Strange video effect in MrGhost

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Van BiFi

Enlighted (4348)

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11-05-2004, 13:46

So all you need is a R#18, a sinustable and the time_interrupt. Hook #fd9f?Without the time interrupt. You should wait on the VDP for this one. Hook #FD9F is called every time the screen is fully built, and you don't want that right now. You want to change R#18 on every line.

Van anonymous

incognito ergo sum (116)

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11-05-2004, 14:05

BiFi: to make things clear, I am going to play MrGhost in an emulator and save it's state exactly before the mentioned effect. Which emulator(s) do you suggest to try this on ?

openMSX correctly emulates this trick.

Van [D-Tail]

Ascended (8254)

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11-05-2004, 14:07

wolf_, about that BASIC sine you mentioned, you can achieve it with
10 VDP(10)=VDP(10) XOR 1: GOTO 10

This will alternate bit0 of R#9, which is used for (Yamaha tech manual):

[(c) ASCII Corp., Nippon Gakki Co., Ltd.]

R#9
[...]
Bit0: DC : When 1, sets *DLCLK to input mode; when 0, sets *DLCLK to output mode.

Dunno what that DC-bit has gotta do with the sine effect, but the effect's very striking indeed. Try to bash down some keys while you're at it. The sine will 'walk away', because the interrupt cycle becomes longer.
Please note that this sine wave is everything except stable ^^;.

Van cax

Prophet (3736)

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11-05-2004, 14:09

Will check on openMSX.
Can blueMSX or NLMSX emulate the mentioned effects ?
Any other emulators to try ?

Van BiFi

Enlighted (4348)

afbeelding van BiFi

11-05-2004, 14:09

BiFi: to make things clear, I am going to play MrGhost in an emulator and save it's state exactly before the mentioned effect. Which emulator(s) do you suggest to try this on ?
An emulator which can do both effect and have savestates. Wink In this case I think blueMSX would be the best choice since openMSX has no save state feature (yet).

Van BiFi

Enlighted (4348)

afbeelding van BiFi

11-05-2004, 14:10

>> BiFi: to make things clear, I am going to play MrGhost in an emulator and save it's state exactly before the mentioned effect. Which emulator(s) do you suggest to try this on ?
<<
openMSX correctly emulates this trick.
Yeah, but currently lacks a save state.

Van [D-Tail]

Ascended (8254)

afbeelding van [D-Tail]

11-05-2004, 14:17

NLMSX doesn't emulate the mentioned effect (yet). Too bad, while other emulator developers are working on their product, it's quite quiet at NLMSX... Time's standing still, perhaps. NLMSX doesn't even emulate Sonyc correctly (blueMSX does nicely!)...

Van anonymous

incognito ergo sum (116)

afbeelding van anonymous

11-05-2004, 14:20

wolf_, about that BASIC sine you mentioned, you can achieve it with
10 VDP(10)=VDP(10) XOR 1: GOTO 10

Interesting, I didn't know that.

Dunno what that DC-bit has gotta do with the sine effect, but the effect's very striking indeed.
IIRC this bit has to do with the digitization capabilities of the VDP. It's probable the switching of the clock introduces a sine distortion on the sync signal.

Too bad, while other emulator developers are working on their product, it's quite quiet at NLMSX...
I've been told a new NLMSX release is near.

Van [D-Tail]

Ascended (8254)

afbeelding van [D-Tail]

11-05-2004, 15:15

wolf_, about that BASIC sine you mentioned, you can achieve it with
10 VDP(10)=VDP(10) XOR 1: GOTO 10

Ah! My bad! Don't try this, on my 8245 it tried to ruin my CRT! Use VDP(0) instead Smile
So that makes:

10 VDP(0)=VDP(0) XOR 1: GOTO 10

According to the tech manual, bit 0 of R#0 is unused! It initial value is 0, and shouldn't be changed. But if you do, and you do it fast enough, it becomes that sine routine... Big smile

Van [D-Tail]

Ascended (8254)

afbeelding van [D-Tail]

11-05-2004, 15:19

It works nice on both the NMS8245 and the FS-A1ST Smile Jolly good phun!
And try to bash down some keys then. It becomes even more phun! But actually, I don't think this trick is of interesting political value Wink...

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