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From: wtm@neoucom.UUCP
Newsgroups: rec.autos,rec.autos.tech,comp.misc
Subject: Re: '86 Camaro Computer System
Message-ID: <581@neoucom.UUCP>
Date: Mon, 11-May-87 10:46:16 EDT
Article-I.D.: neoucom.581
Posted: Mon May 11 10:46:16 1987
Date-Received: Wed, 13-May-87 06:37:23 EDT
References: <5701@eddie.MIT.EDU> <594@ur-cvsvax.UUCP>
Organization: Northeastern Ohio Universities College of Medicine
Lines: 57
Keywords: Rom listsings/Serial Data I/O
Xref: utgpu rec.autos:1420 rec.autos.tech:752 comp.misc:472
Summary: GMP-4 made in Kokomo Indiana


I had a job interview about 2 years ago to work for GM as a
contract employee owned by a head hunter agency rather than GM
itself.  At the time, they were producing the GMP-4 microprocessor
for use in their ECM.

The GMP-4 is a semi-custom version of the 6809.  I didn't really
get a chance to see how different it is from a stock 6809.  They
were using an IBM mainframe and cross-assembler to develop the
code.  As the previous poster said, all the code is written in
assembly level.  The unit contains 32K of ROM, which is a lot of
code to write in assembly.  The listing was 4 data binders, each
aobut 10-15 cm. thick.  The code is very thready, and would
probably be very difficult to wade through without the source
(ugh!).  The main loop of the control program is desgined to
execute at least once every mS.

Much of the code is dedicated to the so-called `limp home' modes
that determine default parameters to substute when some of the
engine sensors fail.  There is also some on-board interface
software that allows the ECM to talk to the service shop diagonstic
unit.

GM does very extensive field proving of the ECM.  Once the unit has
been thoroughly tested off road on GM's test track, the four people
on the coding team serve as guinea pigs for the ECMs.  They use
Citations with Motorola diskless development systems in the back
seat.  The development system is wired to a `heads-up display' that
is velcroed to the dashboard.  The display has toggle and rotary
switches that that allow the driver to select from a number of
advance curves, etc that are under consideration.  It was quite
amusing, as I got to drive with a guy in a Citation that could blow
away almost anything else on the road.  The only problem was that
its tires really weren't up to the power capability of the engine.

They were really amazed to have an interviewee that could say
phrases like "top dead center" and "mass air flow sensor", let
alone know what they meant.  I didn't take the job because the
arrangement of working through the headhunter was pretty sleazy.
I've thought about trying to go back and get a job there directly
though GM, as it looked like a pretty neat place to work.

In summary, I don't think it would be a real good idea to try to
hotrod the ECM yourself.  If you did something wrong, you might get
into a situation where you developed uncontrollable acceleration or
some nasy situation (the idle stop on some engines is controlled by
an electric motor).  To me it looks like the design
work behind the ECM is pretty thorough, and you probably couldn't
do too much to tweak the engine for performance.  The ECMs do,
however, have a maximum speed of 85 MPH.  I have a friend that
works for Goodyear that exlained that.  The FBI was outfitting some
Chevy Caprices for high speed tires and came across that fact.
They had to go back to GM to get some cutsom ROMs burned that would
let the cars go faster.  Tney needed to do that so they could catch
people with older analog cars or imports (grin).

  --Bill