reverse engineering formulas from xsmonitor_frame about mercedes-hacking-docs HOT 5 OPEN

have partially found formula.
there is two bytes 02 01 followed by 3x binary32

53 53 45 4e 5f 42 00 08  02 01 00+00+00+00 00+00+ |SSEN_B..........|
00+3f 00+00+20+c2 02 b0  43 13 41 75 df 65 6e 6c  |.?.. ...C.Au.enl|

still don't know what the first one is but the others are multiplier + addend

00+00+00+00
00+00+00+3f                       # multiplier (0.5) Float Little Endian (DCBA)
00+00+20+c2                       # addend     (-40) Float Little Endian (DCBA)

# msg header
05 80                             # Identifier for next can frame
02 00
08                                # str len
SAM_V_A2                          # string (ECU NAME)
00 17                             # id
00 00 00 00 00
04                                # msg count (4)
00

# msg position
07 80                             # Identifier for next msg pos frame
00 01 00                          # pos number (1/4)
0A                                # str len
T_AUSSEN_B                        # string (MSG NAME)
00                                # offset
08                                # length
02 01
00 00 00 00
00 00 00 3F                       # multiplier (0.5) Float Little Endian (DCBA)
00 00 20 C2                       # addend     (-40) Float Little Endian (DCBA)
02                                # str len
°C                                # string (unit)
13                                # str len
Außenlufttemperatur               # string (description)

from mercedes-hacking-docs.

the UNIT calculation can be hard to workout, and is not present in the XSMonitor files. For instance, T_OEL in gearbox (722.6) can be calculated as

T_OEL - 50

Where as the same signal but from the engine is

T_OEL - 40

So In general, I guess the formula and just see what makes most sense based on actual values in DAS.

from mercedes-hacking-docs.

Hm.. I can find the same bytes on other signals where the same formula applies. Maybe we can create some formula database, at least?

from mercedes-hacking-docs.

This is super cool! I never glanced at those bytes before! Thank you so much! I will get to work on a v4 parser with this knowledge.

Now assuming you have XSMonitor, there is a CSV file in there which contains a huge CAN matrix showing which ECUs send which can frames, and which ECUs read those can frames, as well as transmit intervals. This has been a huge pain for me as I can't seem to find any reference to this kind of information in the .dat files.

Any ideas? 😁

from mercedes-hacking-docs.

No clue, I am completely beginner started learning about CAN two months ago, don't have any of that tools. Let's see what bytes left

edit: today started learning python but it is really hard to me (used to write shell scripts)

have modified your parse_dat_v3.py to create C structs but it doesn't work with enum. I fill the structs with memcpy() so these structs are packed bitfields. guess have to add enum as comments-only information.

What I don't know is how to print formulas (comments-only too?) if you don't mind send me commit on gitlab you are author of that script and the only one who can fix

from mercedes-hacking-docs.