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Re: cpc 6128 - demo [Re: Breiztiger] #115032 04/13/19 10:53 AM
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Breiztiger Offline OP
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hi

z80 test error report bug in that test

http://www.cpc-power.com/index.php?page=detail&onglet=dumps&num=12883

SCF and CCF instructions

Re: cpc 6128 - demo [Re: Breiztiger] #115033 04/13/19 11:09 AM
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Edstrom Offline
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I think this a known variant issue according to MAMEtesters: https://mametesters.org/view.php?id=2701 did you request a followup there?

Re: cpc 6128 - demo [Re: Breiztiger] #115034 04/13/19 11:16 AM
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R. Belmont Offline
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Yeah, we're emulating the NEC Z80, which in this case has that difference from the Zilog original.

Re: cpc 6128 - demo [Re: Breiztiger] #115035 04/13/19 12:13 PM
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Breiztiger Offline OP
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Sorry it seem to be that issue

Re: cpc 6128 - demo [Re: Breiztiger] #115036 04/13/19 12:21 PM
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Yeah, we're in C++ land these days tho, so creating a derived type with different behavior is far easier than 99% of what goes into MAME...

Re: cpc 6128 - demo [Re: Breiztiger] #115037 04/13/19 02:10 PM
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hap Offline
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TODO notes in z80.cpp: "This Z80 emulator assumes a ZiLOG NMOS model." (not NEC)

and regarding SCF/CCF flags: "However, people from the Speccy scene mention that SCF/CCF X/Y results are inconsistent and may be influenced by I and R registers." - so, is it wise to base NEC Z80 on SCF/CCF X/Y differences?

Re: cpc 6128 - demo [Re: Breiztiger] #115038 04/13/19 05:38 PM
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R. Belmont Offline
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The z80.cpp notes are from like 1997. I would believe the newer results from the 2018 test program over them. Also, MAME was arcade-only forever, and arcade games almost always used the NEC D780, so it's not shocking we ended up modeling it instead of Zilog.

Re: cpc 6128 - demo [Re: Breiztiger] #115039 04/13/19 05:59 PM
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hap Offline
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Those notes are old yes, more like 2008 or so.
I don't know of other NEC vs Zilog differences, but regarding SCF/CCF X/Y flags we definitely emulate the Zilog.

*edit* according to http://www.cpcwiki.eu/forum/technical-support/z80-defective-tests/ it fails on a real Zilog.

Last edited by hap; 04/13/19 06:16 PM.
Re: cpc 6128 - demo [Re: Breiztiger] #115040 04/13/19 06:39 PM
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Edstrom Offline
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Maybe a lot of arcades just starts working if we implement the NEC variation? :-)

Re: cpc 6128 - demo [Re: Breiztiger] #115041 04/13/19 07:12 PM
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No known software other than this test program cares about this difference smile

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