nametable & double buffering

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By ARTRAG

Enlighted (6515)

ARTRAG's picture

18-05-2012, 07:38

What do you mean? Have you seen the demo on real hw?

By ARTRAG

Enlighted (6515)

ARTRAG's picture

18-05-2012, 11:32

@hit9918
I expect to see sprites with y<128 flickering (only layer 0-7 are used so I double them reversing the sat at each interrupt).
I expect also to see correctly sprites with y>=128

My assumption is that cloned sprites occur at (y or 128), so if y is already >128, the clones should not appear...

According to hap's research at http://www.msx.org/forum/development/msx-development/msx1-tm...
the sprite comparator will detect a sprite at:

  1. attr_y,
  2. attr_y OR (~reg4 << 6 AND 128),
  3. attr_y OR (~reg4 << 6 AND 64),
  4. attr_y OR (~reg4 << 6 AND 192)

thus, if attr_y>128, sprites 1. and 2. should overlap and be at the right place, while 3. and 4. should be out of the screen.
where am I wrong ?

By hit9918

Prophet (2904)

hit9918's picture

18-05-2012, 13:13

My comment was just theory, also I did not have the OR in my model.

By hap

Paragon (2036)

hap's picture

18-05-2012, 14:17

i think it's preliminary, the one in meisei is more refined (yet possibly still not 100% accurate)

By ARTRAG

Enlighted (6515)

ARTRAG's picture

18-05-2012, 16:25

So, according to your latest modelling of the glitch,is my idea wrong?

By hap

Paragon (2036)

hap's picture

18-05-2012, 17:19

I don't know; it's been too long ago for me to remember the details about this glitch. Try it on meisei and also on a real MSX1.

By ARTRAG

Enlighted (6515)

ARTRAG's picture

18-05-2012, 18:13

Humm... on meisei (1.3.2) I get this strange thing:
here the screen is in normal mode, you see the software sprite multiplication in the "middle" bank, sprites in the lower bank are normal:


here instead the screen is in hybrid mode (the demo swaps modes at each scroll step), and surprisingly the sprites in the lower bank do not appear (!):

I did also a meisei video, but it is a custom file format, so I cannot upload it in youtube
Can anyone confirm this is the real HW behaviour of the TMS vdp on msx 1?
;(
;(

By hap

Paragon (2036)

hap's picture

18-05-2012, 19:17

ok, tested it on my MSX1, and it's same as meisei
http://img17.imageshack.us/img17/1350/demo44.jpg

By ARTRAG

Enlighted (6515)

ARTRAG's picture

18-05-2012, 19:24

crying.... I guess the "or 128" thing is only a part of the truth.
what is the rule that makes the last 16 sprite disappear ?

Is there any hope to workaround it ?

By hap

Paragon (2036)

hap's picture

18-05-2012, 19:32

yes, use SAT 0-7 only Crazy

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