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Rastan (Taito, 1990)
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JohnBrooks



Inscrit le: 01 Juin 2015
Messages: 4
Localisation: SF Bay area

MessagePosté le: Dim 07 Juin 2015, 7:00    Sujet du message: Répondre en citant

Regarding the backdoor, it's a way to hook code into Rastan without modifying rastan.system, rastan1, rastan2, ProDos, or patching anything in GS memory before launching Rastan.

toinet a écrit:

@John: will you post the entire source code someday?
Antoine


I'm not even sure what I have. My GS has been in a storage unit for over 20 years, so I'll have to dig it out and see what works and what is on it.

If I remember correctly, I had a version of Rastan that used an improved version of the Tomahawk GS & Hunt for Red October GS 924k disk format, and I was close to getting all of Rastan on a single disk with very fast load times.

While I thought a single-disk fast-load system would be cool and save money on floppy duplication, it wouldn't have worked as well with hard-drive install and also used more than 1 megabyte of memory, so I mothballed that version.

I also wrote two editing tools for Rastan, a tile map editor and a sprite animation editor. I'd like to see if I still have those as they were pretty general-purpose.

Another cool unreleased goodie was an intro for Hunt for Red October GS which contained an original musical score and images which (I think) were streamed off a 924k floppy on the fly. For business reasons, the intro was scrapped so the game would fit on a single floppy.

I hope this stuff is still around, but 20 years seems like a long time for magnetic media to survive.

-JB
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Mac //fx '90, Quadra 900 '91, Q900 601 PPC '94, PB G3 '97, PB G4 '01, MBP '06, rMBP '12
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qkumba



Inscrit le: 29 Jan 2012
Messages: 176

MessagePosté le: Lun 08 Juin 2015, 19:58    Sujet du message: Répondre en citant

JohnBrooks a écrit:
Regarding the backdoor, it's a way to hook code into Rastan without modifying rastan.system, rastan1, rastan2, ProDos, or patching anything in GS memory before launching Rastan.


There is no code path within rastan.system that can prevent the decompression from occurring, so I have misunderstood you at first.

However, I see that the highscores file can carry arbitrary code, called by 2/0010.
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JohnBrooks



Inscrit le: 01 Juin 2015
Messages: 4
Localisation: SF Bay area

MessagePosté le: Lun 08 Juin 2015, 20:32    Sujet du message: Répondre en citant

qkumba a écrit:
JohnBrooks a écrit:
Regarding the backdoor, it's a way to hook code into Rastan without modifying rastan.system, rastan1, rastan2, ProDos, or patching anything in GS memory before launching Rastan.


However, I see that the highscores file can carry arbitrary code, called by 2/0010.


Nice job!

Yes, that's the backdoor. When building rastan from source, it create a 'dev' highscore file with code at the end of the score data to disable protection and add in-game debug & power ups. I think there is a call to the highscore stub in the main loop for this. Or maybe the initial call to highscore patched some placeholder bytes in the main loop so the highscore 'dev' code would be called each game frame.

But yes the highscore file is both a data file and a trojan horse to insert user-code into the game. Smile

-JB
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Programmed on/for:
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Mac //fx '90, Quadra 900 '91, Q900 601 PPC '94, PB G3 '97, PB G4 '01, MBP '06, rMBP '12
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qkumba



Inscrit le: 29 Jan 2012
Messages: 176

MessagePosté le: Mar 09 Juin 2015, 1:02    Sujet du message: Répondre en citant

There's only the single call that I can see, which suggests that the dev code inserted hooks manually in order to be called again.
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toinet
Site Admin


Inscrit le: 15 Juin 2007
Messages: 3043
Localisation: Le Chesnay, France

MessagePosté le: Mar 09 Juin 2015, 6:04    Sujet du message: Répondre en citant

Very good, so the back door is now found!

En route to the 924K disk format. The "18-sec format" for 3.5" disks Wink
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JohnBrooks



Inscrit le: 01 Juin 2015
Messages: 4
Localisation: SF Bay area

MessagePosté le: Mar 09 Juin 2015, 9:08    Sujet du message: Répondre en citant

toinet a écrit:
Very good, so the back door is now found!

En route to the 924K disk format. The "18-sec format" for 3.5" disks Wink


Yes, I'll have to see if I still have that IWM R&D code. If you listen to the original Tomahawk GS or Alien Mind GS load, you can hear the rapid head stepping as the GS reads each track in a single rotation.

The 3.5" + 65816 has considerably more capability than the 5.25" + 6502 had on the //e. IIRC, the 3.5" GS IWM could store +15% to +25% more on a disk than Prodos could fit.

18 sector formats added +12.5% above dos/prodos. +25% would be equivalent to a 20 sector format on a 5.25".

-JB
_________________
Programmed on/for:
Apple ][+ '79, ][e '83, ][GS '86, SNES '90
Mac //fx '90, Quadra 900 '91, Q900 601 PPC '94, PB G3 '97, PB G4 '01, MBP '06, rMBP '12
SNES, Genesis, PSX, Dreamcast, PS2, Xbox, PS3, Xbox 360, PS4, Xbox One, PC, Linux
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