I’m working in a C/C++ program that communicates with a RS232 device.
The port is opened using CreateFile()
hComm = CreateFile(DevPath, GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, FILE_FLAG_OVERLAPPED, NULL);
Then, the port is Setup using SetupComm(), SetCommState() and SetCommTimeouts() with no hardware control and a baudrate of 115200 baud and timeouts as shown here:
cTimeouts.ReadIntervalTimeout = MAXDWORD; cTimeouts.ReadTotalTimeoutConstant = 1; cTimeouts.ReadTotalTimeoutMultiplier = 0; cTimeouts.WriteTotalTimeoutConstant = 40; cTimeouts.WriteTotalTimeoutMultiplier = 1;
The port is closed using CloseHandle()
This is not a real-time system but has to be very fast, and after noticing some delays I’ve measured that instruction CloseHandle() takes always more than 100ms to run, which is a huge amount of time, taking into account that opening and configuring the port takes only 20ms.
Test conditions are as follows:
- There isn’t any anti-virus or firewall in the test machine (off-line).
- I’m using Visual Studio on an brand-new Intel-based Core-i5 computer, running in Windows 10.
- FTDI USB device (Virtual CommPort)
- There is no data pending to be read or written (or it shouldn’t).
I’ve tried to compile a similar program in Linux and the Close time reduces to 25ms.
I’ve also tried to use a physical RS232 connection and the close times turns to be 1ms, so I presume this comes from the FTDI driver.
Does anyone have any clue on what could be happening. Am I missing anything?
Did anyone experienced something similar?
Source: Windows Questions C++