串口发送数据出现停顿的问题

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    你好！我贴上打开串口和发送数据的函数，请你帮忙看一看。

//打开串口
/****************************************************************************\\
*
* name Open_ComPort
*
*           Opens the specified COM-Port with the specified Baudrate.
* Communication parameter: 8 databits, 1 stopbit, no parity
*
* Inputs    ComStr  ... possible: \"COM1\", \"COM2\", \"COM3\", \"COM4\"
* BaudStr ... possible: \"115200L\", \"57600L\", \"38400L\", \"28800L\",
*  \"19200L\", \"14400L\", \"9600L\"
*
* Return MI_INITERR, 0 ... 3 (Handle for COM1 ... COM4)
*
\\****************************************************************************/
int __stdcall Open_ComPort (unsigned __int16 ComStr, unsigned __int16 BaudStr)
{
// int base;
DWORD dwError;
DCB dcb;
// char buf[80];
uchar sbuf;
int e;
LPCTSTR m_sPort;
unsigned int ComInt=ComStr;


COMMTIMEOUTS TimeOuts;
e=0;
sbuf=0;
switch (ComInt)
{
case 0:
m_sPort=\"COM1\";
break;
case 1:
m_sPort=\"COM2\";
break;
case 2:
m_sPort=\"COM3\";
break;
case 3:
m_sPort=\"COM4\";
break;
default:                 // baudrate not supported

return(MI_INITERR);
}


m_hCom=CreateFile(m_sPort, GENERIC_READ | GENERIC_WRITE, 0, NULL,
OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL | FILE_FLAG_OVERLAPPED,NULL); // 重叠方式
/*
m_hCom=CreateFile(m_sPort, // Pointer to the name of the port
GENERIC_READ | GENERIC_WRITE, // Access (read/write) mode
0, // Share mode
NULL, // Pointer to the security attribute
        OPEN_EXISTING, // How to open the serial port
0, // Port attributes
NULL); // 重叠方式// Handle to port with attribute to copy
*/
if(m_hCom==INVALID_HANDLE_VALUE)//检测打开串口操作是否成功
{
dwError = GetLastError ();
return(MI_INITERR);
}

SetupComm(m_hCom,INMAXBLOCK,OUTMAXBLOCK);//设置输入、输出缓冲区的大小

SetCommMask(m_hCom, EV_RXCHAR | EV_TXEMPTY);//设置事件驱动的类型

PurgeComm( m_hCom, PURGE_TXABORT | PURGE_RXABORT | PURGE_TXCLEAR | PURGE_RXCLEAR ); //清干净输入、输出缓冲区


// Retrieve the time-out parameters for all read and write operations
  // on the port.
GetCommTimeouts (m_hCom, &TimeOuts);
// 把间隔超时设为最大，把总超时设为0将导致ReadFile立即返回并完成操作
TimeOuts.ReadIntervalTimeout=MAXDWORD;
TimeOuts.ReadTotalTimeoutMultiplier=0;
TimeOuts.ReadTotalTimeoutConstant=0;
/* 设置写超时以指定WriteComm成员函数中的
GetOverlappedResult函数的等待时间*/
TimeOuts.WriteTotalTimeoutMultiplier=50;
TimeOuts.WriteTotalTimeoutConstant=2000;
SetCommTimeouts(m_hCom, &TimeOuts);

dcb.DCBlength = sizeof (DCB);
 // Get the default port setting information.
if(!GetCommState(m_hCom, &dcb))
{
dwError = GetLastError ();
CloseHandle(m_hCom);
return(MI_INITERR);
}

// Change the DCB structure settings.
dcb.fBinary=TRUE; // Binary mode; no EOF check
// dcb.BaudRate=1200;//m_nBaud; // 波特率 // Current baud
dcb.ByteSize=8;//m_nDataBits; // 每字节位数// Number of bits/bytes, 4-8
dcb.fParity=TRUE; // Enable parity checking.
dcb.Parity=NOPARITY; // 0-4=no,odd,even,mark,space
dcb.StopBits=ONESTOPBIT; // 0,1,2 = 1, 1.5, 2


dcb.fOutxCtsFlow = FALSE;         // No CTS output flow control
dcb.fOutxDsrFlow = FALSE;         // No DSR output flow control
dcb.fDtrControl = DTR_CONTROL_ENABLE;
                                        // DTR flow control type
dcb.fDsrSensitivity = FALSE;      // DSR sensitivity
dcb.fTXContinueOnXoff = TRUE;     // XOFF continues Tx
dcb.fOutX = FALSE;                // No XON/XOFF out flow control
dcb.fInX = FALSE;                 // No XON/XOFF in flow control
dcb.fErrorChar = FALSE;           // Disable error replacement.
dcb.fNull = FALSE;                // Disable null stripping.
dcb.fRtsControl = RTS_CONTROL_ENABLE; // RTS flow control
dcb.fAbortOnError = FALSE;        // Do not abort reads/writes on error.


MIFS_Baud = BaudStr;

switch (MIFS_Baud)
{
case 300L:
dcb.BaudRate = CBR_300; // set baudrate via DCB-structure
break;
case 600L:
dcb.BaudRate = CBR_600; // set baudrate via DCB-structure
break;

case 1200L:
dcb.BaudRate = CBR_1200; // set baudrate via DCB-structure
break;

case 2400L:
dcb.BaudRate = CBR_2400; // set baudrate via DCB-structure
break;

case 4800L:
dcb.BaudRate = CBR_4800; // set baudrate via DCB-structure
break;
case 9600L:
dcb.BaudRate = CBR_9600; // set baudrate via DCB-structure
break;

case 19200L:
dcb.BaudRate = CBR_19200; // set baudrate via DCB-structure
break;

case 14400L:
dcb.BaudRate = CBR_14400; // set baudrate via DCB-structure
break;

case 38400L:
dcb.BaudRate = CBR_38400; // set baudrate via DCB-structure
break;

case  56000L:
dcb.BaudRate = CBR_56000; // set baudrate via DCB-structure
break;
//case  28800L:
case  57600L:
dcb.BaudRate = CBR_57600; // set baudrate via DCB-structure
break;

case 115200L:
dcb.BaudRate = CBR_115200; // set baudrate via DCB-structure
break;

default:                 // baudrate not supported
CloseHandle(m_hCom);
return(MI_INITERR);
}

if (SetCommState(m_hCom,&dcb) < 0)
{
dwError = GetLastError ();
CloseHandle(m_hCom);
return (MI_INITERR);
}

BCCMode = SER_BCC; // default
ChkBytes = BCC_CHKBYTES; // default
CHeckMode=CHecksum_1Byte;

return (int(m_hCom));//(CMD_OK);
}

//发送数据
/****************************************************************************\\
*
* name send_char
*
*           transmits one character via API
*
* Inputs c ... character to transmit
*
* Return    CMD_OK, MI_SERERR
*
\\****************************************************************************/

__int16 send_char (uchar *c,uchar slength)
{
BOOL fState;
DWORD length=slength;
COMSTAT ComStat;
DWORD dwErrorFlags;

ClearCommError(m_hCom,&dwErrorFlags,&ComStat);
fState=WriteFile(m_hCom,c,length,&length,&m_osWrite);
// fState=WriteFile(m_hCom,c,length,&length,NULL);
// dwErrorFlags = GetLastError ();

if(!fState)
{
if(GetLastError()==ERROR_IO_PENDING)
GetOverlappedResult(m_hCom,&m_osWrite,&length,TRUE);// 等待
else
return (MI_SERERR);
}

return (CMD_OK);
}