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Van hit9918

Prophet (2932)

afbeelding van hit9918

22-09-2012, 20:56

@hap, what you gonna do with the split screen?

"I didn't add a sprite flickering routine, I need the sprite overflow bit for mid-screen pattern table split later."

When you always put 5 sprites at the end of the SAT.
Then you always get 5th sprite.
When it was a game sprite, it doesn't matter.
Take the sprite number and look at its Y. Then you know where the beam is.
The game sprites can be flickered as usual.

I heard there is the problem that on the real machine sometimes the status gets lost. It sounded like one looses a frame. But then, there are 15 more sprite lines to cause 5th sprite, so one rather should lose just a rasterline.

The Y positions above 192, is it known whether some of them are in the upper border?

Van Manuel

Ascended (19469)

afbeelding van Manuel

22-09-2012, 21:12


So I read ROM location 6.
And there is written 0x98. So the retargeting fails!
Well I read slot 0. That is where System ROM is supposed to be, no?

So, is the app supposed to save the slot that is selected in page 0 and assume that to be "System ROM"?
That could fix it.
Is that the answer? Is there maybe a standard citation on that one?

hit9918: I don't understand what you mean...

Van hap

Paragon (2042)

afbeelding van hap

22-09-2012, 21:20

I'll need mid-screen pattern-table split for vertically sliding in a second screen (as opposed to instantly popping it up). I think I'll just pause the game and poll the statusreg. Indeed it's possible to lose 1 rasterline if you read the statusreg at the same time the VDP sets it (some hw bug), but it's ok in this case.

Van hit9918

Prophet (2932)

afbeelding van hit9918

23-09-2012, 09:02

in the text you quoted, the question is: what is "BIOS calls", what is "System ROM".

Example. Say a VDP cartridge is in slot 1.
But I read ROM address 6 of slot 0.
I take slot 0 because that is what I thought is "the BIOS".
The address returns the 0x98 port of my internal ROM for the internal VDP, the redirection fails.

I could imagine this one:
On app start, you are supposed to save the slot position of page 0.
And that is where is "the BIOS calls", "the System ROM".

So, what I always wanted to know: where is the BIOS Big smile
Any standard citations on that one.

Van hit9918

Prophet (2932)

afbeelding van hit9918

23-09-2012, 09:03

Like, scroll up the info panel in quake console style? Big smile

One wobbeling rasterline often was seen on scanline interrupt machines.
When you even dont have a scanline counter, one wobbeling line is no shame.

Van hit9918

Prophet (2932)

afbeelding van hit9918

27-09-2012, 12:21

"(HB-F1XDJ and HB-F1XV) are known to have slow VDP access."

I wonder how THAT can happen? Someone made a 9958 clone from scratch?

"7T states delay", how to interpret this figure?
The fastest z80 can do is OUT in 12 cycles.
I heard MSX2 takes the 18 cycles outi.
So now I got to guess the 7 cycles figure is meant "add it to the outi", makes 25 cycles.
Such stuff could need mention in the wiki.

Van snout

Ascended (15187)

afbeelding van snout

27-09-2012, 12:23

@hit9918 - anyone can add and/or edit pages on the wiki, so by all means: feel free to complement the information there!

Van hit9918

Prophet (2932)

afbeelding van hit9918

27-09-2012, 13:48

I can't put it into wiki, because I don't know it.
All I can do is to say that the "7 cycles" figure is incomplete, something is missing.

Van sd_snatcher

Prophet (3659)

afbeelding van sd_snatcher

28-09-2012, 04:54


This excellent article on the MSX Assembly Page can make those things clear for you. Too sad the routines shown here are all also based on hardcoded I/O to the 98h/99h ports.

Van hit9918

Prophet (2932)

afbeelding van hit9918

29-09-2012, 19:14

it is again a claim with padding cycles.
padding specs are incomplete when not telling the IO instruction used AFTER the padding instructions.

But the 7 cycles figure seems to fit some puzzle:
I heard MSX2 can take outi. That is 18 cycles.
Look at this:

out ...
--- start counting here
7 inc de
12 out (0x98),a ;the instruction related to the padding

There is no 6 cycles instruction, padding with the 5 cycles NOP you would get below 18 cycles, so probably from there comes the 7 cycle figure.

And this should work, too:
out ...
--- start counting here
5 nop
14 out (c),a ;the instruction related to the padding

All I can make out of this issue is "on MSX2 do not go below 18 cycles (including the IO instruction after the padding instructions)".

I really wonder about the existance of a "slower VDP". I thought there is no 9938 clone VDP.
Maybe maybe the cause of the story is a PAL app crashing in the smaller blank area of NTSC mode.

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