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View topic - SMS Timings NTSC/PAL?
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Michael Montageu
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 SMS Timings NTSC/PAL?
 Posted: Tue Oct 19, 1999 12:10 am
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I'm having horrible trouble getting the timing on my SMS emulator to work very well, as none of this info seems to be clearly documented.
Does anyone know how fast the Z80 is running with regards to the 60hz of NTSC? (If there are 60 VBlanks a second, how many or cycles can the Z80 perform per VBlank?) Also, has anyone else written a complete emulator that runs native to Win9x? Maybe then I can stop mine. ;) - Mike |
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Nyef
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Posted: Tue Oct 19, 1999 12:39 am
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Oh, it's very clearly documented... In the archives of an NES mailing list. (I'm not kidding, either)
The Z80 runs at the NTSC color subcarrier frequency (3.579545 MHz). There are 262 scanlines per frame (synonymous with field, because we're non-interlaced). At 192 active lines per frame we have 262 - 192 = 70 inactive lines per frame. Feel free to assume that these are the VBlank, I do. I also worked the number of CPU cycles (T states, not M cycles) per scanline out to 227.5, for what good that does. :-) I do not have figures for a PAL system, but I may take the time to work them out based on the figures I already have and the value of XTAL1 in my PAL SMS II.
I have heard reports that DarcNES + WinAllegro is servicable.
--Nyef |
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Michael Montague
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Posted: Tue Oct 19, 1999 6:54 am
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This might show my ignorance, but do NES timings help SMS emulation? I thought the NES was a 6502/6510 varient? I don't know much about NES hardware ...
[Excellent answer cut] AWESOME! Thanks very much that is *exactly* what I was looking for. If anyone can chime in with the PAL timings I'd be interested in those as well.
NES or SMS? My main reason for writing an SMS emulator is to have a fast, free, working SMS emulator native to Win9x/NT. (So it can run in a window or full screen.) - Mike |
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JM Delgado
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Posted: Tue Oct 19, 1999 10:24 am
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Hello :)
In mu emulator Calypso, the unique difference between NTSC and PAL is the timing function I used to the automatic frameskip, 60 VBlanks in NTSC and 50 in PAL. The z80 clock is the same. You can view how to make a directX emulator in the sources of DGen, available on http://www.dtmnt.com or something else. Saludos, Jose Manuel Delgado |
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Michael Montague
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Posted: Tue Oct 19, 1999 11:13 am
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So a PAL machine is 228 Tcycles a scanline, 262 scanlines a frame, and 50 frames a second? (Given of course that only 192 scanlines are actually displayed, just like NTSC.) That would actually make sense ... Thanks for all your help! My emulation is running almost flawlessly now. The only trouble I'm having is some sprite strangeness in AstroWarrior ... - Mike |
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Posted: Tue Oct 19, 1999 9:10 pm
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Meka32 ? *hint* *hint* |
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Posted: Tue Oct 19, 1999 9:12 pm
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Wow, if it is the only trouble then I guess you got a perfect emulator - release it! :) As for Astro Warrior, well.. it take advantages of the VDP latch feature. When setting a VDP address for reading, the address is set, the value latched is a buffer, then the address is incremented. So if you set the VDP for reading and then write to it, it will actually write to address+1 |
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Michael Montague
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Re: VDP Latches [Was: SMS Timings NTSC/PAL?]
Posted: Tue Oct 19, 1999 11:55 pm
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Yeah, this isn't emulated 100% correctly by my emulator yet. Omar[MEKA] also pointed out that problem. That should be fairly easy to fix as my VDP emulation needed cleaning up anyway! I'll definatly release it once it is in a stable state, but there is so much more to add! Joystick support, sound, music, GG emulation. I guess those are the major things. I imagine I'll have a whole set of new questions when I start emulating the sound! - Mike |
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Who is that Omar ?
Posted: Wed Oct 20, 1999 9:37 am
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For your information, Omar Cornut = Zoop.
Depends if you wrap the music/sound to the Adlib (as in Master Gear) or if you want to do realtime wave synthesis (as in Meka) |
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Michael Montague
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Re: Who is that Omar ?
Posted: Wed Oct 20, 1999 10:39 am
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Wow, now I feel *REALLY* stupid!
Most likely I'll end up using wave synthesis since the target platform is Windows and there is no reliable way to access Adlib hardware specifcally. Juding by all the bugs I found tonight I still have a lot more to do. The VDP now acts properly, however I seem to have added a bug in the horizontal scrolling. That's going to be a fun bug to find, especially since it worked fine yesterday. :) -Mike |
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VDP lines..
Posted: Wed Oct 20, 1999 8:23 pm
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Hehe good luck :) Are you using a line-per-line graphic engine? |
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Michael Montague
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Re: VDP lines..
Posted: Thu Oct 21, 1999 12:12 am
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Yup! It draws each scanline every 228 T States of the Z80 and sends the appropriate interrupts. For some reason every so often my emu decides to ignore H-Scroll for a frame. Very ugly I must say. I guess if I don't find it soon I can just start by rewriting the scan line draw code. Its amazing how trying to speed up rendering can totally break that function. (static variables are your friend!) Sometime soon I'll have to send you the code so you can laugh. It's all C++ and I'm having to do so many tricks for speed its humerous. :) - Mike |
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hum :/
Posted: Thu Oct 21, 1999 1:27 pm
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I would love to understand what you all talked in this discussion :/ |
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Michael Montague
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Posted: Sat Oct 23, 1999 8:44 am
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Oh? I hadn't heard about it until you just mentioned it. How does one obtain it? - Mike |
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