32x "security code" reverse engineered

[ob1]

Oh my god !!!!
It's foggy, but how fast !!!
I'm still very modest : I don't have any clue about texturing. I'd go for flat shading first, then Gouraud, then .... Well, let's start with the very beggining !!!

[TmEE co.(TM)]

I won't swap my barrel of Charles Doty's ASM with 2 barrels of SNASM !!!


Anyway, SNASM doesn't run @ work (where 95% of my GEnesis job is done )

Maybe you should get XP compatible SNASM ?

[ob1]

I have Win 2000.
Where can I get one ? And SNASMSH by the way.

[Ketsuban]

SNASM68K for XP can be found at drx's site. SNASMSH2 can be found at Bart Trzynadlowski's site.

For purely 68k work, however, I recommend AS.

[TmEE co.(TM)]

I have Win 2000.
Where can I get one ? And SNASMSH by the way.

XP and 2K are practically same, XP just has little better 9x/DOS support and is not as jerky as 2K (In my experience 2K is not much better than ME).

I got SNASMSH2 from a 32x dev thing I downloaded somewhere... Can't remember. 2K/XP SNASM68K is available at Devster's site

[cdoty]

Anyway, SNASM doesn't run @ work (where 95% of my GEnesis job is done )

There's a version on Devster's site that runs fine on WinXP (and probably Win2k).

Another option is GNU 'as'. The only changes are comments and hex numbers.

[TmEE co.(TM)]

BTW, the XP version runs flawlessly on my Win98SE machine.

[ob1]

Sorry to relive a topic - again !,
but there is one line of code that I find surprising.
Just between SDER and TV Mode Check, we have

Code: Select all

    move.l	#$8802A2,$70    ; 21 FC 00 88 02 A2 00 70

If my 68k isn't too rusty, I translate this by
"write the value 0x8802a2 ... in ROM ?!"

First of all, how is it possible to write in ROM ?
Secondly, 0x70 is the offset for the Level 4 Interrupt (H INT), and 0x2a2 is the offset of the level 4 interrupt once the memory map was changed by setting ADEN. But what would be the point of copying this address ?

[srg320]

From 32X Overview, the same as in Sega CD.

Снимок.jpg (190.73 KiB) Viewed 29250 times

[ob1]

Hello @srg320, and thank you very much for you quick answer.
Are you telling me that the custom internal ROM ($00~$FF) is actually ... RAM ?

[srg320]

No, just area 0x70-0x73. Maybe it's a separate register.
The same register is in Sega СD and some games change it as needed.

[ob1]

OK I got it.
Quite new for me, but that explains a lot.
Thank you very much ^^

[ob1]

So,I've done my homework, and indeed, I can write at 0x70!!
Tested on Fusion and real (PAL) hardware.
Unfortunately, it looks like it doesn't work on Gens.
I can write 0x70, the KMod debug window tells me it has been modified,
but when H_INT happens, it looks like it goes to 8802A2 no matter what.

gens.png (15.1 KiB) Viewed 26812 times

May need to try a bit more on this point.