From: Dan Caugherty <dan.caugherty@...>
Date: 2007-08-22T03:19:57+09:00
Subject: Serial port programming

Hey all --

I'm trying to find what seems to be the holy grail of Ruby
programmers: a portable platform-neutral way to access serial ports.
As you'd expect Windows is the most vexing platform to deal with.

I *thought* I could get away with something like the following under
Cygwin (note the default string for opening a Windows serial port).
I'm perfectly happy with opening a port and kicking off a thread to
keep reading data into a buffer every few milliseconds:

  def initialize(filename = "COM1:9600,8,N,1")
    # die horribly if we can't open file for read/write/append

    @mon = Monitor.new
    @buf = ""
    # kick off our collector thread
    @collector = Thread.new(filename) do |fname|
      begin
	if (! (@hdl = open(filename, "w+")))
	  raise "Cannot open for IO"
	end

	loop do
	  if (select([@hdl],nil,nil,0.01))
            if newchars = @hdl.read
	      @mon.synchronize do
		if (0 < newchars.length) then
                  # stick new data into a buffer, let the read method
of the instance read the buffer instead
		  @buf << newchars
		  newchars = nil
		end
	      end
            end
	  end
	end
      rescue
	$stderr.print "#{filename}: IO failed: " + $!
	return
      end
      @hdl.close
    end

    # needed for Cygwin at least
    @collector.wakeup if (@collector && @collector.alive?)
  end

--
The big problem is that even though the select call returns with a
return value indicating that data is waiting, the read call hangs.
Using Fcntl to set the IO instance to use non-blocking IO solves
nothing.

Am I stuck with using the ruby-serialport extension? (And why isn't it
a gem by now anyway? Grr..)


Thanks in advance,
-- Dan