From: Brian Candler <B.Candler@...>
Date: 2004-10-04T17:23:42+09:00
Subject: Re: Reinventing Telnet Servers for Serial Ports

On Sun, Oct 03, 2004 at 01:24:47PM +0900, Siegfried Heintze wrote:
> How can I write a similar OS vendor neutral program using ruby,
> except, instead reading and writing to a process, I read and write to
> serial port? Can I do this with a single thread? How do I read and
> write to a serial port? Can anyone point me to some sample code for
> serial port I/O? 

The module ruby-termios from RAA has examples of serial port I/O, and how to
set things like the bit rate and start/stop bits.

Beware: if you are using Linux, there is a serious bug with serial I/O and
Ruby, which means that I/O blocks when it shouldn't. I reported this on
ruby-talk and ruby-core, but nothing happened:

http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/111331
http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/111330

http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-core/3366

It works fine under FreeBSD though, so conceivably it's a Linux kernel
problem.

As for threads etc: it depends on the application. If you're copying data to
a socket or to another process on stdin/stdout, then I'd use one thread to
read and another to write. Ruby threads are simulated threads, using
select() to determine when an FD is ready to read or write. That's as long
as you don't get bitten by the thread/serial port bug above, of course.

Regards,

Brian.