CRC's..Checksums.. Reverse Engineering!

[antus]

The checksums are the first 2 bytes of the segments. the segment maps are in the index. The index is static.

[Tazzi]

The checksums are the first 2 bytes of the segments. the segment maps are in the index. The index is static.

Man where have I been.. Thats only just all clicked!

Alright... time to put that into the app now.

[antus]

Hehe, heres what I implemented tonight. Back to figuring out the checksum calculations next.

[Tazzi]

Good thinking, Ill do something like that as well.

[charlay86]

This looks fun, too bad I have to renovate the bathroom and kitchen after I finish uni exams this week

[Tazzi]

This looks fun, too bad I have to renovate the bathroom and kitchen after I finish uni exams this week

Uni exams.. bloody waste of time they are.. they make students cram an entire semesters work into a single week, it doesnt stay with them for life, it just proves they can memorize stuff! In Engineering, we were expected to pretty much rope learn 2000+ lecture slides as we could be tested on any one slide, and thats for just the single unit!.

[Tazzi]

Hehe, heres what I implemented tonight. Back to figuring out the checksum calculations next.

Just put something similar together.. looking much better now

The backwards iteration crashed at some point last night.. *sigh*, I dont know at what point it crashed so Ill be starting around the 1/3 mark again.

I think I should do the same as you Ant and focus on the smallest section possible, will cut down processing time by a tonne.

[yoda69]

Uni exams.. bloody waste of time they are.. they make students cram an entire semesters work into a single week, it doesnt stay with them for life, it just proves they can memorize stuff! In Engineering, we were expected to pretty much rope learn 2000+ lecture slides as we could be tested on any one slide, and thats for just the single unit!.

Been there, done that, remember the time doing it well but not the content.
Worst was 1st year Chemical Engineering, having to remember all these chemical equations, where the electrons went, which bits were positively charged and God knows what else as it was too long ago now, definitely put me off doing Chem Eng as a discipline.

[antus]

Ok. The CVN is a CRC16, and the sum is a 16 bit 2s compliment. When calculating the data you need to update the CVN first, as it IS included in the sum. The CVN is not a derivative of the sum (or directly vice versa).

Makes sense really as the scan tools (or PCs) can verify the CVN after reading the bin for warranty test purposes (that's why its in there), but the PCM only needs to do the sum which is quicker in an embedded system like a pcm. CRC can be accellerated with a lookup table, but they are probably looking at it from a space savings angle in the pcm, and its not really needed anyway.

Next steps, figure out how to ID each segment type, handle disabled sums and segments, handle differing numbers of segments, and add partnumber/ID strings.

Also, put this login in to a TP checksum plugin. Probably merge the delco checksum plugin, ls1 checksum plugin, and e38 checksumtool in to one TP5 checksum plugin.

Whos keen to help work on XDFs?

[VX L67 Getrag]

I can always do xdf's but need some sort of reference & then also a previously defined xdf of similar code to get started!