GetPortNames() returns stale data/Remove stale comport entries in Windows?

1
votes

I'm currently working on a project using the SerialPort class in C# to communicate with RS232-based calibration devices used at the company I work for. In the SerialPort class, there is a static method named GetPortNames().

Unfortunately, Windows has a terrible problem with keeping around stale port entries. If I call GetPortNames() from my machine, it returns the following ports:

COM3
COM4
COM1

Of these ports, only one physically exists right now. I have a PCIe RS232 card on the back of my computer. This is designated COM1.

The other two ports (COM3 and COM4) were created by USB-to-Null Modem cables. These entries still exist in the registry even though the cables have long since been detached (a COM8 existed for some time, but was removed after routinely plugging and unplugging USB cables a few times).

This is okay for me. I can always open up Putty or TeraTerm and check the available COM ports until I find the correct one. This isn't okay for the technicians that will be using this program. I don't know that the COM port will always be the same as they routinely shift USB cables about.

Is there any way (preferably programatically in C#) I can remove these stale entries or, at least, verify which ones are active?

Notes:

From the SerialPort.GetPortNames() MSDN documentation:

Remarks

  • The order of port names returned from GetPortNames is not specified.

  • Use the GetPortNames method to query the current computer for a list of valid serial port names. For example, you can use this method to determine whether COM1 and COM2 are valid serial ports for the current computer.

  • The port names are obtained from the system registry (for example, HKEY_LOCAL_MACHINE\HARDWARE\DEVICEMAP\SERIALCOMM). If the registry contains stale or otherwise incorrect data then the GetPortNames method will return incorrect data.

The following question: Removing COM Ports in Windows programmatically (Setup API ? ) is two years old and unsatisfactory. The only answer (essentialy "Have a look at Program X's source code and try to make something like that") is useless to me.

1
c#windowsserial-portregistry
I would think you could probably simply attempt to open the port (without sending data), and if you get an error, remove it from your own local list. I haven't tried this, but it might work. This might also cause other in-use ports to also disappear, but that just helps narrow down the right one :) – Steve
Windows is not involved at all, it is up to the device driver to write those registry entries. Otherwise standard lossage, the kind of device drivers that emulate a serial port are a very sorry lot. Best way to deal with cranky ones is to uninstall them. – Hans Passant

1 Answers

1
votes

Don't worry about trying to make the computer right. Worry about making sure you connect to the right device. Enumerate the ports then attempt to open and communicate with each one. You should have a handshake / identify type command you can send to the serial device you are trying to connect to. If you get a successful handshake, you know you have a device.