COMMTIMEOUTS

This structure is used in the SetCommTimeouts and GetCommTimeouts functions to set and query the time-out parameters for a communication device. The parameters determine the behavior of the ReadFile and WriteFile function operations on the device.

typedef struct _COMMTIMEOUTS { 
DWORD ReadIntervalTimeout; 
DWORD ReadTotalTimeoutMultiplier; 
DWORD ReadTotalTimeoutConstant; 
DWORD WriteTotalTimeoutMultiplier; 
DWORD WriteTotalTimeoutConstant; 
} COMMTIMEOUTS,*LPCOMMTIMEOUTS; 

Members

• ReadIntervalTimeout
  Specifies the maximum acceptable time, in milliseconds, to elapse between the arrival of two characters on the communication line. During a ReadFile operation, the time period begins when the first character is received. If the interval between the arrival of any two characters exceeds this amount, the ReadFile operation is completed and any buffered data is returned. A value of zero indicates that interval time-outs are not used.

• ReadTotalTimeoutMultiplier
  Specifies the multiplier, in milliseconds, used to calculate the total time-out period for read operations. For each read operation, this value is multiplied by the requested number of bytes to be read.

• ReadTotalTimeoutConstant
  Specifies the constant, in milliseconds, used to calculate the total time-out period for read operations. For each read operation, this value is added to the product of the ReadTotalTimeoutMultiplier member and the requested number of bytes.

  A value of zero for both the ReadTotalTimeoutMultiplier and ReadTotalTimeoutConstant members indicates that total time-outs are not used for read operations.

• WriteTotalTimeoutMultiplier
  Specifies the multiplier, in milliseconds, used to calculate the total time-out period for write operations. For each write operation, this value is multiplied by the number of bytes to be written.

• WriteTotalTimeoutConstant
  Specifies the constant, in milliseconds, used to calculate the total time-out period for write operations. For each write operation, this value is added to the product of the WriteTotalTimeoutMultiplier member and the number of bytes to be written.

  A value of zero for both the WriteTotalTimeoutMultiplier and WriteTotalTimeoutConstant members indicates that total time-outs are not used for write operations.

Remarks

If an application sets ReadIntervalTimeout and ReadTotalTimeoutMultiplier to MAXDWORD and sets ReadTotalTimeoutConstant to a value greater than zero and less than MAXDWORD, one of the following occurs when the ReadFile function is called:

• If there are any characters in the input buffer, ReadFile returns immediately with the characters in the buffer.
• If there are no characters in the input buffer, ReadFile waits until a character arrives and then returns immediately.
• If no characters arrive within the time specified by ReadTotalTimeoutConstant, ReadFile times out.

Requirements

Note   This API is part of the complete Windows CE OS package as provided by Microsoft. The functionality of a particular platform is determined by the original equipment manufacturer (OEM) and some devices may not support this API.

See Also

GetCommTimeouts, ReadFile, SetCommTimeouts, WriteFile

 Last updated on Tuesday, July 13, 2004

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