Fun with Checksums.
 

Using an editor to do a custom map on a pr3. I am now trying to get the checksum back to its original. Any advice/tips?

I am just starting to read up on it tonight, so im sure ill figure it out, but any help is appreciated.

FYI:
original checksum is: 1e8900
modified checksum is: 1e8d00

TIA,
Dave

Re:Fun with Checksums.
 

You are dealing with the checksum of the whole .bin, which is irrelevant.

The .bin is dealing with an 8 bit checksum... the ECU counts up all the bits of data from 0-255 and then starts back over at 0. Like so:

0, 1, 2, 3, 4, .... 253, 254, 255, 0, 1, 2, 3,... etc.

You have to tweak things so that the whole .bin winds up having an 8 bit checksum of 0. This should help you:

http://www.keil.com/download/files/check8.zip

Unzip check8.exe to the dir you have your .bin located at, go to that directory from a DOS/Command prompt, and you will enter something like I have below:

C:\Leeds directory of gay porn and honda bin files> check8 pr3.bin

Check8 will now tell you how far off your checksum the .bin is. There is supposed to be some way of getting check8 to modify your checksum if you know of a blank memory address it can modify, but it doesn't work so don't waste your time. Just find a blank spot with the hex editor and modify one of the stretches of FF's until everything is groovy.

Re:Fun with Checksums.
 

Porn directory, howd you know :P
Thanks for the info man, appreciate it.

Re:Fun with Checksums.
 

In addition, make sure the hexidecimal number you get is subtracted by FF, then add 0x01 to your result. Plus, make sure the "empty address" is before address 0x4FFF, which is address space that the ECU checks.

Re:Fun with Checksums.
 

:o Holy Crap you guys!!! How the hell do you get to know all this stuff?

Re:Fun with Checksums.
 

it all comes down to eating the tender most tasty salmon my friend.

Re:Fun with Checksums.
 

---- salmon, old women eat that ----. Raw tuna is where it's at, with extra wasabi. >:)

Re:Fun with Checksums.
 

I was always taught to stay away from tuna http://index.driftkids.com/throwupen.gif

--edit--
Now he makes me steal the 6K image.. sheesh.. cry babies. :-[

Re:Fun with Checksums.
 

^ lol... someone getting pissed about bandwidth