Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!mcrware!ric
From: ric@mcrware.UUCP (Ric Yeates)
Newsgroups: comp.realtime
Subject: Re: Is polling possible with OS9000 device drivers
Summary: Yes.
Keywords: polling SCF
Message-ID: <4693@mcrware.UUCP>
Date: 18 Jan 91 15:25:20 GMT
References: <1991Jan16.174652.10867@computing-maths.cardiff.ac.uk> <1991Jan17.070502.16206@ncsuvx.ncsu.edu>
Reply-To: ric@mcrware.UUCP (Ric Yeates)
Organization: Microware Systems Corp., Des Moines, Iowa
Lines: 28


Polling people:

Polling is directly supported by OS-9000.  You simply set a couple of
items in the descriptor and POOF!, your driver is a polling driver. 

In OS-9000, polling simply means that if SCF does not already have
enough characters to satisfy a request (from previous calls to the
driver's read routine), it calls the driver's read routine.  If SCF
wants to do some output, it calls your write routine with a buffer of
characters.  Some extra programming may have to be done if you want
type-ahead to work very well though.  (type-ahead == typing characters
when no application is requesting input).  The amount of work is
dependent on the chip and the designer's intentions. 

"Does this system work?" Yes.  The keyboard/monitor driver on the PC is
polling on output, but interrupt driven on input. 

Ric


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Ric Yeates                                             Microware Systems Corp.
  "I found these opinions on the floor, so I don't think they belong
                                                              to Microware."
                         1. Grease Generously
                         2. Wax Philosophically
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