NestopiaUE VRC2 H/V mirroring selection bug

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deadbody
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Re: NestopiaUE VRC2 H/V mirroring selection bug

Post by deadbody » Wed Mar 30, 2016 1:46 pm

I have plethora of VRC2/VRC4 carts, I can test anything. :D

lidnariq
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Re: NestopiaUE VRC2 H/V mirroring selection bug

Post by lidnariq » Wed Mar 30, 2016 2:04 pm

Are any of them already set up to take an EEPROM in lieu of PRG? I was originally intending on creating a set of 8 ROMs to make a set of NES 2.0 validation ROMs that would exhaustively test all 6* VRC4 variants and all three VRC2 variants. Rewriting the tests to work via hot-swapping would be more difficult if we don't have things to suspect are wrong.

* Including the pirate VRC4f variant

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Re: NestopiaUE VRC2 H/V mirroring selection bug

Post by deadbody » Wed Mar 30, 2016 2:08 pm

None of them are, currently. But...with my Irwin Quick-Grip and Hakko-808 I am positive I can produce one in under 15 minutes.

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Re: NestopiaUE VRC2 H/V mirroring selection bug

Post by *Spitfire_NES* » Wed Mar 30, 2016 6:10 pm

koitsu wrote:Makes sense. Thanks everyone! I'll file a bug report/Issue with the NestopiaUE guy to have this rectified. I'll also see about updating the nesdev wiki (for VRC2).

As for FCEUX and its weird V != 0xff quirk: if the code there is purely for VRC2 and not VRC4, then I don't know why they don't just mask off bits 7-1 and only honour bit 0. In other words, something like this would be clearer:

Code: Select all

/* Per official Konami documentation, VRC2 only implements horizontal (0) and
 * vertical (1) mirroring; only bit 0 is used.  nesdev thread confirming this fact:
 * http://forums.nesdev.com/viewtopic.php?f=3&t=13473
 */
case 0x9000:
case 0x9001: mirr = V & 0x01; Sync(); break;
Though the case statement isn't accurate -- the docs state clearly $9000-9FFF is mapped to the H/V toggle.

If the same code is used for VRC4, then I don't know what makes the V != 0xff quirk necessary; possibly there's some justification for it (maybe someone has official VRC4 documentation), but my gut feeling is there's probably a weird game that does something unexpected and it worked around whatever the oddity was. Too bad the commit history doesn't go back to when it was written -- thanks for digging into that, rainwarrior!

Edit: you summarise the situation beautifully well, lidnariq. Thanks for that. *thumbs up* :-)

P.S. -- I've run into my neighbour twice in the past 2 days, and he was supposed to come by last night to give me the translated results but didn't. I'll poke him tomorrow. He did say the Japanese wasn't hard and he more or less understood/got it all.
Hey Koitsu, So is this working in nestopia correctly? I thought lidnariq said that it was correct? I guess the C++ goo is too much to parse? :shock: It gives me fits hahaha.

EDIT** I see where he said it is incorrect with nestopia, i read it wrong.

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Re: NestopiaUE VRC2 H/V mirroring selection bug

Post by Zepper » Wed Mar 30, 2016 6:16 pm

Please, answer me ok? ^_^;;; This is iNES mapper 22, correct? The address mask should be AND F003, correct?

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Re: NestopiaUE VRC2 H/V mirroring selection bug

Post by lidnariq » Wed Mar 30, 2016 6:22 pm

The bug is only exposed in one mapper 23 game. The only way to solve this without submappers or hashes is something similar to what FCEUX's source has, where it special-cases the value of 0xFF.

It's true that VRC2 was also used in mapper 22 (and one game on mapper 25), but all of those games apparently never tickle this problem.

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Re: NestopiaUE VRC2 H/V mirroring selection bug

Post by koitsu » Sun Apr 03, 2016 10:41 pm

Neighbour dropped by tonight with translated bits from the official VRC2 docs. Plain and simple: there's really nothing in there we don't already know (in fact, I'd say the wiki is way more thorough, albeit a bit confusing). I even asked him about the serial/EEPROM capability, but there's nothing helpful/useful in the Japanese docs there either (i.e. nothing that would explain the bugs or wiring choices).

Still on my to-do list is to file an Issue with the NestopiaUE guy -- I'll get to it, don't worry, it's on my whiteboard. ;)

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Re: NestopiaUE VRC2 H/V mirroring selection bug

Post by lidnariq » Sun Apr 03, 2016 10:51 pm

Given the VRC2 clone that we found with a functioning microwire interface, I find myself wondering if it actually works. Perhaps Konami just decided that they were releasing no games where the additional cost of the EEPROM was worth only being able to save the game?

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Re: NestopiaUE VRC2 H/V mirroring selection bug

Post by Black Zero » Mon Apr 04, 2016 12:10 am

koitsu wrote: Still on my to-do list is to file an Issue with the NestopiaUE guy -- I'll get to it, don't worry, it's on my whiteboard. ;)
koitsu, you probably already got this issue in Nestopia covered and documented but if you don't I figured I'd make things easier for you and prepared this:

Image

Image

I have also attached a zip file containing 2 sates, 1 with the flying shooter part demo and 1 with Konami man in the hangar ready to take off.

Again, you may already have it covered and this is made using the Nestopia core in RetroArch.
Attachments
Wai Wai World (Japan) states.zip
(3.41 KiB) Downloaded 201 times

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koitsu
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Re: NestopiaUE VRC2 H/V mirroring selection bug

Post by koitsu » Mon Apr 04, 2016 4:16 am

Thanks for the save states -- I already have these though (specifically one before hangar take-off, and one at the very end of the game before the timer runs out). The .state files *do* work in NestopiaUE (just rename the extension from .state to .nsX appropriately).

I'll include these for rdanbrook as they'll help in verification.

The screenshots aren't all that useful, as I already demonstrated in my stream/YT videos (see links in first post) what the issues are. :-)

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Re: NestopiaUE VRC2 H/V mirroring selection bug

Post by Black Zero » Mon Apr 04, 2016 4:28 am

koitsu wrote:Thanks for the save states -- I already have these though (specifically one before hangar take-off, and one at the very end of the game before the timer runs out). The .state files *do* work in NestopiaUE (just rename the extension from .state to .nsX appropriately).

I'll include these for rdanbrook as they'll help in verification.

The screenshots aren't all that useful, as I already demonstrated in my stream/YT videos (see links in first post) what the issues are. :-)
No problem! I didn't know what you had so I took and made what I thought might be useful enable to solve this once and for all.
I'm just glad that this is gonna be solved and it works great in puNES now :-)

Image

Image

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koitsu
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Re: NestopiaUE VRC2 H/V mirroring selection bug

Post by koitsu » Mon Apr 04, 2016 4:42 am


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Re: NestopiaUE VRC2 H/V mirroring selection bug

Post by Black Zero » Mon Apr 04, 2016 4:48 am

koitsu wrote:NestopiaUE issue 172 filed: https://github.com/rdanbrook/nestopia/issues/172
Nice report :D :thumbs up:

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Re: NestopiaUE VRC2 H/V mirroring selection bug

Post by koitsu » Tue Apr 12, 2016 11:06 am

Looks like BizHawk (NesHawk) picked up the change as well: https://github.com/TASVideos/BizHawk/co ... 46edf9fdd1 -- type there refers to an integer they set, where for VRC2 type=2 and for VRC4 type=4. So they up using this variable as the mask for which bits to honour on mirroring writes (when previously it was always set to honour bits 1-0), rather than using an if/else or case statement to differentiate.

There's been positive response to this matter from lots of mainstream emulators. Thumbs up; good community involvement. Thanks everyone!

The only "flack" I've seen, which is still ongoing, is in the NestopiaUE ticket where a single individual is hellbent on trying to keep this from being fixed properly. First they advocated the same 0xFF comparison kludge as FCEUX. Now they're arguing that 4-screen (don't ask me why 4-screen is being brought up, I think they might mean 1-screen) support can't be removed because "unofficial VRC2 games use the feature" (I've asked for a list of those games because that would be helpful). If anyone here has insights or comments to make on that, I politely ask they comment in the ticket.

I've only two "intuitions" about Wai Wai world: either the $FF write is an unexpected bug (programmer error but it works by chance), or it's intentional in the sense that Konami knew they could write $FF to the mirroring register because only D0 is honoured, hence saving themselves an lda #$01. Either way, since the hardware only looks at D0, there's absolutely nothing wrong with a non-0 or non-1 write. *shrug*

Just remember one thing: mapper 23 has historically been used for 3 separate chips: VRC2b, VRC4e, and VRC4f. VRC4 supports more than just H/V-only. It's a bummer because had VRC2b not been lumped in with the VRC4e/4f variants in this manner, we wouldn't be dealing with this today.

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Re: NestopiaUE VRC2 H/V mirroring selection bug

Post by zxbdragon » Wed Apr 13, 2016 12:16 am

2016-04-13_15-12-51.png

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