I sorry I don't have the means to help directly, but I'm curious about a couple things in your "pollForData" sub, and I can suggest a few questions to consider (which you've probably covered already, but hey, no harm asking).

Why do you not check the value of $length? (If you do check that, what do you get?) Why do you check "$buffer eq ''" before you check "!defined $buffer"?

If $length is greater than zero (which means $buffer must be defined), what would you see if you did this before returning:

  printf( "%2.2x ", $_ ) for ( split //, $buffer );
  print "\n";
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(You might want to avoid setting $buffer to the initial value of RED,"NO DATA",RESET -- just set it to undef or "" to start with.)

Since you are doing a non-blocking read on the port, my first guess is that the device is not responding with data, so the original content of $buffer is not being replaced.

Are you using the same host computer (i.e. dual-boot windows/linux), or different boxes? If the latter, are you using the same serial cable on both OS's? (I would always have a null-modem adapter on hand for this kind of thing, and if a device/cable doesn't work without the adapter, I put on the adapter and try again.)