A Newbie Question

[steve ravet]

JTesta1966 at aol.com wrote:

> I'm trying to learn to program some proms, I have a few hex programs, and I
> have a proprietaery program for programming 1986-87 GN proms. Thats neat,
> BUT, I'd like to find a resource on what locations mean, what purpose they
> serve, and what the common adjustments are in those locations. I'm not asking

That's what we're all after...  Look for Programming 101 on the DIY_EFI
WWW page. There's a list of tables and their locations in the PROM
image.  It's for a 1227747 ECM but there are lots of similarities. 
While looking at the 101 project pull up a 747 bin in your hex editor
(from the ftp site), look back and forth, and you'll see how the tables
"look" in binary.  The 3 dimensional tables are easy to see, the others
are harder.

> $33F0   AA  AB AC CD EE FF CC DD-EE FF AB AC AD AE 99 F0   ..(..!.ac........

Easy.  $33f0 is the address where the next 16 bytes are.  $aa is at
$33f0, $ab is at $33f1, and $f0 is at $33ff.  Hex numbers start at zero,
and count to f before starting over at zero. 
1,2,3,4,5,6,7,8,9,a,b,c,d,e,f,10,11,12,13,14,15,16,17,
18,19,1a,1b,1c,1d,1e,1f,20, etc.  Hex 0 to hex $ff covers decimal values
0 to 255.

The dots and stuff on the right are the ascii characters that correspond
to the hex values.  It has no significance, except that if the bin you
are looking at has embedded copyright messages or something like they'll
be obvious on the ascii side.  The hex bytes are the important thing,
just ignore the characters.

> 
> I know the first number is the base memory address, and each of the 15 values
> are a parameter till the next line which would go to $3400, but the last
> pieces of info on that like..the ...(.!..ac...... stuff..what is that? And
> what signifigance does it have? Is it that lines entry for the overall
> checksum? Maybe someone can explain that to me as well...ANYWAY..in the table
> (the spreadsheet) I have, the last entry in a line is like KMRPMHI which I've
> gathered was a GM engineer abbreviation for hi max rpm hi. Anyway...where can
> I find this info in the chip in a hex editor, or what could I open the rom or
> bin file to SEE that info. My intention is to go beyond ONLY doing Buick

That's the hard part....  The only way to locate the tables and other
values (without reading GM docs) is to guesstimate what a value/table is
for, change it, and observe the effect either on car or on the bench. 
If you're an assembly whiz you can disassemble the code and infer what a
lot of the data is.  It's a skill, and something that you get better at
the more bins you stare at.  right Bruce?


-- 
Steve Ravet
steve.ravet at arm.com
Advanced Risc Machines, Inc.
www.arm.com