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#926 Otto1980 OFFLINE  

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Posted Thu Apr 9, 2015 2:01 AM

isnt that the rom header of a 4 MB rom?

so by replacing this it with another header works?

 

so BSG and/or BS are the only roms that dont work on skunkboards?



#927 Otto1980 OFFLINE  

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Posted Thu Apr 9, 2015 2:05 AM

isnt that the rom header of a 4 MB rom?

so by replacing this it with another header works?

 

BSG and/or BS are the only roms that dont work on skunkboards?

 

if modifying a part of the rom (e.g. a graphicdata .. some pixels or so) then recreate the header with jagcrypt and it could work?



#928 CyranoJ ONLINE  

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Posted Thu Apr 9, 2015 3:35 AM

isnt that the rom header of a 4 MB rom?

so by replacing this it with another header works?

 

BSG and/or BS are the only roms that dont work on skunkboards?

 

if modifying a part of the rom (e.g. a graphicdata .. some pixels or so) then recreate the header with jagcrypt and it could work?

 

I'm not going to help you copy this game. Go find a debugger and work it out.



#929 ggn OFFLINE  

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Posted Thu Apr 9, 2015 3:45 AM

PIRACY DETECTED!

crane10.gif

PIRACY DETECTED!

#930 Otto1980 OFFLINE  

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Posted Thu Apr 9, 2015 5:24 AM

ggn must be the head of the multimillion BSG business cartel :grin:



#931 rayik OFFLINE  

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Posted Thu Apr 9, 2015 7:02 AM

 

The black list is not the reason why BSG is not working on the Skunk :P

 

Interesting, while no deliberate blacklist, the way the bios was coded effectively locks it out.

 

If I understand some old AA posts correctly, skunkboard bios uses the rom verification space (first $1FFF).  When a rom is loaded, the fist $1FFF is ignored and onnly from $802000 is loaded.  The skunkboard always uses a rom run address as $802000.  Thus any game with a different run address fails to start.

 

This must have been a design decision as the bios does does not use the full 2KB.  Design that was not adopted could have been to create a variable run address, read the run address from the rom header, set that variable with that run address , and then use that variable value as the start for the loaded rom. (I am not a coder so I apologize if the terminology is incorrect)


Edited by rayik, Thu Apr 9, 2015 7:04 AM.


#932 ggn OFFLINE  

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Posted Thu Apr 9, 2015 8:31 AM

ggn must be the head of the multimillion BSG business cartel :grin:

 

My hovercraft is full of eels!



#933 rayik OFFLINE  

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Posted Thu Apr 9, 2015 10:49 AM

[deleted]


Edited by rayik, Thu Apr 9, 2015 11:05 AM.


#934 rdemming OFFLINE  

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Posted Thu Apr 9, 2015 3:00 PM

isnt that the rom header of a 4 MB rom?
so by replacing this it with another header works?

 
Because of technical reasons, the SkunkBoard does not use the header of a ROM file. Thus replacing/modifying the header has no effect if flashed in the Skunk.
 
 

BSG and/or BS are the only roms that dont work on skunkboards?

 
They are not the only ones. The NTSC only version (v1) of Raiden does not work either because of differences in the graphics setup of the Jaguar BIOS and the Skunk BIOS while NTSC Raiden is assuming a certain initial state. The PAL/NTSC version (v2) of Raiden does setup the graphics chip correctly and works on the Skunk.
 
 
 

if modifying a part of the rom (e.g. a graphicdata .. some pixels or so) then recreate the header with jagcrypt and it could work?

 
Recreating the header is not needed. Because the SkunkBoard does not use the header of a ROM file, there is no encryption check thus the ROM does not need to have a valid encryption header. So you can modify part of the ROM before flashing and still have it boot.
 
 

 
Interesting, while no deliberate blacklist, the way the bios was coded effectively locks it out.
 
If I understand some old AA posts correctly, skunkboard bios uses the rom verification space (first $1FFF).  When a rom is loaded, the fist $1FFF is ignored and onnly from $802000 is loaded.  The skunkboard always uses a rom run address as $802000.  Thus any game with a different run address fails to start.
 
This must have been a design decision as the bios does does not use the full 2KB.  Design that was not adopted could have been to create a variable run address, read the run address from the rom header, set that variable with that run address , and then use that variable value as the start for the loaded rom. (I am not a coder so I apologize if the terminology is incorrect)

 
Yes, because of technical reasons the SkunkBoard does not use the ROM header and thus can't use the start-address in the ROM header. Therefore it assumes the start address is always $802000 (like nearly all ROMs). Thus any ROM with a different start address won't work on the Skunk.
 
Not using the start address is IMHO not on purpose but follows from the design decisions of the Skunk. As you say the Skunk uses the space $800000-$801FFFF (8K) for its BIOS and therefore can't store the ROM header of the ROM file it flashes. If you also wanted to store the ROM header on the Skunk so it could use the start address stored in the header, then the Skunk would have needed an extra ROM chip for the BIOS which would have made the design more complex and expensive.
 
You say the Skunk BIOS does not use all the available space in the header thus it could have stored the start address of the flashed ROM at a free spot (variable) in the Skunk BIOS area. This sounds easy but due to how flash memory is written this is not so easy.
Flash memory is not random write access like RAM. To write some value in a flash memory area you need to erase it first. But you can't erase single bytes but only whole pages. The flash chip used in the Skunk has 8 pages of 4KB and the rest of the memory are pages of 32 KB. Thus the Skunk BIOS occupies the first two pages and both pages are used. Thus if you want to store the ROM start address you need to copy the contents of a flash page (in this case the page where the Skunk BIOS resides) to RAM, erase the flash page and then reprogram the flash page with the ROM start address "variable" filled in. This is doable but this increases the risk that due to errors/power failures the Skunk BIOS gets corrupted and won't start anymore (thus bricking the Skunk). The pages containing the Skunk BIOS are also write protected to prevent accidental erasure of the Skunk BIOS. Also by changing data in the Skunk BIOS area, the encryption header possibly becomes invalid and the Skunk BIOS won't boot anymore.
And if you are able to store the ROM start address this way, this does not solve the problem of ROMs that depend on the ROM header in other ways besides the different start address.
 
Robert



#935 CyranoJ ONLINE  

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Posted Thu Apr 9, 2015 3:29 PM

Yes, because of technical reasons the SkunkBoard does not use the ROM header and thus can't use the start-address in the ROM header. Therefore it assumes the start address is always $802000 (like nearly all ROMs). Thus any ROM with a different start address won't work on the Skunk.

 

 

JCP -B ....



#936 82-T/A OFFLINE  

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Posted Thu Apr 9, 2015 6:59 PM

 

I'm a collector that buys the games to play them.  I've bought some very rare stuff that was new and shrinkwrapped.  First thing I do is open it up and play it.  Not saying anyone is wrong to preserve sealed copies, just that it won't be me.

 

 

 

As do I, but it just worked out that way. I saw them for sale really cheap... I think I even bought a box of sealed 7800 games at the $wap $hop years ago. I just never got around to opening them and playing them. I don't really have too many video games anymore, but just never got around to it. The only thing keeping me from opening them is that I don't have a lot of time, and they're in a box in the back of the closet. :)



#937 CyranoJ ONLINE  

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Posted Thu Apr 9, 2015 7:07 PM

 
Interesting, while no deliberate blacklist, the way the bios was coded effectively locks it out.



He needs an extra 'only' as there is also a blacklist.

#938 rdemming OFFLINE  

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Posted Thu Apr 9, 2015 11:13 PM

 

JCP -B ....

 

True but then you need to start the ROM always through JCP which means you need it connected to a PC or laptop. Not ideal.



#939 CyranoJ ONLINE  

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Posted Thu Apr 9, 2015 11:27 PM

 

True but then you need to start the ROM always through JCP which means you need it connected to a PC or laptop. Not ideal.

 

Unless you patch at 8k offset with $4ef9 xxxx yyyy

 

Which, if you'd potched around enough to work out the run address wouldn't be that much of a stretch.



#940 rdemming OFFLINE  

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Posted Fri Apr 10, 2015 12:04 AM

 

Unless you patch at 8k offset with $4ef9 xxxx yyyy

 

 

And with that overwriting posibly vital bytes at that address that need to be "compensated" elsewhere  :P  Not a big deal but it is something to keep in mind.

But I thought you would not give tips on hacking ROMs to run a a Skunk :grin:



#941 CyranoJ ONLINE  

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Posted Fri Apr 10, 2015 12:16 AM

 

And with that overwriting posibly vital bytes at that address that need to be "compensated" elsewhere  :P  Not a big deal but it is something to keep in mind.

But I thought you would not give tips on hacking ROMs to run a a Skunk :grin:

 

Nah, I said I wouldn't do it for you. Feel free to take these and run with them ;)






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