[Gmecm] disassembly 101 / writing a commented hack

[davesnothereman at netscape.net]

I use Donald Whisnant's (spelling?) code seeking disassembler.  It's 
freeware written to disassemble code from GMECM's.  Tunercat also has 
one, but I'm not as familiar with it.  IDA Pro is also good, but not so 
free.

Is there a data definition file for the norstar ALDL stream?  That 
would at least provide the correct order to the ALDL data words if you 
can find the ALDL xmit table.

Most of the ALDL tables I've looked at begin with the prom id byte 
located in the beginning of the calibration.  If you know or can work 
out the calibration address then you might be able to make a guess at 
the beginning of the ALDL table.

You're famaliar with the reset vectors located at the end of Motorola 
code... use those to separate code from cal. data.

If you're working with a P4 ecm, look for hardware addresses in the 
3XXX range and attempt to use those with known calibrations from other 
P4's to locate specific portions of code.  Use pattern matching to 
attempt to locate and  identify some common routines such as spark 
timing calculation.

There's probably people much better at this than I am who can offer 
better clues.  But will they?

Zaphod

-----Original Message-----
From: William Lucke <william.lucke at highspeedlink.net>
To: gmecm at diy-efi.org
Sent: Sun, 14 May 2006 14:53:22 -0400
Subject: [Gmecm] disassembly 101 / writing a commented hack

   I'd like to get started hacking the OBDI Cadillac Northstar computer 
(). I have a couple of different BCC's, as well as a dyno program that 
only has engine management turned on.

  I'm familiar with assembly and have worked with commercial 68HC11's in 
development boards. I'm familiar with the concepts of disassembly and 
I'm ready to devote the time necessary to reverse engineer this 
program.

 What I'm not sure of, however, is where to start.
 What's the best disassembler to use on GM chip images?

  Is there a listing of the memory locations of the data for the ALDL 
stream? Other than starting at the beginning, I'm not entirely sure how 
to enter the program and know what's what.


 Will
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