Tectoy's weird VDP behavior

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cero
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Tectoy's weird VDP behavior

Post by cero » Tue Oct 03, 2017 5:31 pm

Someone sent a video of a rom misbehaving on Tectoy's (latest) clone. It looks like DMA writes to VRAM apply correctly, but those done via the fifo/cpu interface have a massive delay. I can't find anything on this in google. Have any of you hit this?

Code: Select all

// fade out
// disable rendering
// dma new tiles in
VDP_loadTileSet(&blah, blah, 1);
VDP_waitDMACompletion();
// write new tile map
for (y = 0; y < 28; y++) {
    for (x = 0; x < 40; x++, i++) {
        VDP_setTileMapXY(PLAN_B, attr, x, y);
    }
}
// enable rendering
// fade in
Everything is written during forced blanking. It works correctly on all emulators and on genuine Sega hardware. On Tectoy's, the DMA'd tiles show correctly, but the tile map updates only appear after 60 frames/one second of writing them. That is, for the duration of the fade (half a sec) and half a sec afterwards, the new tiles are shown with the old tilemap.

The new tilemap data snaps in entirely during one frame, as if the fifo was massive, but I can't think of any reason for the delay.

cero
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Re: Tectoy's weird VDP behavior

Post by cero » Tue Oct 03, 2017 5:48 pm

Looking into "why then", there is a DMA update exactly 30 frames after the fade in (partial frame for animation, so it does not update everything). So it appears their clone buffers all cpu vram writes made during blanking, and only syncs them upon a sync point.

I'd like to find out what things it considers sync points, and what happens with cpu writes made with rendering on (in vblank or not). Anyone have such a device and a flashcart?

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Sik
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Re: Tectoy's weird VDP behavior

Post by Sik » Tue Oct 03, 2017 10:24 pm

Miniplanets will eventually crash randomly after playing for a while (you won't make it further than a few miniplanets before it crashes). Nobody knows why, and it never happens on any real console.

So huh, I'd just say to lose all hope on this because this hardware makes no sense at all.
Sik is pronounced as "seek", not as "sick".

Miquel
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Re: Tectoy's weird VDP behavior

Post by Miquel » Wed Oct 04, 2017 10:58 pm

There is inside the vpd enough memory for storing 30/40 shorts (2bytes) for several frames? No.
So it must be a program issue, then.
So watching the red ones... let me check... biological and geological data with some no so good guesses, if you allow me. I got much more the first 5 minutes, that's why we got mouths, so to speak.

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Sik
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Re: Tectoy's weird VDP behavior

Post by Sik » Thu Oct 05, 2017 2:10 am

The clone may be caching stuff for its own purposes, though. It's not real hardware (which doesn't exhibit this issue).

Actually wait, kind of confused when I try to read: the DMA'd data is transferred immediately, but not the data written manually? I wouldn't be surprised if it's stuck at VDP_waitDMACompletion() in that case. Probably the DMA flag is being reported incorrectly and it went overlooked since there's no reason to wait after a DMA transfer as the 68000 gets halted (only DMA fill and copy need you to wait for it).
Sik is pronounced as "seek", not as "sick".

cero
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Re: Tectoy's weird VDP behavior

Post by cero » Thu Oct 05, 2017 8:18 am

the DMA'd data is transferred immediately, but not the data written manually
Exactly.

The program is not stuck, since the fade happened, and the program flow continued.

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Sik
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Re: Tectoy's weird VDP behavior

Post by Sik » Thu Oct 05, 2017 4:03 pm

Oh right forgot about the fade.

OK I give up. The clone is just that trash.
Sik is pronounced as "seek", not as "sick".

Miquel
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Re: Tectoy's weird VDP behavior

Post by Miquel » Thu Oct 05, 2017 9:28 pm

ups! my mistake, is one of those "console on a chip" machines.
Knowing that you can purchase an original machine for next to nothing, is there a reason to bother ?
So watching the red ones... let me check... biological and geological data with some no so good guesses, if you allow me. I got much more the first 5 minutes, that's why we got mouths, so to speak.

cero
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Re: Tectoy's weird VDP behavior

Post by cero » Fri Oct 06, 2017 8:29 am

Distribution on the Brazilian market, since they are more common there.

Miquel
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Re: Tectoy's weird VDP behavior

Post by Miquel » Sun Oct 08, 2017 1:34 am

Do you know how Brasilian video game marked works? Is like back to the spectrum era.
So watching the red ones... let me check... biological and geological data with some no so good guesses, if you allow me. I got much more the first 5 minutes, that's why we got mouths, so to speak.

cero
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Re: Tectoy's weird VDP behavior

Post by cero » Sun Oct 08, 2017 7:48 am

As in wide piracy? Sure, but it doesn't tend to spread, and more sales are more sales. I don't count piracy as a loss for someone who wouldn't have bought in the first place either, that'd be free advertising.

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