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What do I need to do know about Hex Editing PSX save files?

R

Renegade

Wearer of Army Boots
I have a little prior knowledge about hex editing PC game files.

but when I look into PSX save game files (e.g. .mcr) the hex gets translated into nothing but bullshit. I am using Hex Workshop...

not even a sensible thing can be seen (unlike for PC ones).

exactly what do I need to know? no bs, please...
 
M

Mirco Muck

New member
All I can say is that ePSXe compresses its savestates, so editing is somewhat impossible except you know the exact algorithm for de/encoding.

Memory Card Savestates instead are mostly uncompressed and editable, but some games calculate a checksum on thier data, so editing is also somewhat tricky.

But you should try to search for game specific values (e.g. money, hp) using Motorola Byte ordering
 
Last edited:
Cyberman

Cyberman

Moderator
Moderator
Renegade said:
I have a little prior knowledge about hex editing PC game files.

but when I look into PSX save game files (e.g. .mcr) the hex gets translated into nothing but bullshit. I am using Hex Workshop...

not even a sensible thing can be seen (unlike for PC ones).

exactly what do I need to know? no bs, please...
Click to expand...

Umm restrain yourself from ephithets there :)

I can give you lots of BS.. but this is in the wrong forum this is more gaming related. However since I am working on game save state plugins (what I finally am making a plugin that is going to be public?!).

Heres the deal. DON'T try editing the SAVE file as there are several game save editors out there. SOME GAMES HAVE CRC32 checks to be sure you haven't EDITED the game save as well. Final Fantasy 8 and 9 are a few of such games.

Anyhow here is a link to a currently under development PSX game card editor called PSXMem Tool. I recomend using that instead, it will save you a lot of insanity. The memory cards have a specific format a directory and a ICON for each saved file. What this means is that unless you dig up this information on the net.. you won't be able to do much. I have the information, but since you want to edit games and not play around with the format of the stupid card, just use PSXMem Tool instead.

My FF8 Game save plugin might be in the next PSXMem Tool though I doubt it.. the author hasn't replied to me about his progress with testing it :) So .. can't do anything more with it tell he tells me the plugin works with his compilor and DLL library loading system.

Cyb:linux:
 
euphoria

euphoria

Emutalk Member
I'm making a savestate editor for Chrono Cross and i'm a bit lost in the CRC section. Is there a certain way of calculating it or is there 2^32 ways to do it or at least does Squaresoft do it same way in all their games? If anyone has knowledge of this i'd apreciate the help.
Besides i haven't found all the necessary values from the file so the CRC isn't needed at the moment.

PS. I use UltraEdit to look at the .mcr's and it looks ok. Keep in mind if coding a savestate editor that some values are in 7-bit, 9-bit, Xbit to save space. So you can't search changed values byte by byte.
 
OP
R

Renegade

Wearer of Army Boots
i've heard of motorola and intel byte ordering.

<lightknight>does it haf anyting to do wit programing a 1337 gc emulatore??3?3?3?3</lightknight>

seriously though, what is it? is it some sort of thing which rearranges data so that it becomes unreadable to the human in a hex editor?
 
Cyberman

Cyberman

Moderator
Moderator
Renegade said:
i've heard of motorola and intel byte ordering.

<lightknight>does it haf anyting to do wit programing a <a href="glossary.php?&ltr=#">1337</a> gc emulatore??3?3?3?3</lightknight>

seriously though, what is it? is it some sort of thing which rearranges data so that it becomes unreadable to the human in a hex editor?
Click to expand...

Ummm Motorola = Big Endian Intel = Little endian.
It's the ordering of the bytes in words longs and long longs
For example
Big Endian:
WORD MSB LSB
LONG MMSB MLSB LMSB LLSB
Little Endian:
WORD LSB MSB
LONG LLSB LMSB MLSB MMSB

It's handy for however the data was stored in the Game Save you are dealing with IE money likely would be stored in a LONG but what byte ordering is a good question.

Originally posted by euphoria
I'm making a savestate editor for Chrono Cross and i'm a bit lost in the CRC section. Is there a certain way of calculating it or is there 2^32 ways to do it or at least does Squaresoft do it same way in all their games? If anyone has knowledge of this i'd apreciate the help.
Besides i haven't found all the necessary values from the file so the CRC isn't needed at the moment.
Click to expand...
It depends on the polynomial they used, as for the same way.. doesn't seem that way, they seem to change the polynomial for each game.

FF8 uses a 16bit CRC with a polynomial of 0x1350 or
X^12 + X^9 + X^8 + X^6 + X^4. FF9 used a 32 bit CRC.

The best way to 'break' it is to take a known save state for example At the VERY beginning of Chrono Cross. guess what data is what inside the file then apply polynomials to the data tell you get a match. You have about 2^16 with a 16bit CRC and 2^32 tries with a 32bit CRC.

Might take an hour or two or over night to do but You'll know for sure. The other problem is what is the CRC calculated on. you have to know what the save state data area the PSX is doing the CRC check on. It would be cool if you could extract the CRC tables from the game itself .. that's the best way to know the CRC calculation to be honest.

Cyb
 
OP
R

Renegade

Wearer of Army Boots
ah. it looks like i need supreme knowledge of assembly lang to understand this crap :(
 
Cyberman

Cyberman

Moderator
Moderator
Renegade said:
ah. it looks like i need supreme knowledge of assembly lang to understand this crap :(
Click to expand...
Ummm what has that to do with generating CRC'S?
not really anything.. you don't need to know Assembly language for say the X86 series to Calculate a CRC you only need to know the CRC polynomial and the initial state.

For FF8 it's relatively simple fortunately. Start State is 0xFFFF and it's a 16bit CRC the polynomial is 0x1021 might be the same they used for Chrono Cross and FF9 even.. GOK FF9 was not nearly as popular as FF7 and FF8 so ... I doubt anyone wanted to hack the saves :)

The size of the save data is 0x1350 or 4944 bytes for FF8.
CRC's are tricky buggers that's all. here is the code I use for doing the CRC calculation in FF8
Code: 
   while ( Length > 0)
   {
      Index = (checksum >> 8) ^ *dataptr;
      Val = (checksum & 0xFF) << 8;
      checksum = CS_TBL[Index];
      checksum ^= Val;
      dataptr++;
      Length--;
   }
   checksum = ~checksum;
Do you see assembly language instructions in that?

Cyb
 
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