_bThreadAlive);
// if the port is still opened: close it
if(m_hComm != NULL)
{
CloseHandle(m_hComm);
m_hComm = NULL;
}
// Close Handles
if(m_hShutdownEvent != NULL)
CloseHandle(m_hShutdownEvent);
if(m_ov.hEvent != NULL)
CloseHandle(m_ov.hEvent);
if(m_hWriteEvent != NULL)
CloseHandle(m_hWriteEvent);
TRACE("Thread ended\n");
delete [] m_szWriteBuffer;
}
//
// Initialize the port. This can be port 1 to 4.
//
BOOL CSerialPort::InitPort(CWnd* pPortOwner, // the owner (CWnd) of the port (receives message)
UINT portnr, // portnumber (1..4)
UINT baud, // baudrate
char parity, // parity
UINT databits, // databits
UINT stopbits, // stopbits
DWORD dwCommEvents, // EV_RXCHAR, EV_CTS etc
UINT writebuffersize) // size to the writebuffer
{
assert(portnr > 0 && portnr < 255);
assert(pPortOwner != NULL);
// if the thread is alive: Kill
if(m_bThreadAlive)
{
do
{
SetEvent(m_hShutdownEvent);
}
while(m_bThreadAlive);
TRACE("Thread ended\n");
}
// create events
if(m_ov.hEvent != NULL)
ResetEvent(m_ov.hEvent);
else
m_ov.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
if(m_hWriteEvent != NULL)
ResetEvent(m_hWriteEvent);
else
m_hWriteEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
if(m_hShutdownEvent != NULL)
ResetEvent(m_hShutdownEvent);
else
m_hShutdownEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
// initialize the event objects
m_hEventArray[0] = m_hShutdownEvent; // highest priority
m_hEventArray[1] = m_ov.hEvent;
m_hEventArray[2] = m_hWriteEvent;
// initialize critical section
InitializeCriticalSection(&m_csCommunicationSync);
// set buffersize for writing and save the owner
m_pOwner = pPortOwner;
if(m_szWriteBuffer != NULL)
delete [] m_szWriteBuffer;
m_szWriteBuffer = new char[writebuffersize];
m_nPortNr = portnr;
m_nWriteBufferSize = writebuffersize;
m_dwCommEvents = dwCommEvents;
BOOL bResult = FALSE;
char *szPort = new char[50];
char *szBaud = new char[50];
// now it critical!
EnterCriticalSection(&m_csCommunicationSync);
// if the port is already opened: close it
if(m_hComm != NULL)
{
CloseHandle(m_hComm);
m_hComm = NULL;
}
// prepare port strings
sprintf(szPort, "\\\\.\\COM%d", portnr);
sprintf(szBaud, "baud=%d parity=%c data=%d stop=%d", baud, parity, databits, stopbits);
// 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.EvtChar = 'q';
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()");
////设置超大接收缓冲区
//SetupComm(m_hComm, 200000, 1024);
delete [] szPort;
delete [] szBaud;
// flush the port
PurgeComm(m_hComm, PURGE_RXCLEAR | PURGE_TXCLEAR | PURGE_RXABORT | PURGE_TXABORT);
// release critical section
LeaveCriticalSection(&m_csCommunicationSync);
TRACE("Initialisation for communicationport %d completed.\nUse Startmonitor to communicate.\n", portnr);
return TRUE;
}
//
// The CommThread Function.
//
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;
// Misc. variables
DWORD BytesTransfered = 0;
DWORD Event = 0;
DWORD CommEvent = 0;
DWORD dwError = 0;
COMSTAT comstat;
BOOL bResult = 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);
// Initialize comstat
ClearCommError(port->m_hComm, &dwError, &comstat);
// 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.
// we do this for each port!
bResult = WaitCommEvent(port->m_hComm, &Event, &port->m_ov);
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.
bResult = ClearCommError(port->m_hComm, &dwError, &comstat);
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.
CloseHandle(port->m_hComm);
port->m_hComm = NULL;
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_RXCHAR)
// Receive character event from port.
ReceiveChar(port, comstat);
if(CommEvent & EV_CTS)
::SendMessage(port->m_pOwner->m_hWnd, WM_COMM_CTS_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_RXFLAG)
::SendMessage(port->m_pOwner->m_hWnd, WM_COMM_RXFLAG_DETECTED, (WPARAM) 0, (LPARAM) port->m_nPortNr);
break;
}
case 2: // write event
{
// Write character event from port
WriteChar(port);
break;
}
} // end switch
} // close forever loop
return 0;
}
//
// start comm watching
//
BOOL CSerialPort::StartMonitoring()
{
if(!(m_Thread = AfxBeginThread(CommThread, this)))
return FALSE;
TRACE("Thread started\n");
return TRUE;
}
//
// Restart the comm thread
//
BOOL CSerialPort::RestartMonitoring()
{
TRACE("Thread resumed\n");
m_Thread->ResumeThread();
return TRUE;
}
//
// Suspend the comm thread
//
BOOL CSerialPort::StopMonitoring()
{
TRACE("Thread suspended\n");
m_Thread->SuspendThread();
return TRUE;
}
//
// If there is a error, give the right message
//
void CSerialPort::ProcessErrorMessage(char* ErrorText)
{
char *Temp = new char[200];
LPVOID lpMsgBuf;
FormatMessage(
FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM,
NULL,
GetLastError(),
MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), // Default language
(LPTSTR) &lpMsgBuf,
0,
NULL
);
sprintf(Temp, "WARNING: %s Failed with the following error: \n%s\nPort: %d\n", (char*)ErrorText, lpMsgBuf, m_nPortNr);
MessageBox(NULL, Temp, "Application Error", MB_ICONSTOP);
LocalFree(lpMsgBuf);
delete [] Temp;
}
//
// Write a character.
//
void CSerialPort::WriteChar(CSerialPort* port)
{
BOOL bWrite = TRUE;
BOOL bResult = TRUE;
DWORD BytesSent = 0;
ResetEvent(port->m_hWriteEvent);
// Gain ownership of the critical section
EnterCriticalSection(&port->m_csCommunicationSync);
if(bWrite)
{
// Initailize variables
port->m_ov.Offset = 0;
port->m_ov.OffsetHigh = 0;
// Clear buffer
PurgeComm(port->m_hComm, PURGE_RXCLEAR | PURGE_TXCLEAR | PURGE_RXABORT | PURGE_TXABORT);
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
port->m_nWriteSize, // 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
LeaveCriticalSection(&port->m_csCommunicationSync);
// 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 != port->m_nWriteSize) // Length of message to send)
{
TRACE("WARNING: WriteFile() error.. Bytes Sent: %d; Message Length: %d\n", BytesSent, strlen((char*)port->m_szWriteBuffer));
}
// ::SendMessage((port->m_pOwner)->m_hWnd, WM_COMM_TXEMPTY_DETECTED, (WPARAM) RXBuff, (LPARAM) port->m_nPortNr);
// ::SendMessage((port->m_pOwner)->m_hWnd, WM_COMM_TXEMPTY_DETECTED,0,(LPARAM) port->m_nPortNr);
}
//
// Character received. Inform the owner
void CSerialPort::ReceiveChar(CSerialPort * port, COMSTAT comstat)
{
BOOL bRead = TRUE;
BOOL bResult = TRUE;
DWORD dwError = 0;
DWORD BytesRead = 0;
const int bufferSize = 1024; // 定义缓冲区大小
unsigned char RXBuff[bufferSize]; // 定义缓冲区
for(;;)
{
EnterCriticalSection(&port->m_csCommunicationSync);
bResult = ClearCommError(port->m_hComm, &dwError, &comstat);
LeaveCriticalSection(&port->m_csCommunicationSync);
if(comstat.cbInQue == 0)
{
break;
}
EnterCriticalSection(&port->m_csCommunicationSync);
if(bRead)
{
bResult = ReadFile(port->m_hComm, // Handle to COMM port
RXBuff, // RX Buffer Pointer
bufferSize, // Read bufferSize bytes
&BytesRead, // Stores number of bytes read
&port->m_ov); // pointer to the m_ov structure
if(!bResult)
{
switch(dwError = GetLastError())
{
case ERROR_IO_PENDING:
bRead = FALSE;
break;
default:
port->ProcessErrorMessage("ReadFile()");
break;
}
}
else
{
bRead = TRUE;
}
}
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
if(!bResult)
{
port->ProcessErrorMessage("GetOverlappedResults() in ReadFile()");
}
}
LeaveCriticalSection(&port->m_csCommunicationSync);
for(DWORD i = 0; i < BytesRead; ++i)
{
port->m_RxRingBuffer.buffer[port->m_RxRingBuffer.in++] = RXBuff[i];
if(port->m_RxRingBuffer.in >= MAX_RING_LEN)
{
port->m_RxRingBuffer.in = 0;
}
} // end forever loop
::PostMessage((port->m_pOwner)->m_hWnd, WM_COMM_RXCHAR, 1, (LPARAM) port->m_nPortNr);
}
}
//
// Write a string to the port
//
void CSerialPort::WriteToPort(char * string)
{
assert(m_hComm != 0);
memset(m_szWriteBuffer, 0, sizeof(m_szWriteBuffer));
strcpy(m_szWriteBuffer, string);
m_nWriteSize = strlen(string);
// set event for write
SetEvent(m_hWriteEvent);
}
void CSerialPort::WriteToPort(char * string, int n)
{
assert(m_hComm != 0);
memset(m_szWriteBuffer, 0, sizeof(m_szWriteBuffer));
// memset(m_szWriteBuffer, 0, n);
// strncpy(m_szWriteBuffer, string, n);
memcpy(m_szWriteBuffer, string, n);
m_nWriteSize = n;
// set event for write
SetEvent(m_hWriteEvent);
}
void CSerialPort::WriteToPort(LPCTSTR string)
{
assert(m_hComm != 0);
memset(m_szWriteBuffer, 0, sizeof(m_szWriteBuffer));
strcpy(m_szWriteBuffer, string);
m_nWriteSize = strlen(string);
// set event for write
SetEvent(m_hWriteEvent);
}
void CSerialPort::WriteToPort(LPCTSTR string, int n)
{
assert(m_hComm != 0);
memset(m_szWriteBuffer, 0, sizeof(m_szWriteBuffer));
// strncpy(m_szWriteBuffer, string, n);
memcpy(m_szWriteBuffer, string, n);
m_nWriteSize = n;
// set event for write
SetEvent(m_hWriteEvent);
}
//
// Return the device control block
//
DCB CSerialPort::GetDCB()
{
return m_dcb;
}
//
// Return the communication event masks
//
DWORD CSerialPort::GetCommEvents()
{
return m_dwCommEvents;
}
//
// Return the output buffer size
//
DWORD CSerialPort::GetWriteBufferSize()
{
return m_nWriteBufferSize;
}
void CSerialPort::ClosePort()
{
SetEvent(m_hShutdownEvent);
}
void CSerialPort::ProcessData(void)
{
}
/*
void CSerialPort::ClosePort()
{
do
{
SetEvent(m_hShutdownEvent);
} while (m_bThreadAlive);
// if the port is still opened: close it
if (m_hComm != NULL)
{
CloseHandle(m_hComm);
m_hComm = NULL;
}
// Close Handles
if(m_hShutdownEvent!=NULL)
CloseHandle( m_hShutdownEvent);
if(m_ov.hEvent!=NULL)
CloseHandle( m_ov.hEvent );
if(m_hWriteEvent!=NULL)
CloseHandle( m_hWriteEvent );
TRACE("Thread ended\n");
delete [] m_szWriteBuffer;
}
*/

复制代码

68336016 · 发表于昨天 19:04

估计代码不够严谨，问了下人工智能助手Copilot，
帮我改了发送函数，这下发送正常了。

t3486784401 · 发表于昨天 20:50

bushound 试试看哪里卡住了？

CDC 本来就是标准的抽象设备，不该跑不通

tuy0326 · 发表于昨天 21:19

震惊到了
Copilot都能改代码了？
而且这个代码不是玩具。
那么，问题来了
你是怎么问的Copilot呢？

68336016 · 发表于昨天 21:51

t3486784401 发表于 2024-7-26 20:50
bushound 试试看哪里卡住了？

CDC 本来就是标准的抽象设备，不该跑不通
(引用自3楼)

我软件调试能力不行啊，看原先代码也是调用WriteChar的，里面也是异步方式。
Copilot给我改的代码只是一个函数完成了发送，跟通过事件然后调用WriteChar区别好像也不大。
我也试着将WriteChar里面代码改成跟Copilot的一样方式，能在Serial Port Monitor看到有往下位机发送的字符，但是实际下位机并没有收到。
所以我也判断不出什么问题了。
我随时切换串口助手，发送一个字符到下位机，下位机是随时能响应的，所以下位机是没什么问题的，这个发送的字符就是有时监控软件看着发下来了，实际没有收到。

68336016 · 发表于昨天 21:54

tuy0326 发表于 2024-7-26 21:19
震惊到了
Copilot都能改代码了？
而且这个代码不是玩具。
(引用自4楼)

我就把函数发给Copilot，告诉他这函数有时无法发送成功，他自己就懂事去修改了

真不是玩具，完全就是生产力工具

t3486784401 · 发表于昨天 22:17

68336016 发表于 2024-7-26 21:51
我软件调试能力不行啊，看原先代码也是调用WriteChar的，里面也是异步方式。
Copilot给我改的代码只是一 ...
(引用自5楼)

win32 下边是以文件的方式访问 CDC 串口的，楼主位这个串口类不知是否也用到了这一层 API：

::CreateFile 就是打开串口， ::CloseFile 就是关闭串口；
::WriteFile 就是发送，::ReadFile 对应接收。

以前最早做串口的时候，用的是 mscomm32；后来这控件又是限制数目又是新系统不兼容的，索性全换了 Win32-API 方式。
然后就舒坦了，从 XP 一直到 win10 都兼容，而且不需额外安装插件

读写CDC类虚拟串口（VCP）跟真实串口有什么不同点么？

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阿莫论坛20周年了！感谢大家的支持与爱护！！

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