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PostPosted: Fri Apr 21, 2017 9:03 am 
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byuu wrote:
If only someone would document that beyond the fact that it exists ... I'd love to emulate it =(


I think you can find some good (and somehow complete) technical information about it on Spritesmind, but you will have to dig a bit to find it i guess (can't find it easily right now).


Quote:
I mean, apparently there is as we're having it, but ... we can agree to disagree, I suppose.


Haha, good point you made here ;) Well honestly i think it's still quite difficult to argue the opposite but indeed we can agree or disagree.

Quote:
Don't tell that to the -nearly every game in the library- that used HDMA and per-scanline IRQs to do exactly that ... :/


I should have been more specific: outside the HDMA channels.
They are here for that but still, if you don't properly time your code and your VRAM writes goes a bit outside the VBlank period, bang ! On the MD, nothing wrong happen... you just lost a bit of time.

Quote:
And how easy it is to hard-lock the memory controller.


To be honest that happen on many old systems and probably on the SNES as well. Still if you access invalid memory area mean you probably have something really wrong in your code !

Quote:
Mode 2 on Super NES is essentially equivalent to native mode on the Genesis.


Except it works in 256px instead of 320px but Indeed it can (almost) mimic the classical Megadrive mode 5.
The point is that Mode 1, Mode 2 and Mode 7 represents about 95% of use case, other modes are almost useless and make everything much more complicated for nothing.

Quote:
Which I would find most useful for tile data decompression from ROM to VRAM.


Not only... you can also do fast 5/6 consecutive word writes per scanline without stalling the CPU which is very useful to not waste cpu time on raster effect for instance. You can also do code interlacing to improve VRAM upload capability but that is edge usable i guess ;)


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PostPosted: Fri Apr 21, 2017 9:38 am 
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Joined: Sun Sep 19, 2004 11:12 pm
Posts: 18510
Location: NE Indiana, USA (NTSC)
Stef wrote:
byuu wrote:
If only someone would document that beyond the fact that it exists ... I'd love to emulate it =(

I think you can find some good (and somehow complete) technical information about it on Spritesmind, but you will have to dig a bit to find it i guess (can't find it easily right now).

Perhaps the problem is the lack of a counterpart to https://wiki.superfamicom.org or NESdev Wiki. These can be browsed online without having to download a compressed archive to a desktop computer, decompress it using proprietary software,[1] and view it there. They can also be updated with new findings.

Stef wrote:
byuu wrote:
Don't tell that to the -nearly every game in the library- that used HDMA and per-scanline IRQs to do exactly that [access the PPU outside vblank] :/

I should have been more specific: outside the HDMA channels.

That and HDMA isn't intended for writing to VRAM. It works fine for scrolling and COLDATA but not VRAM data.

Stef wrote:
tepples wrote:
And how easy it is to hard-lock the memory controller.

To be honest that happen on many old systems and probably on the SNES as well.

The on-die memory controller of S-CPU version 1 has undefined behavior when DMA and HDMA finish at the same time, I'll admit. But otherwise, its equivalent of /DTACK, which compensates for slow WRAM, slow ROM, and extra-slow gamepad I/O, is guaranteed to release in 500 ns or so. The lack of a /DTACK timeout on the Genesis makes it even easier for a stray memory read to bring the system to an unrecoverable state.

Stef wrote:
Still if you access invalid memory area mean you probably have something really wrong in your code !

If /BERR were connected to an inverted debounced /DTACK rather than constant, a program could at least recover from an invalid memory area access to display a core dump to the developer.

Stef wrote:
The point is that Mode 1, Mode 2 and Mode 7 represents about 95% of use case, other modes are almost useless and make everything much more complicated for nothing.

Mode 3 is for title screens, and mode 5 is for high-resolution text, particularly dialogue in a story-driven game in the Japanese language.


[1] sega2f available from docs is packed in a RAR file. Unlike Zip and 7z, RAR is licensed in a way that prohibits the public from using public documentation and source code to understand the format. I'd provide more details, but the page describing what's wrong with RAR is on the Fedora project's wiki, and Red Hat is currently suffering a massive data center network outage.


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PostPosted: Fri Apr 21, 2017 10:04 am 
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Joined: Mon Mar 30, 2015 10:14 am
Posts: 171
Quote:
Perhaps the problem is the lack of a counterpart to https://wiki.superfamicom.org or NESdev Wiki. These can be browsed online without having to download a compressed archive to a desktop computer, decompress it using proprietary software,[1] and view it there. They can also be updated with new findings.

No : :wink:

https://wiki.megadrive.org/index.php?title=Main_Page

Like snes you have also an online documentation .


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PostPosted: Fri Apr 21, 2017 10:19 am 
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Joined: Sun Mar 27, 2011 10:49 am
Posts: 151
At the risk of sounding negative and discouraging what I think is a really great project and an useful step forward for the MD dev community, that wiki is...not yet good enough.

I've created an account to help, though :)


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PostPosted: Fri Apr 21, 2017 10:37 am 
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Joined: Sun Sep 19, 2004 11:12 pm
Posts: 18510
Location: NE Indiana, USA (NTSC)
From User group rights:
Users: [...] Edit pages (edit)


From Request account:
Complete and submit the following form to request a user account.

Make sure that you first read the Terms of Service before requesting an account.

Once the account is approved, you will be emailed a notification message and the account will be usable at login.


From Terms of Service:
There is currently no text in this page. You can search for this page title in other pages, or search the related logs, but you do not have permission to create this page.


I wanted to sign up there, but it asks for a biography. I don't know what details to include or exclude because "Terms of Service" is not found.

This appears to be in line with a trend where administrators of Genesis development communities require manual approval of all new accounts, such as wiki.megadrive.org, SpritesMind, and especially SonicRetro. Is there something that attracts more spammers to the Genesis?


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PostPosted: Fri Apr 21, 2017 11:05 am 
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Given how stale that wiki is, I wonder if the admin even bothers approving new accounts anymore...


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PostPosted: Fri Apr 21, 2017 11:18 am 
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tepples wrote:
I wanted to sign up there, but it asks for a biography. I don't know what details to include or exclude because "Terms of Service" is not found.


You've used so many wikis and forums before. This is seriously a stopping point for you? Just don't enter anything in the biography. Nobody is ever going to demand it from you. Nothing bad will happen to you if you do not enter a biography under this light assumption. Participating in spite of the missing ToS page is not going to jail you.


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PostPosted: Fri Apr 21, 2017 9:06 pm 
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Quick update, the zooming checkerboard demo is half way done.


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PostPosted: Fri Apr 21, 2017 9:13 pm 
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Location: Nacogdoches, Texas
I find it funny you're trying to replicate the rotozoomer of all things in that demo when you could easily do it with Mode 7. :lol:


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PostPosted: Fri Apr 21, 2017 9:22 pm 
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I'm replicating the checkerboard effect, not the mode 7 effect, even though the mode 7 effect is much more impressive.

I wonder when that write up is coming.


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PostPosted: Fri Apr 21, 2017 11:27 pm 
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mikejmoffitt wrote:
tepples wrote:
I wanted to sign up there, but it asks for a biography. I don't know what details to include or exclude because "Terms of Service" is not found.


You've used so many wikis and forums before. This is seriously a stopping point for you? Just don't enter anything in the biography. Nobody is ever going to demand it from you. Nothing bad will happen to you if you do not enter a biography under this light assumption. Participating in spite of the missing ToS page is not going to jail you.

Besides…you read their page. It's empty. You already have no point of disagreement to the stipulation set ø.


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PostPosted: Sat Apr 22, 2017 1:12 am 
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psycopathicteen wrote:
I wonder when that write up is coming.
You mean, the one posted three pages ago?


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PostPosted: Sat Apr 22, 2017 2:48 am 
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Joined: Mon Mar 30, 2015 10:14 am
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Espozo wrote:
I find it funny you're trying to replicate the rotozoomer of all things in that demo when you could easily do it with Mode 7. :lol:

I think it's good to see a guy so passionate like him for proving that snes can do wonder with his CPU even at 2.6 mhz.

But IMO, it's better to do a demo which use the snes hardware and some tricks,for doing effects that cannot be done on MD rather than monkey it .
Some effects use the MD's chunky mode, don't expect to have the same fps with planar,mostly with a 2.6 mhz 65816 CPU.


Last edited by TOUKO on Sat Apr 22, 2017 5:25 am, edited 1 time in total.

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PostPosted: Sat Apr 22, 2017 5:11 am 
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Posts: 232
I have a theoretical multi-layered Mode 7 effect that I came up with... the catch is that in order for this trick to work, some tiles must be scaled up by 2 or 4 (or if you want to go to the extreme and have four psuedo-layers worth of Mode 7, by 8). It might work its magic with a Mandelbrot set...???


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PostPosted: Sat Apr 22, 2017 7:42 am 
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Sintendo wrote:
psycopathicteen wrote:
I wonder when that write up is coming.
You mean, the one posted three pages ago?


Isn't there supposed to be another write up that explains how the effects were done?


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