Com port interrupts again

Peter Hansen peter at
Fri Jan 14 23:25:21 EST 2005

engsol wrote:
> I didn't fully think through my application before posting my
> question. Async com port routines to handle com port interrups
> only work well if one has access to the low level operating
> system. In that case the receive buffer interrupt would cause
> a jump to an interrupt service routine.. I don't believe that
> Python provides that capabilty directly. The solution then would
> be to write a C extention?

Maybe, but I doubt that you can or would really want to do this
with modern operating systems anyway.  With DOS, and similar
primitive things, glomming onto an interrupt or hooking yourself
into the interrupt table was pretty easy.  I don't think either
Windows or Linux is structured such that you just "write a
C extension" to intercept interrupts.  Instead, you must write
relatively complicated drivers which have to be loaded at
system startup (more or less) and be tied into the kernel at
a relatively low level.  Think "rocket science", at least in
comparison to writing a simple C extension. :-)

> The suggestions offered by respondents to my original post
> were almost all of a "Use threads, and poll as needed" flavor.
> You're right...I need to learn threads as applied to com ports.

At least on Windows, I'm fairly sure you can configure the
read timeouts so that you get behaviour on reads that for
all intents and purposes is about as good as an interrupt,
without the difficulties inherent in that approach, but
provided you are willing to dedicate a thread to the task.

On Linux, it's possible the read timeouts capabilities are
a little less flexible (but I've only just barely glanced
at this area), but as I recall you were on Windows anyway.

BTW, another post pointed you to USPP.  As far as I know,
it hasn't been updated recently and, while I can't say how
it compares to PySerial, I believe it's fair to say at
this point in time that PySerial is the _de facto_ standard
way to do serial port stuff in Python.  If it doesn't do
what you need, it's probably a good idea to at least point
that out in its mailing list so that it can be improved.


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