rec.autos.simulators

N4 Setup file format

Bart Westr

N4 Setup file format

by Bart Westr » Fri, 27 Jul 2001 16:55:06

Perhaps it is a CRC16 (cyclic redundancy check) with the result only in
butes 24-25. CRC is a combination of adding and shifting based on polynomial
math. I forgot how it goes exactly, but I can remember that it is much
stronger than simply XOR ing the data, which can let two-bit changes
undetected.

The CCITT 16bit algorithm (X^16 + X^12 + X^5 + 1). Examples: (from google
search).
http://www.racesimcentral.net/
http://www.racesimcentral.net/
http://www.racesimcentral.net/

Bart Westra


> Over the past few days I've been looking into the N4 car setup files with
a
> view to making a setup utility similar to GRE for GPL.

> I've found allot of the values and have made a small VB program that can
> extract/edit the values individually, but I have hit a big brick wall.
Papy
> seem to have added in a checksum at bytes 24-27 and if the value stored in
> those bytes doesn't correspond to the rest of the file it won't work in
N4.
> The problem is I just can't find any relationships between the checksum
and
> the rest of the file, here's an example:

> I make 9 identical (but for increasing one of the damper values by 1 each
> time) setups in N4

> damper val        bytes 24-27            value at 24-27
> at byte 568 (int)                               (float)
> 01                      BE C5 2A 4C        44766970
> 02                      B6 B3 2A 4C        44748500
> 03                      51 05 2A 4C         44569920
> 04                      B9 C4 2A 4C        44765920
> 05                      41 E9 2A 4C         44803330
> 06                      49 9F 2A 4C         44727590
> 07                      B1 B2 2A 4C        44747460
> 08                      88 14 2A 4C         44585500
> 09                      70 39 2A 4C         44623300

> Can anyone make any sense of it cause I can't? The only value that has
been
> changed is at byte 560 so I can't see how the values at 24-27 relate to
the
> data in the rest of the file, I'm completely stumped on this if anyone
could
> offer me any help it would be greatly appreciated.

> Thanks,


GBB

N4 Setup file format

by GBB » Fri, 27 Jul 2001 23:57:19

Well it's not CRC16 because the last 2 bytes do change with more setup
changes but it might be CRC32.

Thanks for the idea,
Alex


> Perhaps it is a CRC16 (cyclic redundancy check) with the result only in
> butes 24-25. CRC is a combination of adding and shifting based on
polynomial
> math. I forgot how it goes exactly, but I can remember that it is much
> stronger than simply XOR ing the data, which can let two-bit changes
> undetected.

> The CCITT 16bit algorithm (X^16 + X^12 + X^5 + 1). Examples: (from google
> search).
> http://www.sxlist.com/techref/8051/crc16.htm
> http://www.ptb.de/english/org/1/11/114/infos/crc16.htm
> http://homepage.ntlworld.com/matthew.rowe/micros/virbook/crc16.htm

> Bart Westra



> > Over the past few days I've been looking into the N4 car setup files
with
> a
> > view to making a setup utility similar to GRE for GPL.

> > I've found allot of the values and have made a small VB program that can
> > extract/edit the values individually, but I have hit a big brick wall.
> Papy
> > seem to have added in a checksum at bytes 24-27 and if the value stored
in
> > those bytes doesn't correspond to the rest of the file it won't work in
> N4.
> > The problem is I just can't find any relationships between the checksum
> and
> > the rest of the file, here's an example:

> > I make 9 identical (but for increasing one of the damper values by 1
each
> > time) setups in N4

> > damper val        bytes 24-27            value at 24-27
> > at byte 568 (int)                               (float)
> > 01                      BE C5 2A 4C        44766970
> > 02                      B6 B3 2A 4C        44748500
> > 03                      51 05 2A 4C         44569920
> > 04                      B9 C4 2A 4C        44765920
> > 05                      41 E9 2A 4C         44803330
> > 06                      49 9F 2A 4C         44727590
> > 07                      B1 B2 2A 4C        44747460
> > 08                      88 14 2A 4C         44585500
> > 09                      70 39 2A 4C         44623300

> > Can anyone make any sense of it cause I can't? The only value that has
> been
> > changed is at byte 560 so I can't see how the values at 24-27 relate to
> the
> > data in the rest of the file, I'm completely stumped on this if anyone
> could
> > offer me any help it would be greatly appreciated.

> > Thanks,

reply)

randyri..

N4 Setup file format

by randyri.. » Sat, 28 Jul 2001 03:54:20

Alex,

I have some homemade tools for trying to figure out checksums from
past projects lying around. Send me a few files and describe what
you've figured out already and I'll have a go at it.

Randy

GBB

N4 Setup file format

by GBB » Sat, 28 Jul 2001 04:40:26

Actually forget that, it is a 16bit checksum at 24-25, 26-27 are the start
of the filename....doh

Alex


> Well it's not CRC16 because the last 2 bytes do change with more setup
> changes but it might be CRC32.

> Thanks for the idea,
> Alex



> > Perhaps it is a CRC16 (cyclic redundancy check) with the result only in
> > butes 24-25. CRC is a combination of adding and shifting based on
> polynomial
> > math. I forgot how it goes exactly, but I can remember that it is much
> > stronger than simply XOR ing the data, which can let two-bit changes
> > undetected.

> > The CCITT 16bit algorithm (X^16 + X^12 + X^5 + 1). Examples: (from
google
> > search).
> > http://www.sxlist.com/techref/8051/crc16.htm
> > http://www.ptb.de/english/org/1/11/114/infos/crc16.htm
> > http://homepage.ntlworld.com/matthew.rowe/micros/virbook/crc16.htm

> > Bart Westra



> > > Over the past few days I've been looking into the N4 car setup files
> with
> > a
> > > view to making a setup utility similar to GRE for GPL.

> > > I've found allot of the values and have made a small VB program that
can
> > > extract/edit the values individually, but I have hit a big brick wall.
> > Papy
> > > seem to have added in a checksum at bytes 24-27 and if the value
stored
> in
> > > those bytes doesn't correspond to the rest of the file it won't work
in
> > N4.
> > > The problem is I just can't find any relationships between the
checksum
> > and
> > > the rest of the file, here's an example:

> > > I make 9 identical (but for increasing one of the damper values by 1
> each
> > > time) setups in N4

> > > damper val        bytes 24-27            value at 24-27
> > > at byte 568 (int)                               (float)
> > > 01                      BE C5 2A 4C        44766970
> > > 02                      B6 B3 2A 4C        44748500
> > > 03                      51 05 2A 4C         44569920
> > > 04                      B9 C4 2A 4C        44765920
> > > 05                      41 E9 2A 4C         44803330
> > > 06                      49 9F 2A 4C         44727590
> > > 07                      B1 B2 2A 4C        44747460
> > > 08                      88 14 2A 4C         44585500
> > > 09                      70 39 2A 4C         44623300

> > > Can anyone make any sense of it cause I can't? The only value that has
> > been
> > > changed is at byte 560 so I can't see how the values at 24-27 relate
to
> > the
> > > data in the rest of the file, I'm completely stumped on this if anyone
> > could
> > > offer me any help it would be greatly appreciated.

> > > Thanks,

> reply)


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