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PostPosted: Wed Apr 25, 2018 8:11 am 
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Why don't we still have an aftermarket MMC5 board?
Is the repro market primarily targeted by suppliers (leaving homebrew second)?


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PostPosted: Wed Apr 25, 2018 10:04 am 
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NOOPr wrote:
Why don't we still have an aftermarket MMC5 board?

Primarily because of it's complexity. It requires a large amount of expensive hardware, and it's functionality is still not 100% known.

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Is the repro market primarily targeted by suppliers (leaving homebrew second)?

Homebrew primarily targets simpler mappers. There's only a couple homebrews to date that have utilized MMC3. I've never had a homebrewer express they're willing to spend 50% or more on boards for their homebrew game. Like it or not, but it's the repro market that has helped create the options that homebrewers now have available to them.

All that said if you have a homebrew game that utilizes MMC5 features and can communicate the specifics it makes creation of a potentially simplified board specific for your needs. It's much easier to recreate MMC5 only for your specific needs that are well known, than a 100% accurate MMC5 replica for that's not known as well.

My current boards used for MMC3/FME7 only use about half the available logic resources. They can fully decode the CPU bus, but only enough of the PPU bus to implement MMC2/4. If you can come up with a subset of MMC5 that fits in the current board design you can effectively get it for roughly the same cost as MMC3.

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PostPosted: Wed Apr 25, 2018 10:05 am 
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1- They'd be drastically more expensive for no significant market.
2- A bunch of people feel that the MMC5 stretches the capabilities too far.
2b- even with 8x8 attributes or the left-and-right split screen, you still have the limited master palette and colors-per-tile-or-sprite and sprites still can only cover 25% of the width.
3- It'd be also more expensive than just adding lots of bankswitched CHR-RAM, and that gets you most of the nice things anyway.

Once you shave away the really exceptional things the MMC5 does, it's not all that different from an MMC3/FME7/VRC4.


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PostPosted: Wed Apr 25, 2018 11:03 am 
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One thing I like about the MMC5 is that you have IRQs yet still can switch the entire CHR-ROM range with a single write. Very useful for clean screen splits and elaborate status bars with sprites in them. On the MMC3 with its stupid index register, changing the entire 8 KiB takes an eternity.


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PostPosted: Wed Apr 25, 2018 11:24 am 
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infiniteneslives wrote:
Homebrew primarily targets simpler mappers. There's only a couple homebrews to date that have utilized MMC3.

Most MegaCat titles use MMC3, it's convenient to target both for programming and for inventory.


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PostPosted: Wed Apr 25, 2018 3:10 pm 
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As I see it, this is a chicken vs. egg situation... The hardware people don't want to make a complex, expensive board since there's nothing interesting to put on it (licenced or homebrew), and programmers don't want to code MMC5 software because there's no hardware where to put it.


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PostPosted: Wed Apr 25, 2018 3:44 pm 
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tokumaru wrote:
As I see it, this is a chicken vs. egg thing... The hardware people don't want to make a complex, expensive board since there's nothing interesting to put on it (licenced or homebrew), and programmers don't want to code MMC5 software because there's no hardware where to put it.

While this is probably true for some, and it was for me previously, it's no longer the case IMO. I get requests for MMC5 rather frequently. Previously I didn't think I could make one for a reasonable price. I don't think that's the case anymore, partially due to lower prices of high density CPLD/FPGAs as year pass on. Other part of that cost reduction is a project I'm working on to dual port single port memory via time multiplexing which greatly reduces the cost (smaller CPLD/FPGA and/or removal of dedicated dual port RAM). Homebrew probably doesn't see it as a reasonable price, but I think MMC5 can be done fully assembled with memory and all for a sale price around $30 or better. So at this point for me the biggest road block is finding the development time to actually make it a reality.

I'm guessing there are a number of other people that would like to make and offer MMC5 replica boards, they're probably getting the same constant requests I do. But designing a MMC5 capable board is no easy feat, let alone on a budget. I would guess that development time/effort/skills is what's standing in most people's way that might be motivated to replicate and sell the MMC5 on a budget.

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PostPosted: Wed Apr 25, 2018 4:36 pm 
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Unless I'm mistaken, one final problem is that the MMC5 is still not 100% characterized, and hardware clones could accidentally enshrine behavior other than what the original ASIC does.

We're probably close enough, since the known weird edges (8 banks for 8x16 sprites mode and IRQ clock source) are now characterized, but ...


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PostPosted: Wed Apr 25, 2018 4:49 pm 
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infiniteneslives wrote:
I get requests for MMC5 rather frequently.

From serious developers? Where are all the cool MMC5 homebrews then? Most of the demand for MMC5 I see here in the forum comes from beginners whining about the 16x16-pixel attribute zones, which 99.9% of existing NES games adhere to.


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PostPosted: Wed Apr 25, 2018 5:00 pm 
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lidnariq wrote:
Unless I'm mistaken, one final problem is that the MMC5 is still not 100% characterized, and hardware clones could accidentally enshrine behavior other than what the original ASIC does.

I agree, but one could argue this case still exists for nearly all ASIC mappers. Part of the reason this is not fully characterized is lack of motivation and/or proper tools to do so. For example, I believe I can test the original enough to fully characterize it. But I'm not motivated nor knowledgeable enough about MMC5 behavior to determine this right now. Once I have gross functionality and better understanding of what to test exactly I'll perform necessary tests to fully characterize the original as needed. It's certainly a hurdle that needs to be overcome, but I don't see it as the primary reason it's not currently available. Either way I think we can get there without a decap, just need right combo of skills, motivation, & tools.

tokumaru wrote:
infiniteneslives wrote:
I get requests for MMC5 rather frequently.

From serious developers? Where are all the cool MMC5 homebrews then? Most of the demand for MMC5 I see here in the forum comes from beginners whining about the 16x16-pixel attribute zones, which 99.9% of existing NES games adhere to.
No, as mentioned earlier the demand doesn't start with homebrew development:
infiniteneslives wrote:
Like it or not, but it's the repro market that has helped create the options that homebrewers now have available to them.

When I very first started offering MMC3 & FME7 replicas years ago, it was the repro market that made the endeavor profitable long enough until homebrews were able take advantage of what I had to offer. Right now, I believe the biggest demand for MMC5 is that zelda hack but I'm sure there are others I don't pay that close of attention.

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PostPosted: Wed Apr 25, 2018 5:17 pm 
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I think the main alluring thing with MMC5 would be it's increased PRG and CHR size for homebrew, but INL is right in that there really is only demand for it on the repro side of things. Pretty much any homebrew can get by on MMC3.

Perhaps making a mapper based on MMC3 that offered a 8Mbit PRG and CHR would be a good thing to design, because it would satisfy the hacks that need more rom space (given that they be converted to MMC3), and could give homebrewers more room to play with as well.


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PostPosted: Wed Apr 25, 2018 5:25 pm 
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getafixx wrote:
Perhaps making a mapper based on MMC3 that offered a 8Mbit PRG and CHR would be a good thing to design

The design is rather trivial and already done supported by some emulators I believe? Just use bits 6 & 7 of the PRG bank registers and you've got support for 2MByte of PRG-ROM. I think there's some megaman hack with MMC3 that's 1MByte someone was asking me to support years ago but I've kinda forgotten about it since. In general the non-standard options I offer to homebrew developers in private discussions is turned down due to lack of emulator support despite the fact it wouldn't increase board cost.

EDIT: I neglected expanding CHR beyond 256KByte. I agree it would be nice to have a standard definition of how to do this, but it's a bit difficult esp without software. Perhaps some unused $A000/A001 bits could be used, but probably best to define 8 more registers in bank select register $8000 with unused bit 3.

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Last edited by infiniteneslives on Wed Apr 25, 2018 5:33 pm, edited 1 time in total.

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PostPosted: Wed Apr 25, 2018 5:29 pm 
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infiniteneslives wrote:
In general the non-standard options I offer to homebrew developers in private discussions is turned down due to lack of emulator support despite the fact it wouldn't increase board cost.


Why is that a bad thing? If the game wasn't supported by Flashcarts or most emulators, wouldn't that help sales in the long run as the game wouldn't be dumped and emulated within a day of selling?


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PostPosted: Wed Apr 25, 2018 5:34 pm 
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Adding support back to emulators is utterly trivial, if someone actually does release a oversize MMC3-clone image. It won't meaningfully prevent copying, but will deter development.

And I think we might accidentally have earmarked one of the random high mapper numbers to mark "MMC3 but with more PRG bank bits" to signal to ROM hackers that oversize MMC3 actually requires different hardware. Maybe?

infiniteneslives wrote:
EDIT: I neglected expanding CHR beyond 256KByte. I agree it would be nice to have a standard definition of how to do this, but it's a bit difficult esp without software. Perhaps some unused $A000/A001 bits could be used, but probably best to define 8 more registers in bank select register $8000 with unused bit 3.
IMO, I'd vote in favor of a VRC4-like or mapper 90-like CHR banking scheme.


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PostPosted: Wed Apr 25, 2018 5:39 pm 
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Quote:
Why is that a bad thing?


You still need to develop and test it with the help of emulators.

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Last edited by FrankenGraphics on Wed Apr 25, 2018 5:41 pm, edited 1 time in total.

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