Path: utzoo!attcan!uunet!husc6!mailrus!ames!elroy!jpl-devvax!jplpro!leem
From: leem@jplpro.JPL.NASA.GOV (Lee Mellinger)
Newsgroups: sci.space.shuttle
Subject: Re: Shuttle computer reprogramming
Message-ID: <2993@jpl-devvax.JPL.NASA.GOV>
Date: 5 Oct 88 19:42:04 GMT
References: <6689@nsc.nsc.com> <6980@ihlpl.ATT.COM> <1938@kalliope.rice.edu>
Sender: news@jpl-devvax.JPL.NASA.GOV
Reply-To: leem@jplpro.JPL.NASA.GOV (Lee Mellinger)
Organization: Jet Propulsion Laboratory, Pasadena CA.
Lines: 76

In article <1938@kalliope.rice.edu> phil@Rice.edu (William LeFebvre) writes:
|In article <6980@ihlpl.ATT.COM> knudsen@ihlpl.ATT.COM (Knudsen) writes:
|>Well, the network (ABC) said it was memory limitations.
|>...
|>I gather the programs are compiled with
|>a #define WIND_SPEED 12345 or some such thing
|
|It's not just memory and it's not as simple as changing a constant...
|more on that later.
|
|>One of the flight crew said that every time they want to
|>put a new capability into the computers (like yet another
|>emergency abort scenario), something else has to be
|>taken out.
|
|This is true.  The software used on ascent almost completely fills the
|memory capacity of the computers.  To add anything requires removing
|something else (or at least getting the memory from somewhere).
|
|>So I'll bet every byte of that code is hand-optimized
|>to hell and back.  I doubt any hi-level language,
|>or even C, got anywhere near those computers.
|
|They call the language HAL/S (for "High-level Assembly Language").  I have
                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

HAL/S was written by Intermetrics, a company associated with MIT, and
was named for the then head of the development Dr. Halcomb.  It is a
high level realtime language based on PL/1.  It produces highly
optimized code that in a series of trials against assembly code
written by very senior IBM programmers imposed about a 10% penalty in
time and memory.

|seen some of the flight software (about a page or so) and it looked a
|whole lot like IBM assembly language.  When I saw "BAL" I knew instantly
|what it meant.
|
|>Would someone who knows like to tell us how much RAM & ROM
|>these babies have?  I know they use core memory...
|
|No RAM, no ROM.  They use iron-ferrite core memory.  I believe I mentioned
|in this list previously what I *thought* was a correct figure for the
|amount of memory.  It turns out I was wrong.  It is most definitely 208K
|half-words (IBM-ese for "16 bit word").  That would be 416K bytes.  But
|the machine is only half-word addressable, so giving the size in terms of
|bytes is a little misleading.  Remember that K=1024, so that's almost 213
|thousand half-words (it's possible that some non-technical types would
|incorrectly say 212K or 213K).
|
|
|			William LeFebvre
|			Department of Computer Science
|			Rice University
|			<phil@Rice.edu>

The computers are 4Pi/AP-101's which are esentially ruggedized IBM
360's in a small box.  That is the four prime computers, the fifth is
a Rockwell/Autonetics machine.  All four are online during launch and
landing on a synchronized bus.  They all vote on the solutions, and if
one dissagrees, the others vote it out and it is taken offline.  The
Autonetics machine is there in case there is a generic HW or SW
failure that would take out all four prime machines.

To answer someone's suggestion, they cannot be downloaded from the
ground.

Lee


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|Lee F. Mellinger                         Jet Propulsion Laboratory - NASA|
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