pashanoid has asked for the wisdom of the Perl Monks concerning the following question:

Dear Bretheren, is there a way to poll/find a working serial port in the system without crashing it? My Linux setup works just fine, however, once I'm on Win32 everything crashes!? 

sub connect{
  if ($os =~ /Win/i){ #this only works with COM1
    my @ports_win = ('COM1');
       foreach (@ports_win){
           open_uart($_);
           last if ($PortObj);
       }
   } else { #This works great
      my @ports = ('/dev/ttyUSB0','/dev/ttyUSB1','/dev/ttyUSB2','/dev/
+ttyUSB3','/dev/ttyUSB4','/dev/ttyUSB5','/dev/ttyUSB6');
   foreach (@ports){
      open_uart($_);
      last if ($PortObj);
    } 
  }
 }
}

sub open_uart {

        $port_to_open = shift;
        &attempt($port_to_open);
        if ($port_not_opening){ #try to connect!
                for (my $i=1; $i<=15; $i++){
                        &attempt($port_to_open);
                        print "trying to connect $i\n";
                        last unless ($port_not_opening);
                }
        }



        return if ($port_not_opening);
        $PortObj->is_rs232;
        $PortObj->handshake("none");
        $PortObj->user_msg(1);
        $PortObj->baudrate($conn_speed);
        $PortObj->parity("none");
        $PortObj->databits(8);
        $PortObj->stopbits(1);
        $PortObj->read_const_time(500);       # 500 milliseconds = 0.5
+ seconds
        $PortObj->read_char_time(500);       #was 5   # avg time betwe
+en read char
        $PortObj->buffers(4096, 4096);  # read, write
        $PortObj->parity_enable(1);
        $PortObj->write_settings || undef $PortObj;
        #print "Can't change Device_Control_Block: $^E\n" unless ($Por
+tObj);
}

sub attempt {
        $port_to_open = shift;
        $port_not_opening ="";
        if ($os =~ /Win/i){ #win32
                eval {
                        $PortObj = new Win32::SerialPort ($port_to_ope
+n) or $port_not_opening = $port_to_open;
                };
        } else { #linux
                eval {
                        $PortObj = new Device::SerialPort ("$port_to_o
+pen") or $port_not_opening = $port_to_open;
                };
        }

}

[download]

Replies are listed 'Best First'.
Re: finding a serial port with Win32::SerialPort
by Marshall (Canon) on Aug 22, 2011 at 10:20 UTC
    Well this dog just doesn't hunt.
    I don't see any code that searches for a COM port. 
    sub connect
{
   if ($os =~ /Win/i)
   {
      #this only works with COM1 ? Huh?
      # my @ports_win = ('COM1');
      foreach ('COM1') #same as foreach (@ports_win){}
      {
         open_uart($_);
      } 
   }
}

    [download]
[reply]
[d/l]
      Yes, because my @ports_win = ('COM5', 'COM4','COM1', 'COM2',); crashes a win32 system
[reply]
        Yes, using the code from AnonMonk...

        You have to ask Win32 what the names of the COM ports are or probe up to a certain COMxx number.

        There are USB ports that can show up as COM ports and I don't know how to create a complete list. I think its hard to do because a new COM port can just "show up" dynamically (i.e. when you plug in a new USB device).

        This may not be right, but this is what it does on my machine.

        #!/usr/bin/perl -w
use strict;
use Data::Dumper;

use Win32::SerialPort;
use Win32::OLE('in');
use constant wbemFlagReturnImmediately => 0x10;
use constant wbemFlagForwardOnly => 0x20;

my $computer = ".";

my $objWMIService = Win32::OLE->GetObject
    ("winmgmts:\\\\$computer\\root\\CIMV2") 
    or die "WMI connection failed.\n";
    
my $colItems = $objWMIService->ExecQuery
    ("SELECT * FROM Win32_SerialPortConfiguration",
     "WQL",wbemFlagReturnImmediately | wbemFlagForwardOnly);

foreach my $objItem (in $colItems)
{
    print "Caption: $objItem->{Caption}\n";
    print "Name: $objItem->{Name}\n";
}
__END__
prints:
Caption: COM1
Name: COM1

        [download]
        I think perhaps another possibility is to "probe COM ports". Use a block "eval" on the "open_uart($_);" statement. >br> Run through the first 32 ports. If a port works works then $_ is a valid COM port and push it onto some stack.

        my @valid_com_ports;
foreach my $com ( map{"COM$_"}1..32)
{
   # decide if this $com is ok or not..
   # perhaps use the open_uart function()
   # and then push @valid_com_ports, $com;
}

        [download]
[reply]
[d/l]
[select]
[reply]
Re: finding a serial port with Win32::SerialPort
by ajose (Acolyte) on Aug 25, 2011 at 18:58 UTC

    I think you should try Hardware::PortScanner for scanning the active COM ports. This works for both Win32 and *nix.

[reply]

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