MSX horizontal scolling VS NES horizontal scrolling

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By Yukio

Paragon (1540)

Аватар пользователя Yukio

16-08-2010, 03:29

Legend Keiichi 4 use statics screens for battle and when changing the screen there is a block scroll.Since the game is all made of big pixels and blocks the effect is nice ...
http://www.frieve.com/msx.html
Legend Keiichi 4 is on the FRIEVE 1993 Present Disk 2.
Download the LZH file and uncompress the content into a 3 1/2 Floppy Disk.

By flyguille

Prophet (3028)

Аватар пользователя flyguille

16-08-2010, 04:54


You are talking about MSX-1 sprite Y-coordinates 208 and 209. Smile

208 --> All sprites whose sprite plane number is bigger than sprite NN has, will disappear.

AND VDP will save a lot of extra VRAM accesses NOT reading all the SPRITE_ATT table, just stoping when it founds the value 208 (or the equivalent for msx2 screen modes).

I wonders if these extra FREED VRAM accesses, IS REALY improving the CO-VDP command's execution SPEED.


209 --> Sprite NN disappears.

By PingPong

Prophet (3901)

Аватар пользователя PingPong

16-08-2010, 17:41


I wonders if these extra FREED VRAM accesses, IS REALY improving the CO-VDP command's execution SPEED.

That's another weakly point in VDP project. All time is hard divided and there is no way to reclaim some unused memory cycles.
for example, i've done a test, while in active area i continuosly out data from z80 to VDP, while the vdp itself is doing a LMMM or HMMM command, and while sprites are on on entire screen (8 rows x 4 lines of sprites). Screen refresh is 60hz

there is no difference in vdp command execution if z80 does nothing or is outing data.
there is no difference in amount of data the z80 can push to vdp while executing or not any command.

The only difference is a small amount of gain using or not sprites, or blanking the screen.

This make me think, that VDP VRAM access arbitrer should be created more smartly, using for vdp commands the time normally used for z80 if the latter was not accessing vram.

A big speed improvement.

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