# Serial port programming

**URL:** <https://www.ruby-forum.com/t/serial-port-programming/112648>\
**Category:** Ruby\
**Created:** [August 21, 2007, 8:20pm UTC](https://www.ruby-forum.com/t/serial-port-programming/112648 "2007-08-21T20:20:35Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![thechak](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/aeb1de/32.png) [@thechak](https://www.ruby-forum.com/u/thechak)\
**Post date:** [August 21, 2007, 8:20pm UTC](https://www.ruby-forum.com/t/serial-port-programming/112648/1 "2007-08-21T20:20:35Z")

</div>

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