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Author Topic: Nes Mapper Conversion - What does it do?  (Read 2002 times)

SkyLizardGirl

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Nes Mapper Conversion - What does it do?
« on: January 26, 2020, 03:07:38 am »
I am just wondering what the Nes Mapper Conversion patches do exactly.

I am interested in understanding how these work, but i am looking online and
i don't really see an explanation as to what they actually do.
 
https://www.romhacking.net/hacks/4896/
 
^This for example, what would it do if i patched it?

And I am mostly talking about MMC Patches in general.

What do they do?
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Psyklax

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Re: Nes Mapper Conversion - What does it do?
« Reply #1 on: January 26, 2020, 06:45:32 am »
Most NES games use mappers which allow for more features. The hacks that convert games to other mappers let future hackers take advantage of these features in their hacks. You would need to be able to use assembly to do more advanced hacking to really benefit though, just messing with the levels in an editor isn't going to make any difference.

SkyLizardGirl

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Re: Nes Mapper Conversion - What does it do?
« Reply #2 on: January 26, 2020, 08:30:15 pm »
I mean what does it do though?

Does it just open up more features for those doing graphic change hacks or sound hacks?
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Disch

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Re: Nes Mapper Conversion - What does it do?
« Reply #3 on: January 26, 2020, 09:46:46 pm »
SHORT ANSWER

If you have to ask what a mapper hack does for you, then it is of absolutely no use to you.


LONG ANSWER

Personally, I think mapper hacks are a bit useless in general -- as anybody who would be able to make use of them would have little to no trouble changing the mapper on their own.

I mean what does it do though?

There are a few reasons why you'd want to change a game's mapper:

  • You want to expand the ROM, but the game is at it's current mapper's limit, so you want to switch to a mapper that supports more memory
  • You want an IRQ counter to split the screen either as a code optimization to reduce lag, or to add fancy raster effects into a game, and the game's current mapper doesn't have an IRQ counter
  • You want to rip up and redesign the game's music engine to take advantage of a mapper's extended audio channels
  • You are doing some heavy rework with how the game loads its graphics and you want finer CHR swapping control

All of these things are pretty low level shit and require a fair bit of asm knowledge.  ROM expansion is by far the easiest of the things I've listed, and even that is fairly involved.

Quote
Does it just open up more features for those doing graphic change hacks or sound hacks?

Sort of.

Yes in that a new mapper might be necessary to get some of the graphics/audio changes you want.

But not really because changing the mapper is like 0.5% of the work involved with changing a game's graphics/audio loading code.  It's like step 1 of 200.  Again, I frankly don't think these hacks are very useful to anyone other than the person who made them.  But I've been wrong before.

SkyLizardGirl

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Re: Nes Mapper Conversion - What does it do?
« Reply #4 on: January 27, 2020, 01:17:51 am »
Ok thank you, that's everything i needed to know.

I got it now.

I was just really unsure if i was missing something about these programs or features, so i was asking because i was concerned, i am just really interested in hacking lately.

Thank you guys.*
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Cyneprepou4uk

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Re: Nes Mapper Conversion - What does it do?
« Reply #5 on: January 28, 2020, 05:12:11 am »
Quote
You want an IRQ counter to split the screen either as a code optimization to reduce lag

And how does split screen reduce lags exactly?
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never-obsolete

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Re: Nes Mapper Conversion - What does it do?
« Reply #6 on: January 28, 2020, 05:51:56 am »
By removing the need for timed loops or waiting for sprite0 to hit in order to perform the split at a constant scanline.

Disch

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Re: Nes Mapper Conversion - What does it do?
« Reply #7 on: January 28, 2020, 10:32:39 am »
+1 to never-obsolete.

Only real way to split the screen without an IRQ is with sprite-0 hit, and it's horribly inefficient to do so because you have to have the CPU do a hard spin lock, potentially burning several scanlines worth of CPU time.

Cyneprepou4uk

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Re: Nes Mapper Conversion - What does it do?
« Reply #8 on: January 28, 2020, 05:06:54 pm »
Seems I've misunderstood, I thought you had some interesting magic trick up your sleeve to reduce lags by using split screen itself.

And it's just replacing sprite0 hit with IRQ. Boring  :D
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PolishedTurd

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Re: Nes Mapper Conversion - What does it do?
« Reply #9 on: January 31, 2020, 01:03:54 pm »
I mean what does it do though?

Does it just open up more features for those doing graphic change hacks or sound hacks?
More knowledgeable folks have answered, but the high level version for basic hacking purposes is that a more advanced mapper allows a game to use more memory (for graphics, code, data, sound, etc.) while potentially making other kinds of things possible under the hood. If you think of a processor as a desk, the books you can fit on the desk at any given time represent the amount of memory the chip can work with (call it one page). A game happens one frame at a time, during which the processor has many cycles to compute what should happen in the next frame. A memory mapper allows you to swap other pages of memory in this interstitial time, such that you have the illusion of a large memory. As if you have a vast desk that can hold dozens of books from the library open at once. Even though all those books would never fit on the desk at once, if you swap them out fast enough, it is as if they do.

The MMC5 is a powerhouse, released near the end of the NES run. Sadly, its potential was not realized. In addition to having "a lot" of addressable memory, there are additional sound channels for music and effects, a dedicated multiplication register that yields the answer as fast as you can read it back, 1K of RAM available to you all the time without swapping pages (enough to fit all the custom logic I've written for any NES hack I've worked on)... A marvelous beast. I wish NES developers had continued to work with it at the height of their game, but the market moved on.

Dracula X

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Re: Nes Mapper Conversion - What does it do?
« Reply #10 on: January 31, 2020, 01:47:44 pm »
You can also swap the code from a fixed bank to another bank like I was able to do that in The Guardian Legend for example. This is the reason why I start doing this.