Windows WaitCommEvent to wait for n characters

Question

I'm trying to set up a uart/serial port in windows. The device I am interfacing to will send me 10 characters and then I need to parse and respond with 30 characters. I need to try and respond in under 2 millseconds.

I plan to use the CreateFile in a synchronous fashion.

I plan to use the following calls

 SetCommMask (hPort, EV_RXCHAR | EV_ERR); //receive character event
 WaitCommEvent (hPort, &dwCommModemStatus, 0); //wait for character 

1. Is there a way to set WaitCommEvent to wait for n characters?
2. Also, do I need to call SetCommMask before every time I call WaitCommEvent? If so, what is the characters come in before I make the call to SetCommMask?
3. One possible solution I'm floating is a combination of event driven with polling until I get the number of characters I need. Is this a good compromise?

Answer 1

The answer is to not use SetCommMask and WaitCommEvent.

I can use SetCommTimeouts, request 10 bytes and set ReadTotalTimeoutConstant to x milliseconds so the call doesn't block forever.

https://learn.microsoft.com/en-us/windows/desktop/api/winbase/ns-winbase-_commtimeouts

if (!::GetCommTimeouts(m_hCommPort, &timeouts))
    std::cout << "error" << std::endl;

timeouts.ReadIntervalTimeout = 0;
timeouts.ReadTotalTimeoutMultiplier = 0;
timeouts.ReadTotalTimeoutConstant = 5000;
timeouts.WriteTotalTimeoutMultiplier = 0;
timeouts.WriteTotalTimeoutConstant = 0;

if (!::SetCommTimeouts(m_hCommPort, &timeouts))
    std::cout << "error" << std::endl;

BYTE Byte;
DWORD dwBytesTransferred;
DWORD dwCommModemStatus;

ReadFile(m_hCommPort, &Byte, 1, &dwBytesTransferred, 0); //read 1