[Edu-sig] Converting from Qbasic

Fred Allen fallen@leveltwo.com
Tue, 7 May 2002 10:16:17 -0700


The available modules supporting serial I/O, to which this thread alludes,
to all seem confined to asynchronous protocols.  Do any among you know of
any available modules supporting synchronous protocols, e.g., binary
synchronous, or bit-synchronous (say HDLC)?

Fred Allen

 -----Original Message-----
From: 	edu-sig-admin@python.org [mailto:edu-sig-admin@python.org]  On Behalf
Of Dethe Elza
Sent:	Tuesday, May 07, 2002 9:34 AM
To:	edu-sig@python.org
Subject:	Re: [Edu-sig] Converting from Qbasic

On Friday, May 3, 2002, at 03:37  PM, Seth David Schoen wrote:

There isn't anything built in to Python which does port I/O.  Doing
port I/O is a low-level and platform-specific operation.  (For
example, it doesn't exist conceptually in Java at all.  It exists on
all PC operating systems, but on Linux and on Windows NT there is a
concept that the user running the code might not be permitted to
perform that operation.)

There may not be any built-in serial I/O in Python (well there is, but
only for Posix, although PyWin gives access to the Windows serial access
methods), but there are plenty of third party solutions, as a quick
google discovered:

Universal Serial Port Python Library (windows/linux)
"Pure Python," wraps existing serial APIs to give a standard interface
http://balder.prohosting.com/ibarona/en/python/uspp/uspp_en.html

Python Serial Port Extension (pySerial: linux/bsd(posix)/windows/jython)
"Pure Python," as above, but more ambitious in scope
http://pyserial.sourceforge.net/

Java also can access serial and parallel ports through the JavaComm API:
http://republika.pl/mho/java/comm/ (links to implementations for many
platforms)

This used to be a much harder problem.  I think Lego Mindstorms inspired
a lot of people to solve it %-)

While Python can give access to serial, parallel, and joystick ports, I
didn't find any standard libaries or APIs for USB or Firewire access.
There were a couple of windows-only USB project, some python info in the
general Linux-USB project, but not much else.  One Japanese page looked
promising, with python info for accessing all kinds of hardware,
including gameboys, etc., but my Japanese was never that good and it
hasn't improved with years of neglect.

The good news is that, if your OS supports these interfaces, there's
probably a way to call native system services to access them.  The bad
news is that they haven't been wrapped in a convenient python API yet.

How can I be so sure there's a way to do it?  On windows there is a
calldll python extension which allows you to, you guessed it, call any
DLL, so the hardest part is finding accurate documentation on assembling
the call.  On Linux everything is treated as a file, so if the kernel
supports serial ports or USB (or whatever) you can generally access it
via Posix calls (same with BSD/OS X and other Posix systems).  On older
MacOS and less common systems (OS/2, BeOS, Amiga, etc.) you may be out
of luck--at least I don't know of any common way to access the hardware
on those systems (BeOS can probably do it through BMessages or
something).

Have fun!

--Dethe

(Seth, sorry about the duplicate, thought I was sending to the list).

--
"Melting down holy grails to make silver bullets for my .357 Panacea"
Dethe Elza (delza@burningtiger.com)
Chief Mad Scientist
Enfolding Systems (http://enfoldingsystems.com)
Weblog: http://livingcode.ca/



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