Calculating the multiple checksums

[Chris@HPTuners]

Okay, so i've been doing a lot of stuff but understanding the checksum routines is not one of the things i have prioritized. I know where the checksums are and also found a table that stores the segment locs for my particular o/s. i'm sure it's just a simple refernce somewhere to this table and then a cksum alg etc.

Anyone already made any progress?

[Guest]

Could you specify what model year box involved and
OS number and calibration file no: if avail

[Chris@HPTuners]

okay so here's something that i found works for segments 2 to 8 ;D

1. sum all the words from ($segstart+2) to ($segend)
2. AND with $FFFF (to mask the lower 16 bits)
3. Xor with $FFFF
4. ADD $01

checksum is at $segstart. Eg. for seg2 $8000

seems to work for me. Somebody else pls try this if possible.

Also, I am not sure about segment 1 yet. Anyone any ideas?

[Keith@HPTuners]

Thats how its done.. its something I'm incorporaring into PCM Edit soon.

I'm not sure about seg 1 yet either.

[lndshrk]

Instead of doing "XOR w/ FFFF".

Consider doing logical negation ;D

In boolean logic:

A ^ ONES == *A

Or any variable XOR'd with a varable the same # of
bits all high/one is the same as logical negation.

AKA "One's Complement".

The Addition of one makes it the "TWO's Complement"

Ones Complement is the logical inverse.

Twos Complement is the mathematical inverse.

[Keith@HPTuners]

Here is my VB code for anyone interested... note that I have more formatting code in there that I removed for readability.

  'Set our buffer size
  ReDim Buffer(1 To 2)


  'Read until EOF
  Do Until EOF(iHandle)
    Get #iHandle, pos, Buffer
    
    b1 = Buffer(1)
    b2 = Buffer(2)

    If pos > 2 Then checksum = checksum + (b1 * 256) + b2

    pos = pos + 2
  Loop

  checksum = checksum And 65535
  checksum = checksum Xor 65535
  checksum = checksum + 1

[Keith@HPTuners]

To do segment one, you do the entire segment exlcuding the csum at loc 0x500.

I incorporated all of this into PCM_Edit including segment identification.

[Guest]

do you explain this to me that I do not understand it?

Thanks


1. sum all the words from ($segstart+2) to ($segend)
2. AND with $FFFF (to mask the lower 16 bits)
3. Xor with $FFFF
4. ADD $01

checksum is at $segstart. Eg. for seg2 $8000

[The_Highlander]

What happens if you flash with the incorrect checksum?

[Keith@HPTuners]

PCM won't run the OS code after boot.

[danny]

To do segment one, you do the entire segment exlcuding the csum at loc 0x500.

Define entire segment 1 ... 0-> 4FF, then exclude seg2 - 8, then continue until end of file ????

Or, entire file from start to finish excluding csum at 0x500 ?

Dan.