newbie socket help
jldunn2000 at gmail.com
Mon Feb 6 10:23:41 CET 2012
OS is Red hat enterprise linux 5.5 and python version is 2.6
On Feb 2, 4:34 pm, Dennis Lee Bieber <wlfr... at ix.netcom.com> wrote:
> On Thu, 2 Feb 2012 05:53:22 -0800 (PST), loial <jldunn2... at gmail.com>
> >I am trying to write a python script to read data from a printer port
> >using python sockets, but it seems I am locking up the port.
> >Is there a way to ensure that I do not block the port to other
> >My knowledge of python sockets is minimal, so any help would be
> OS and Python version might be of interest...
> However, parallel ports are typically unshared devices (which is why
> any multitasking system has things like print spooling -- so multiple
> tasks and "print" to the spool, and the spool driver is the only process
> actually accessing the printer port).
> I still have nightmares over one assignment I had some 8 years ago:
> Reading a clock signal (square wave) on one of the parallel port's
> signal pins, in order to time a three-bit /balanced/ (using 6-pins of
> the output) data stream. Done on a W98 laptop (since W98 didn't have the
> protected ports of WinXP) using Visual C++ -- and on the laptop as the
> eventual plan had been to send "red" GPS decryption keys to satellites;
> contact with "red" keys makes the hardware it passes through highly
> classified, and the main hardware had to stay "open" for uncleared
> developers working on flight software.
> Unfortunately, even with the program running at the highest
> available Windows priority, the OS still did <something> every few
> milliseconds, which led to glitches in the output stream. (The good
> news: by the time the DTD with the keys became available, the CONOPS had
> changed to use "black" keys, which did not "infect" the computer system
> -- so the regular command formatter could be used for uploading).
> Wulfraed Dennis Lee Bieber AF6VN
> wlfr... at ix.netcom.com HTTP://wlfraed.home.netcom.com/
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