BBC BASIC for Windows - Opening COM ports -- long delay

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Opening COM ports -- long delay

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g3nrw
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Posts: 74

Opening COM ports -- long delay
« Thread started on: Jul 21^st, 2014, 07:17am »

Here is a simple program that tests the availabilty of a particular COM port once per second:

Code:

      timer% = 100
      t% = 0

      REPEAT
        WAIT 1
        timer% += 1
  
        IF timer% > 100 THEN
    
          t% += 1
          PRINT "                TIME = " + STR$(t%)
    
          timer% = 0
    
          port% = OPENUP("COM4: 115200,N,8,1")
    
          PRINT "port%= " + STR$(port%)
          CLOSE#0
    
        ENDIF
  
      UNTIL FALSE

I have tested this by plugging/unplugging a USB-to-serial adapter into/from the COM4 port on a laptop, running Windows 7/32.

Logically it works OK, but when I plug the adapter into the PC, there is a very long delay (around 4-5 seconds) before the port open state is recognized -- the timer counter update freezes during this time. When I remove the adapter the state is recognized almost immediately.

Is there a way to reduce the OPENUP delay when the port becomes available?

--
Ian

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rtr
Guest

Re: Opening COM ports -- long delay
« Reply #1 on: Jul 21^st, 2014, 08:33am »

on Jul 21^st, 2014, 07:17am, g3nrw wrote:

Is there a way to reduce the OPENUP delay when the port becomes available?

As I'm sure you appreciate, the delay has nothing whatever to do with BBC BASIC, so this isn't really the right forum on which to ask the question.

If you plug in a USB serial adapter Windows has a great deal to do. It must use the plug-and-play mechanism to detect the insertion of the device, identify what sort of device it is, locate and load the appropriate driver, initialise the device, allocate a COM number etc. etc.

It seems unlikely that there will be anything you can do to reduce the delay, but if there is you will need to enquire on an appropriate Windows/USB forum.

Incidentally the subject line "Opening COM ports - long delay" is rather misleading because the delay isn't related to opening the port (which is pretty much instantaneous) but in Windows detecting and installing the USB adaptor.

Richard.

« Last Edit: Jul 21^st, 2014, 08:38am by rtr »

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g3nrw
Junior Member

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Posts: 74

Re: Opening COM ports -- long delay
« Reply #2 on: Jul 21^st, 2014, 10:44am »

Thanks Richard. All understood and regrettably accepted!

--
Ian

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