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Mirroring Font ROM bits and other CGA questions #81874
09/29/12 02:55 PM
09/29/12 02:55 PM
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alt-x Offline OP
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Trying to add Poisk-1 (aka Poisk/Поиск) emulation to MESS. Here are some questions:
- are there any non MC6845 based CGA implementations in MESS which emulate pulling NMI when MC6845 ports are accessed? It looks like Amstrad XT (PC1512 or PC20) could have been a one, but is implemented via extending MC6845 capabilities. Or am I missing something?
- There is a symgen.rom containing some fonts. Original Poisk-1 didn't have an external CGA, so it must be coming from some unofficial modification.
To get things started I tried using pccga with symgen.rom, but it's showing all the symbols mirrored. Is there a standard way to mirror (Font-)ROM bits in MESS?
Tried playing with MCFG_GFXDECODE - but that's probably not the droid I'd be looking for?

Re: Mirroring Font ROM bits and other CGA questions [Re: alt-x] #81878
09/29/12 05:47 PM
09/29/12 05:47 PM
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judge Offline
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That sounds like the video worked quite different compared to regular cga cards. You're probably better off creating a separate implementation for the poisk-1 video.

Re: Mirroring Font ROM bits and other CGA questions [Re: judge] #81879
09/29/12 06:07 PM
09/29/12 06:07 PM
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Originally Posted By judge
That sounds like the video worked quite different compared to regular cga cards. You're probably better off creating a separate implementation for the poisk-1 video.


It certainly worked quite different, but at a first sight so did the Amstrad XT (PC1512) and ibm5550. Are they emulated as regular MC6845 Cards?

Re: Mirroring Font ROM bits and other CGA questions [Re: alt-x] #81881
09/30/12 08:34 AM
09/30/12 08:34 AM
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Talking about CGA, here's a small post detailing CGA memory waitstates:
http://www.reenigne.org/blog/the-cga-wait-states/

might be interesting for future reference...

-Darkstar

Re: Mirroring Font ROM bits and other CGA questions [Re: alt-x] #81883
09/30/12 12:52 PM
09/30/12 12:52 PM
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R. Belmont Offline
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My understanding is we don't emulate the PC1512 or ibm5550 yet, likely because of the lack of this NMI setup (the PC1512 is GAME_NOT_WORKING). It's of course trivial to pull NMI when CGA ports are accessed, but I don't know how well documented those schemes are.

If you're using a font ROM with the bits mirrored, your best bet is to just use a different drawing routine that compensates. And as Judge suggested, trying to tie these implementations up with the existing CGA code will just lead to pain, suffering, and someone having to rewrite the whole thing to separate them later anyway. (Or at least a sternly-worded patch rejection ;-)

Re: Mirroring Font ROM bits and other CGA questions [Re: R. Belmont] #81888
09/30/12 04:55 PM
09/30/12 04:55 PM
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John Elliott Offline
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The PC1512 doesn't do the NMI thing (it has a partial 6845 emulation that always outputs 200 lines). The PPC512 and PC20 are the ones with the NMI. It's all documented in their respective technical manuals.

Re: Mirroring Font ROM bits and other CGA questions [Re: alt-x] #81890
09/30/12 06:14 PM
09/30/12 06:14 PM
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Curt Coder Offline
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And PC1512 v1 and v2 should be fully working in MESS currently... v3 and PC1640 aren't.

Re: Mirroring Font ROM bits and other CGA questions [Re: alt-x] #81891
09/30/12 09:10 PM
09/30/12 09:10 PM
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R. Belmont Offline
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Well, all pc1512s are marked GAME_NOT_WORKING so if that's false, please change the flag smile

Re: Mirroring Font ROM bits and other CGA questions [Re: R. Belmont] #81892
10/01/12 06:28 AM
10/01/12 06:28 AM
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Originally Posted By R. Belmont
Well, all pc1512s are marked GAME_NOT_WORKING so if that's false, please change the flag smile


pc1512 and pc1512v2 are marked GAME_SUPPORTS_SAVE, not not working smile

Re: Mirroring Font ROM bits and other CGA questions [Re: alt-x] #81893
10/01/12 12:25 PM
10/01/12 12:25 PM
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R. Belmont Offline
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You're right, I was looking at amstr_pc.c where non-insane people expect to find Amstrad PCs. My mistake ;-)


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