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From: jensen@convex.UUCP
Newsgroups: comp.arch
Subject: Re: real-time and apollo
Message-ID: <63900008@convex>
Date: Sat, 12-Sep-87 02:41:00 EDT
Article-I.D.: convex.63900008
Posted: Sat Sep 12 02:41:00 1987
Date-Received: Sat, 19-Sep-87 11:44:12 EDT
References: <249@mv04.ecf.toronto.edu>
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Nf-ID: #R:mv04.ecf.toronto.edu:-24900:convex:63900008:000:1825
Nf-From: convex.UUCP!jensen    Sep 12 01:41:00 1987


The desire to do real time processing on an Apollo is interesting.
As a former employee of the company, I a bit familiar with the
architectural problems on the earlier product lines (DN 6xx, DN5xx,
DN4xx & DSP80).

First, Apollo has not written the interrupt handling code with
"real-time" responsiveness in mind.  The kernel of the operating
system is monolithic, so you have to use the user device driver
facility to access special devices.  There is some overhead associated
with this, which may preclude the responsiveness that you desire.
Although Apollo does have an assembler, it used to be hard to get
ahold of (unless Apollo has changed their distribution scheme).
Lastly, you have no control over anything like interrupt priorities,
thus, getting deterministic response to external events is going
to be hard.

As far as alternative O/S for Apollo systems, I am not aware of
any.  Apollo does not release for general consumption the specific
internal details of their boxes.  Thus you do not know how
memory addresses are allocated, how the memory mangement unit works,
how the display subsystem works, etc.  This is the major stumbling
block to bringing up a non-Aegis O/S.  It can be done, all of the
hardware peices are there to run something like Unix, but with
no documentation, it is near impossible.

Let me make a suggestion.  Since the 3000 (and, presumably, the 4000)
has an AT compatible bus, look into using one of the commercial
"turbo cards" that fit in that bus.  The turbo card can run a
fast "real time" monitor and the Apollo CPU only has to care about
communicating with the other processor.  You may have to hack some
signals on the card, but then again, you may not.  It may be worth
a look.

Good luck with what you want to do.

Bill Jensen
Convex Computer Corp.
{uiucdcs,ihnp4}!convex!jensen