About Nemesis 3 and SVI-738

Prophet (3515)

15-05-2007, 16:39

As some of you probably know, Nemesis 3 does not work on SVI-738 machines. Since Ramones got a SVI, we examined the game ROM and tried to find the bug.
If a MSX2 computer is detected, the game changes the color palette. But the problem is that in MSX1 models the call to the subrom to change the palette is also done (but there is no subROM entry call in the BIOS!) So it executes a lot of NOPs until the program counter reaches the first piece of code in the BIOS. But in the SVI BIOS there is some code at #15F (subROM entry) that causes the crash.

It seems Konami forgot to check the MSX model before calling to the subROM. So we made a IPS patch to solve the problem.

By Manuel

Ascended (19196)

15-05-2007, 17:35

So, doesn't detect MSX2, but it detects V9938 (or compatible)? And then assumes there's an MSX2 (or compatible) subROM?

By Guillian

Prophet (3515)

15-05-2007, 17:52

No, it just always assumes there is subROM. So in all machines it calls to #15F (subROM entry call) to change the palette.

By pitpan

Prophet (3153)

15-05-2007, 18:35

But supposedly it first detects if the host computer is an MSX2, right? If so, the SVI738 computed does not have an MSX2 BIOS, therefore it directly detects if there is a V9938 or higher VDP installed. Is this assumption correct? Quite a curious thing! Do we know if it works on Yamaha CMX-II 128 computers?

By Ramones

Champion (264)

15-05-2007, 19:07

No no ... pitpan

Yes, Gofer checks MSX first ... but when show Konami Logo always call to CALL SUBROM Bios Entry (015Fh). Always, in MSX1 or MSX2. In a 99,99999999% of MSX1s this entry is null ... fill with nops and one ret. Works ok. But in SVI this entry have code, and hangs MSX.

Its a Nemesis 3 bug.

By pitpan

Prophet (3153)

15-05-2007, 19:08

Great news!

Konami = loosers!

By NYYRIKKI

Enlighted (6010)

15-05-2007, 19:20

IIRC it is enough to copy first 16KB of the ROM to RAM #4000 before starting the game.

I've played Nemesis 3 cartridge on SVI-738, but it required some tweaking.

By Manuel

Ascended (19196)

16-05-2007, 19:41

So, it even doesn't use the V9938 in an MSX1 with a V9938....
And I can confirm that the game also has problems on the Yamaha CX5MII/128 (try with openMSX)...

By Ramones

Champion (264)

16-05-2007, 19:51

Yes Manuel. The game only use VDP 9938 in a MSX2 or higher.
Crash the game patched in the Yamaha? Or the original?
Please confirm this ... is really easy make a definitive Ips patch for the game.