Destroying tied serial port

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

Greetings, Perl monks:

I'm developing an application which communicates with an Arduino via USB. It runs in a POE environment. I use the Device::SerialPort module to talk to the USB port (as a file).

At times I want to close the connection (when certain errors occur) and re-open it. So far, closing the connection is not working for me. Here's how I open it:

use Symbol qw(gensym);
use Device::SerialPort;
(etc.)
my $port, $handle;
$handle = gensym();
$port = tie(*$handle, "Device::SerialPort", "/dev/ttyUSB0");
$port->baudrate(57600);
(etc.)
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By passing $handle to a POE ReadWrite wheel, I can communicate perfectly with the Arduino. I use the following code to try to close the connection, prior to re-opening it:

$port->close;
undef $port;
untie *$handle;
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and this results in the error message:

<fh> select error: Bad file descriptor (hits=-1)
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I have to admit that I don't understand what the "gensym" and "tie" stuff is all about; I'm just following the examples in the documentation, so it's almost certainly due to my ignorance. Can anyone explain how to properly close this port?

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Re: Destroying tied serial port by Marais (Novice) on Dec 23, 2012 at 22:00 UTC
It's embarrassing how often the simple act of documenting your problem leads you to find the cause. In this case, I had a variable ($handle) defined both locally and globally - an old, old story. Fixing that did get me past the problem I described above, not surprisingly. Now of course there is another problem, but I'll consider that one myself a little more before asking for help. --- Marais	[reply]
Re^2: Destroying tied serial port by roboticus (Chancellor) on Dec 24, 2012 at 00:03 UTC
Marais: It's not embarrassing at all. In fact it's an old and quite valuable debugging technique. That's why I frequently create a simple 'test case' program to try to illustrate a bug. The act often helps you understand what's going on, and can point out interactions with other parts of your program. It's also the reason that we frequently ask for a simple program that illustrates the problem. The act of doing that can help you answer the question yourself, which is a faster way to learn how to code. (It's also the reason I like Test Driven Development (TDD), as it's a similar (in some ways) process.) ...roboticus When your only tool is a hammer, all problems look like your thumb.	[reply]
Re: Destroying tied serial port by jmlynesjr (Deacon) on Dec 24, 2012 at 02:23 UTC
Also take a look at Device::SerialPort::Arduino. I'm using that to talk to a chipKIT UNO. Maybe something in the code will help you out. James There's never enough time to do it right, but always enough time to do it over...	[reply]