Codeword to ignore checksum

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setzi62

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	Re: Codeword to ignore checksum « Reply #15 on: November 12, 2010, 02:42:25 AM »

Very good , then I might have a look again at this uVision Simulator, of course if I find
some spare time.


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k0mpresd

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	Re: Codeword to ignore checksum « Reply #16 on: December 03, 2010, 01:51:16 PM »

Quote from: setzi62 on November 08, 2010, 10:42:16 AM

Coding the ECU as test model is done in the eeprom, you have to change some data values:
in pages 1 and 2 you will find 69,C1, and A5, replace these by 8E,5A, and D2,
then update the checksums of both pages. I believe you (or other experienced users)
can manage this without more detailed instructions (and the noob's anyway shouldn't
do).

I do not know what could be changed by setting to test model besides the following:
- the data checksum results will be ignored by the ECU,
- you can start a programming session even if the ECU is locked for some time after
sending a wrong security key,
- you can download data to the flash without ciphering and compressing.

On ME7.5 images, when you have started a programming session (85) and
are requesting ecuIdentification with param 9B, the last string you get has 5 characters.
If the last character of this string shows a '*', this indicates your ECU is coded as test model. I think this is not done for ME7.1 images.

Be aware: this results from code reading and simulations, not yet tested by me on real hardware.

wow. this is awesome info and exactly what i was looking for. well, kind of exactly what i was looking for. many many thanks for this!


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prj

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	Re: Codeword to ignore checksum « Reply #17 on: September 20, 2012, 06:12:09 AM »

Thanks from me as well and +rep to setzi62.

I will test this today/tomorrow.


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dream3R

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	Re: Codeword to ignore checksum « Reply #18 on: November 26, 2013, 06:53:52 AM »

Blast from the past but wanted to add that this is implemented in Volvo ME7 ECU's.

Quote

mov [-r0], r8
seg023:E19A mov [-r0], r7
seg023:E19C mov [-r0], r6
seg023:E19E movb rl4, CW_NOROMCHKRESET
seg023:E1A2 cmpb rl4, #55h ; 'U' ; If there is 0x55 here skip checksum checks
seg023:E1A6 jmpa cc_Z, loc_DE3DA
seg023:E1AA movb byte_300F2E, ZEROS
seg023:E1AE mov r4, word_303D76
seg023:E1B2 and r4, #0DFFFh
seg023:E1B6 or r4, #4000h
seg023:E1BA mov word_303D76, r4
seg023:E1BE mov r7, r4
seg023:E1C0 and r7, #1800h
seg023:E1C4 jmpr cc_NZ, loc_DE1DC
seg023:E1C6 movb rl4, byte_303362
seg023:E1CA cmpb rl4, sub_17800+1
seg023:E1CE jmpa cc_NZ, loc_DE3E2
seg023:E1D2 movb rl5, byte_303366
seg023:E1D6 cmpb rl5, #1
seg023:E1D8 jmpa cc_Z, loc_DE3E2


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How to work out values from an A2L

http://nefariousmotorsports.com/forum/index.php?topic=5525.msg52371#msg52371

Starting Rev's http://nefariousmotorsports.com/forum/index.php?topic=5397.msg51169#msg51169

noobs read this before asking http://nefariousmotorsports.com/forum/index.php?topic=9014.0title=

ORGORIGINAL 05 5120 creator for Volvo
ORIGINAL Datalogger (Freeware) Author
ORGINAL finder of the 'extra' torque' limits
I don't have ME7.01 A2L I just use ID

antoffka666

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	Re: Codeword to ignore checksum « Reply #19 on: July 27, 2018, 03:13:04 AM »

Hello, I changed the data in EEPROM (69,C1, and A5, replace these by 8E,5A, and D2) , flashed in ECU , and received a character (*) in the block description . After I flashed the file with the wrong checksum and after two launches ECU stopped switching on .
I repaired my ECU with flash backup eeprom and firmvare but did not understand what this manipulation gives.
I originally did this to get a working LC in 8E0909518F 0003_363670 , but so far nothing has happened.


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prj

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	Re: Codeword to ignore checksum « Reply #20 on: July 27, 2018, 03:29:29 AM »

Look on the forum in ME7.1.1 emulator thread, I described exactly how to turn everything off.
This only disables running checksums not startup sums.


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antoffka666

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	Re: Codeword to ignore checksum « Reply #21 on: July 27, 2018, 04:21:47 AM »

Quote from: prj on July 27, 2018, 03:29:29 AM

Look on the forum in ME7.1.1 emulator thread, I described exactly how to turn everything off.
This only disables running checksums not startup sums.

I understood ! Thank you!


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antoffka666

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	Re: Codeword to ignore checksum « Reply #22 on: July 30, 2018, 11:00:10 PM »

I changed the data in EEPROM (69,C1, and A5, replace these by 8E,5A, and D2) in 4B0906018DJ_366458 and changed variable 0x384FF0 to 386000 . No errors (p0601 checksum error) , 3 days cars work perfect , LC work ! Thank you !


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360trev

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	Re: Codeword to ignore checksum « Reply #23 on: September 23, 2018, 12:30:19 PM »

Quote from: setzi62 on November 08, 2010, 03:52:51 AM

seems like my last post was cut when hitting a german letter ...

In damos/a2l you can see that the codeword CW_NOROMCHKRESET is used only
in the function URROM which is named "EGAS Ueberwachungskonzept: ROM-Test"
(electronic power control supervision concept: ROM-test).

By patching the NOP's and setting the codeword to "55" you could skip the EGAS-checks,
but the data checksums which are calculated/checked when the flash system is running can
not be disabled using the codeword CW_NOROMCHKRESET.

I think the data checksums can be disabled by coding your ECU as test model in the EEPROM.

I know this is an ancient post but i've just been exploring a ROM file which was given to me which works no problem but had non corrected checksums present. After a little analysis by comparing the rom to the original firmware I discovered;

---------------------------------------------
0x000668b8 ( 420024): cc -> ea jmpa cc_Z,jmp +244 CW_NOROMCHKRESET Patch
0x000668b9 ( 420025): 00 -> 20
0x000668ba ( 420026): cc -> ee
0x000668bb ( 420027): 00 -> 6a

CC 00 is the machine code 'NOP' (No Operation, i.e. do nothing) and it was replaced with an
EA 20 which is a conditional jump relative based on the previous instruction which does the CMP against 0x55 in hex... which is normally set to 0'...

0x0001165a ( 71258): 00 -> 55 CW_NOROMCHKRESET

Which surprise surprise they've set to 0x55 which means it always does the skip...

And then further to that they also set to 0x55 another CODEWORD,

0x00011b21 ( 72481): 00 -> 55 CW_NOZYKLROMCHK - disable cyclic rom monitor checksums

I believe this is the one which the OP was interested in all along. I believe this disables the Multipoint Cyclic checksums from being checked by the rom monitor...

And all this was done on a very expensive car without the customer having any idea what they did... WTF! Why didn't they just re-calculate the checksums??!?!?! fine for R&D purposes but there is no way I would do this to anyone's personal car and leave it like that.


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