Discrepancy between OpenMSX and real hardware (color palette change)

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By Manuel

Ascended (14372)

Manuel's picture

18-04-2018, 17:29

Haven't received anything...

By pipagerardo

Supporter (12)

pipagerardo's picture

18-04-2018, 18:00

Hello anybody!!! I'm the Cazurro that no speak English in the present and in the future sure that no. In this link https://github.com/pipagerardo/test_nmsxtiles they are the asunto of the question. The source code was assambled with sjasmpg https://github.com/pipagerardo/sjasmpg a fork of the sjasm assambler. The executión was over a Philiphs VG-8020/40 and too in a VG-8020/20. I hope that this little grain of sand could you help for better MSX emulator. Thanks and sorry for my Donkey English.

By pipagerardo

Supporter (12)

pipagerardo's picture

18-04-2018, 18:07

The Email fail to send, Manuel.BilderbeekREMOVE@CAPSgmail.com removing the caps of course. You can send me the correct email or prove the github link that also fail in VG8020.

By pipagerardo

Supporter (12)

pipagerardo's picture

18-04-2018, 18:36

I have problems with email gmail, in this link they are https://drive.google.com/open?id=1ld65hnRs4Ra5I9ihsdovMKkXQm...

By santiontanon

Hero (583)

santiontanon's picture

18-04-2018, 19:13

Thanks pipagerardo! The ROM in question is "test_mal.rom", right?

By santiontanon

Hero (583)

santiontanon's picture

18-04-2018, 19:38

I just had a chance to test it, and indeed in OpenMSX 0.14.0 and also in the latest fMSX colors display normally, unlike in a real MSX1 (VG8020), where they are messed up.

By Manuel

Ascended (14372)

Manuel's picture

18-04-2018, 21:49

OK, but how could they get messed up?? The code is sending data to 0x9A?

By santiontanon

Hero (583)

santiontanon's picture

18-04-2018, 22:04

That I have no idea! I'm basing all of this on the video I linked originally. Basically, Gerardo had code to change the color palette, and he naively assumed that on an MSX1 that code would get ignored. But instead, when tested in 3 of his MSX1 computers, he got that result with all the colors being blue (he says that he originally thought it was just a cable problem, but he got the same execution behavior with all 3 of his machines, and removing the palette color change code, makes the code run fine on his physical machines).

By Manuel

Ascended (14372)

Manuel's picture

18-04-2018, 22:43

The real question for me is: what happens on that real hardware that can explain this?? Note that on an MSX2 it also seems to work fine.

Perhaps it is writing by accident that VDP bit that gives the 'alternate color palette', i.e. actually the EXT_VIDEO bit?

By santiontanon

Hero (583)

santiontanon's picture

19-04-2018, 16:07

No idea! I think the only way to find out would be to create alternate versions of that ROM, playing around with that code and running it on the original hardware, until we find out what is it that is happening

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