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POHow do I use COMMTIMEOUTS to wait until bytes are available but read more than one byte?
 

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  1. POHow do I use COMMTIMEOUTS to wait until bytes are available but read more than one byte?
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    <p>I have a C++ serial port class that has a none blocking and a blocking mode for read operations. For blocking mode:</p> <pre><code>COMMTIMEOUTS cto; GetCommTimeouts(m_hFile,&amp;cto); // Set the new timeouts cto.ReadIntervalTimeout = 0; cto.ReadTotalTimeoutConstant = 0; cto.ReadTotalTimeoutMultiplier = 0; SetCommTimeouts(m_hFile,&amp;cto) </code></pre> <p>For non blocking mode:</p> <pre><code>COMMTIMEOUTS cto; GetCommTimeouts(m_hFile,&amp;cto); // Set the new timeouts cto.ReadIntervalTimeout = MAXDWORD; cto.ReadTotalTimeoutConstant = 0; cto.ReadTotalTimeoutMultiplier = 0; SetCommTimeouts(m_hFile,&amp;cto) </code></pre> <p>I would like to add another mode that waits for any number of bytes and read them.</p> <p>From MSDN <a href="http://msdn.microsoft.com/en-us/library/aa363190%28v=vs.85%29.aspx" rel="nofollow">COMMTIMEOUTS structure</a>:</p> <p>If an application sets <strong>ReadIntervalTimeout</strong> and <strong>ReadTotalTimeoutMultiplier</strong> to <strong>MAXDWORD</strong> and sets <strong>ReadTotalTimeoutConstant</strong> to a value greater than zero and less than <strong>MAXDWORD</strong>, one of the following occurs when the ReadFile function is called:</p> <ul> <li>If there are any bytes in the input buffer, ReadFile returns immediately with the bytes in the buffer.</li> <li>If there are no bytes in the input buffer, ReadFile waits until a byte arrives and then returns immediately.</li> <li>If no bytes arrive within the time specified by ReadTotalTimeoutConstant, ReadFile times out.</li> </ul> <p>This looks in code like this:</p> <pre><code>COMMTIMEOUTS cto; GetCommTimeouts(m_hFile,&amp;cto); // Set the new timeouts cto.ReadIntervalTimeout = 100; cto.ReadTotalTimeoutConstant = MAXDWORD; cto.ReadTotalTimeoutMultiplier = MAXDWORD; SetCommTimeouts(m_hFile,&amp;cto) </code></pre> <p>But this returns emidiately on the first byte. This is a problem since I am reading the port in a loop and the handling of a byte is so fast that the next time I read the port, only another byte is available. The end result is that I am reading one byte at a time in a loop and using 100% of the core running that thread.</p> <p>I would like to use the <code>cto.ReadIntervalTimeout</code> like in the MSDN documentation but still wait until at least one byte is available. Does anyone have an idea?</p> <p>Thanks.</p>
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