New Online MSX emulator

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By ppeccin

Champion (375)

Аватар пользователя ppeccin

08-04-2016, 02:55

You mean in real hw?

Very strange... Maybe it has something to do with interleaving (expected for mode G7 where YJK and YAE were intended to be used).

By Manuel

Ascended (16639)

Аватар пользователя Manuel

08-04-2016, 19:45

Can you share a test program so we can fix openMSX where necessary?

By Grauw

Ascended (9071)

Аватар пользователя Grauw

08-04-2016, 19:50

I just did VDP(26)=&B00011000, VDP(27)=0..31 etc. in screen 0 width 40/80 and 1, it’s trivial to test.

By Manuel

Ascended (16639)

Аватар пользователя Manuel

08-04-2016, 20:48

Sorry, I meant the scrolling tests. The bogus mode of the YJK bit is already known to be not exact, see https://github.com/openMSX/openMSX/issues/1006

EDIT or, is that what you were talking about? :) Sorry,I don't know about the details, I'd just like to run it and compare with my own turboR.

By Grauw

Ascended (9071)

Аватар пользователя Grauw

08-04-2016, 21:03

The scrolling test is VDP(27)=0..31. OpenMSX already behaves like the real thing in screen 2-4, which was the only thing I wrote a short Basic program for to test. Only in screen 0 and 1 there is a difference, and as said, you can compare it with your turboR by just typing VDP(27)=any value in Basic.

Btw as for the YJK mode screenshots in that bug you linked, strange, that does resemble what I saw in screen 1, but I was not able to get that kind of striping in screen 0 with the YJK and YAE settings.

By ppeccin

Champion (375)

Аватар пользователя ppeccin

08-04-2016, 22:13

Well, I just decided to ignore YJK "bugs" in modes other than G7 in WMSX. Too costly to reproduce in terms of performance, and not that useful.

By ppeccin

Champion (375)

Аватар пользователя ppeccin

11-04-2016, 17:32

Guys, I have a question regarding port F3h on the MSX2+.

Its used to set VDP modes as well as some other flags.
BUT, when you write to F3h, what happens with the registers of the V9958? I mean, the same registers affected by the F3h write on the VDP have several other flags/bits that wound affect the VDP state.

Do these bits get reset to 0 when you write to F3h, or is there any special mechanism being used that can set only the relevant bits on the VDP registers while leaving the others unchanged?
I cannot find anything that could make this possible on the V9958 docs.

Thanks

By Grauw

Ascended (9071)

Аватар пользователя Grauw

11-04-2016, 19:13

ppeccin wrote:

Do these bits get reset to 0 when you write to F3h, or is there any special mechanism being used that can set only the relevant bits on the VDP registers while leaving the others unchanged?

I don’t know much about this port, but I can’t imagine it communicates with the VDP (neither read or write). All the logic involved for it to independently communicate with the VDP is just too complicated. I think it is simply a mirror memory cell set by the BIOS. Why it is not just a byte in the system area, I really have no clue.

Nor could I say what possible use it would have, the VDP registers are already mirrored in the system area, so it’s redundant. Maybe some kind of hardware would like to be kept up-to-date of the VDP mode (superimposing?), however afaik there’s no such hardware specifically for MSX2+, and everything already worked fine on MSX2.

By ppeccin

Champion (375)

Аватар пользователя ppeccin

11-04-2016, 19:16

I see... Its a good guess!

I was thinking it was provided so software apps could set the VDP mode in a single OUT, in contrast to several OUTs to write the VDP registers involved.
But as the BIOS itself writes to this port, in ADDITION to setting the VDP registers independently, I think your guess is way better than mine!

Thanks!

By NYYRIKKI

Enlighted (5541)

Аватар пользователя NYYRIKKI

11-04-2016, 20:06

AFAIK this is meant to be implemented by Video digitizer hardware so that you can use COPY SCREEN command without telling manually first what screen mode it should digitize.

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