#56 64kB and 16kB VRAM support for V9938

[Manuel Bilderbeek]

Some Japanese MSX machines have only 64kB VRAM. This is
not emulated at all at the moment. Also, the Yamaha
CX5MII/128 and the SVI-738 are MSX1 machines with a
V9938 built in for 80 columns in screen 0. They have
only 16kB VRAM though. So, this should be emulated as well.

[Manuel Bilderbeek]

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See this MRC topic for some information:
http://www.msx.org/forumtopic3826.html

[Manuel Bilderbeek]

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16kB VRAM has been implemented now, thanks Wouter!

64kB VRAM is probably implemented also, but it has not been
tested, because we don't have any ROMs of a machine with 64k
VRAM.

[Manuel Bilderbeek]

https://www.youtube.com/watch?v=uOT1cqKHG1c shows what happens with 64k VRAM if you try to display page 2 of screen 5. I confirmed this on a Canon V-25.

What you get on my Canon V-25 is shown in these videos:
https://www.youtube.com/watch?v=MO1SXi0JshY
and with sprites disabled:
https://www.youtube.com/watch?v=kE8JkcQBjjw

openMSX does NOT emulate this behaviour correctly. This is what you get in openMSX (a static image):

[Manuel Bilderbeek]

The following you get when executing this program in the emulated Canon V-25:

10 screen 5
20 VDP(0) = 14 : REM should enable screen 8
30 goto 30

On real Canon V-25, I get a solid green color....

See https://www.youtube.com/watch?v=TKtNpNhHIMk

Tests that l_oliveira did give different results: when trying color 15,1,1 he gets a purple screen and with 15,0,0 he gets a black screen.