Make a wish / What if : Genesis

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themrcul
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Re: Make a wish / What if : Genesis

Post by themrcul » Thu Oct 12, 2017 8:53 am

Hmm I seem to remember reading somewhere that if the Master System video mode was sacrificed, there would be enough CRAM available for more palettes, or something similar to that. Never mind!

And I definitely wouldn't want to sacrifice 320px wide mode - that is one of the killer advantages the MD has over the SNES and Turbografx.

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Re: Make a wish / What if : Genesis

Post by Sik » Thu Oct 12, 2017 4:22 pm

themrcul wrote:
Thu Oct 12, 2017 8:53 am
Hmm I seem to remember reading somewhere that if the Master System video mode was sacrificed, there would be enough CRAM available for more palettes, or something similar to that. Never mind!
Because Tiido keeps insisting that Master System compatibility eats up a lot of die space even though we have nearly no proof of how it's implemented.

The biggest issue could be the sprites I imagine (and again, we don't know how they did those - they could have figured out a way to shoehorn their rendering into the mode 5's circuit somehow), but I doubt so much about the tilemap since the VDP could just be rearranging bits from planar to packed the moment the tile is fetched and then just treat it the same as mode 5 (and we know there's some relationship between plane A and mode 4's tilemap, going by how it messes up if you touch mode 5 registers then switch back to mode 4 without clearing up that).

Other features that are prone to be given as candidates to be cut out: S/H, interlaced mode, occasionally window plane. Basically all the underused stuff, because of course we should blame Sega for not being able to see they would be underused in hindsight =P (though interlaced mode was always a dud to be fair) Also sometimes the PSG as well, because some people hate its sound.

This is precisely why I want to decap the VDP, the chop keeps being brought up all the time without any basis =P
themrcul wrote:
Thu Oct 12, 2017 8:53 am
And I definitely wouldn't want to sacrifice 320px wide mode - that is one of the killer advantages the MD has over the SNES and Turbografx.
Only SNES, the PC Engine can do better actually.
Sik is pronounced as "seek", not as "sick".

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TmEE co.(TM)
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Re: Make a wish / What if : Genesis

Post by TmEE co.(TM) » Thu Oct 12, 2017 4:38 pm

There's no sharing of VRAM access patterns (MD and SMS access patterns are night and day, SMS mode using patterns identical to real SMS VDP), no compatible data formats (everything is completely different, GFX, tilemaps, sprite list) or the rendering process (identical to real SMS in SMS mode). Not even the DACs seem to be shared. Only shared part is the CPU access interface (and some incompatibility with real SMS stems from it), some of the register bits, CRAM and HV counter. Same thing happened with TMS and SMS VDP, no compatible data formats, only some of the registers though small amount of the VRAM access patterns and rendering process seem shared (i.e VRAM refresh is done in VBL area and not during rendering). TMS modes behave exactly like real TMS chip, down to access limitations and VRAM access patterns and render process (though I'm not completely sure if line interrupts are usable or not and if HV counter is readable, I haven't tested these).

The hardware designer in me is not seeing anything but almost unrelated parts glued together. I wouldn't be surprised if die shots reveal some copy-paste from SMS VDP on MD VDP.
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Re: Make a wish / What if : Genesis

Post by Miquel » Sun Oct 15, 2017 6:52 pm

So small palette it's really hard to understand because you could sacrifice horizontal scroll memory, or use an external memory chip. Perhaps they were happy with the final result or perhaps they didn't want to go close to arcades, their big revenue back then.

One more thing nobody said, more priorities for sprites, so you can chose to be in between layers/planes already prioritized.

But the biggest mistake was on SNES: having 128KB on main memory, paged and not fully used, while only 64KB on VRAM was reckless, if they did it on reverse, could it set it very apart from any contender.

About the wide mode, I also prefer to have a bigger resolution (320x224 vs 256x224), but also notice that having a resolution of 256 inherits computing benefits like it fits on a byte, and it's a 2^n divisible number.
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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Re: Make a wish / What if : Genesis

Post by Sik » Mon Oct 16, 2017 4:26 am

Miquel wrote:
Sun Oct 15, 2017 6:52 pm
So small palette it's really hard to understand because you could sacrifice horizontal scroll memory, or use an external memory chip. Perhaps they were happy with the final result or perhaps they didn't want to go close to arcades, their big revenue back then.
Er, horizontal scroll data is stored in VRAM though. You mean vertical scroll? But it's still not large enough on its own to give up enough space for a second set of palettes.
Miquel wrote:
Sun Oct 15, 2017 6:52 pm
One more thing nobody said, more priorities for sprites, so you can chose to be in between layers/planes already prioritized.
At the time the norm was that only one layer had a priority setting while the rest were fixed. The Mega Drive was actually an improvement in comparison (allowing all layers to be adjusted to some extent).
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Re: Make a wish / What if : Genesis

Post by Miquel » Tue Oct 17, 2017 10:48 am

Yes, I meant vertical scroll instead. About the size, also you should also include the circuitry involved in doing the scroll. Anyway, the point was if you really want to increase the number of palettes you can sacrifice other things or add more chips.

Of course MD is an improvement :D, but my wish, after developing "the engine" of a game is to have more options (snes has more).

On an actual MD you have:
(--- In front ---)
Sprites (P=1)
LayerA (P=1)
LayerB (P=1)
Sprites (P=0)
LayerA (P=0)
LayerB (P=0)
(--- Back ----)

My wish is something like (or a good subset of):
(--- In front ---)
Sprites (P=4)
LayerA (P=1)
Sprites (P=3)
LayerB (P=1)
Sprites (P=2)
LayerA (P=0)
Sprites (P=1)
LayerB (P=0)
Sprites (P=0)
(--- Back ----)

The problem is, on my game, which has up to two levels (imagine a bridge which you can go under or above), on the upper one I can't put tiles over Actors.
By the way, snes Zelda also can't, but for other reasons.
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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