How to do robust SerialPort programming with .NET / C#?

Question

I\'m writing a Windows Service for communication with a Serial Mag-stripe reader and a relay board (access control system).

I run into problems where the code stops

Answer 1

This answer got to long to be a comment...

I believe that when your program is in a Thread.Sleep(1000) and you open your HyperTerminal connection, the HyperTerminal takes control over the serial port. When your program then wakes up and trying to open the serial port, an IOException is thrown.

Redesign your method and try to handle the opening of the port in a different way.

EDIT: About that you have to reboot your computer when your program fails...

That probably because your program isn´t really closed, open your taskmanager and see if you can find your program service. Be sure to stop all your threads before exiting your application.

Answer 2

@thomask

Yes, Hyperterminal does in fact enable fAbortOnError in SetCommState's DCB, which explains for most of the IOExceptions thrown by the SerialPort object. Some PCs / handhelds also have UARTs that have the abort on error flag turned on by default - so it's imperative that a serial port's init routine clears it (which Microsoft neglected to do). I wrote a long article recently to explain this in greater detail (see this if you're interested).

Answer 3

Is there a good reason to keep your service from "owning" the port? Look at the built-in UPS service -- once you tell it there's an UPS attached to, say, COM1, you can kiss that port goodbye. I'd suggest you do the same unless there's a strong operational requirement to share the port.