BBC BASIC for Windows - Identifying non-existent COM ports?

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Identifying non-existent COM ports?

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Topic: Identifying non-existent COM ports? (Read 1379 times)

g3nrw
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Posts: 74

Re: Identifying non-existent COM ports?
« Reply #4 on: Oct 4^th, 2014, 12:55pm »

Using GetLastError:

Code:

      FOR p% = 1 TO 255
        port% = OPENIN("COM" + STR$(p%)  + ": 115200,N,8,1")
        SYS "GetLastError" TO winerr%
  
        CASE winerr% OF
          WHEN 0:
            PRINT "COM" + STR$(p%) + "  Free"
            CLOSE# port%
      
          WHEN 1:
            PRINT "COM" + STR$(p%) + "  In Use"
      
        ENDCASE
  
      NEXT

This works OK, but only for port name values "COMn" (this includes VSPE ports).

If com0com is in use, you have no idea how the port name values are defined -- the user can specify any value -- so the above code won't work.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Re WMI, http://bb4w.wikispaces.com/Enumerating+serial+ports , I tried that. Strangely, it only enumerates the com0com ports (but doesn't do this properly), and ignores COM ports altogether! (This is under Windows 7/32).

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

So the only accurate source of port name values that I can find is in the registry. Problem now is discovering the names, so I can then retrieve the values.

--
Ian

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rtr2
Guest

Re: Identifying non-existent COM ports?
« Reply #5 on: Oct 4^th, 2014, 2:06pm »

on Oct 4^th, 2014, 12:55pm, g3nrw wrote:

Strangely, it only enumerates the com0com ports (but doesn't do this properly), and ignores COM ports altogether! (This is under Windows 7/32).

To reiterate, that is the official method for enumerating serial ports in Windows. If it is not returning the port(s) in which you are interested your system is broken and you cannot expect anything to work correctly.

Quote:

So the only accurate source of port name values that I can find is in the registry.

It isn't legitimate to read the registry directly - it is a hack which is not guaranteed to work on different versions of Windows. You should fix the cause of the WMI problem, not attempt to work around it.

My guess would be that COM0COM is broken; I would suggest that you try using Virtual Null Modem instead. That's the utility I use and I have not noticed it causing any unexpected behaviour:

http://www.virtual-null-modem.com/

Richard.

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