Checksum Calculation

adrian · Post by **adrian** » Wed Mar 19, 2003 2:03 am

Some GM codes ($11 for example) have the checksum in an odd location. The area the checksum is calculated on is from 5000 to FFFF but excluding 6000 to 6007, with the checksum located at 6006 & 6007.
Is there any way of incorporating this into your program

Post by **supportf** » Wed Mar 19, 2003 1:46 pm

Hmmm, I can look into this, yes. It might be difficult to create an interface that will allow you to insert an unlimited number of exclusions. but I might come up with something.

maybe an "add exclusion" dialog box or something ...

I'm working hard on GMECM Edit v2.0, and I'll look into this for that version.

Thanks Adrian!

adrian · Post by **adrian** » Mon Sep 12, 2005 3:51 am

I Know this suggestion is old but I now have a furthur suggestion related to checksums.
Some of the '90s GM codes(AU) use multiple checksums (I've seen up to 3) with the final saved checksum being the sum of these checksums.
Is this a possibility??

Seeing I'm the only one asking for these weird things I understand if it's at the bottom of the list

Chuck B · Post by **Chuck B** » Wed Nov 09, 2005 4:37 pm

I have been using the RT on some VW bins.Some of the later ECUs have hugly complicated multiple checksums.I would be tickled to death to see this feature so I don't have to use a hex editor.

Post by **Mangus** » Sat Nov 12, 2005 12:41 am

You can add multiple checksums in tunerpro. If you need different calculations, you'd need to provide details on the VW checksum calculations.

Chuck B · Post by **Chuck B** » Wed Nov 16, 2005 4:47 am

There is about 15 different sections that are added togher and checksumed.Then a constant is subtracted from the checksum to form another checksom in another location.

The new stuff has a really crazy checksum routine where there are many checksums like this and then there are XOR checksums as well(no i still havent figured out these cars).

Post by **Mangus** » Wed Nov 16, 2005 7:09 am

Give me specifics (examples) and I'll do what I can.

jma · Post by **jma** » Thu May 25, 2006 10:00 am

I'm working on a weber marelli iaw ecu and I have exactly the same problem. I need to define 3 memory sections and the checksum is the sum of these sections. Moreover a constant to addition at final !

27c256 chip 8000-FFFF

800E checksum store address (2 bytes)

8010-B5FF first section
B800-DFFF second section
E000-FFFF third section

All bytes are accumulated in a 16 bits address and the value 0DF0 is added in the end.

So the- features I need are :
-define several address ranges instead of only one (easier than managing exclusions I think)
-add or substract a constant before storing the checksum

I can send you bin and xdf files.

regards,
Jerome

Post by **Mangus** » Thu May 25, 2006 12:33 pm

Thanks for the info. I'll put some thought into a solution for this.

So, you add each section independently, then add the results and add a constant, like so:

Checksum = SUM(section 1) + SUM(section 2) + SUM(section 3) + <constant>

Is that right?

jma · Post by **jma** » Thu May 25, 2006 2:10 pm

checksum = SUM(section1 bytes, section 2 bytes, section 3 bytes) + constant
is closer to the truth.

Thanks.

Post by **Mangus** » Thu May 25, 2006 2:12 pm

We said the same thing by the associative property of addition.

A + B + C = (A + B) + C = A + (B + C) = etc...

jma · Post by **jma** » Fri May 26, 2006 2:32 am

yes you are right, I just describe how the ecu program is working.

Another idea would be to create a checksum plugin interface for Tunerpro.

Chuck B · Post by **Chuck B** » Wed Jun 07, 2006 5:19 pm

Here is the crazy VW audi checksum circus.

http://www.andywhittaker.com/Audi/ecu/index.html

jma · Post by **jma** » Sun Sep 17, 2006 1:33 am

I was able to use Tunepro to calculate my checksum using an unused area as temporary buffer. It's dirty but it works

I think the easiest way to improve Tunerpro on this point would be to add an "accumulate" option for each defined checksum. This way we could use the checksum storage address as an accumulator not just at as a store address. Should be quite straightforward to implement (just a new checkbox in the interface)

my example :

Sum 8010-B5FF and store @ 800E
Sum B800-DFFF and accumulate @ 800E
Sum E000-FFFF and accumulate @ 800E
Sum 94FE-94FF and accumulate @ 800E (94FE is the address where the final constant 0DF0 is stored)