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| Undocumented Mode 1 + 2 : Poll/Discussion
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ARTRAG
msx master
Berichten: 1592 |  Geplaatst: 26 Februari 2007, 18:48 |
Let's poll.
Who thinks this mode should be freely used for developing MSX games ?
For those who do not know what I am asking about:
http://bifi.msxnet.org/msxnet/tech/tms9918a.txt
I remember someone collected some data about how many msx users
cannot see this mode on ther HW.
What was the conclusion? |
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SLotman
msx professional
Berichten: 528 | Geplaatst: 26 Februari 2007, 19:28 |
There are already lot's of games that use it. Mostly adventure games, that use text on bottom of the screen, and graphics on middle-top... I dont see why not used it.
If some computers cant show it, too bad |
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jltursan
msx professional
Berichten: 845 | Geplaatst: 26 Februari 2007, 23:25 |
Quote:
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This mode is very much like Mode 1; the difference is that there can be three
different pattern tables, and control register #4 has a different meaning.
The pattern table now has 3 x 256 patterns; the screen is divided in three
parts (the top 8 character rows, the middle 8, the bottom 8). Each part can
use a different part of the pattern generator table (the first 256, the second
256, the last 256). The top part always uses the first 256 patterns in the PG.
Control register #4:
bit 7 - 3 : ignored
bit 2 : PG13; if set, PG = 2000h otherwise 0
bit 1 : if set, the last 8 rows use the 3rd pattern table otherwise 1st.
bit 0 : if set, the middle 8 rows use the 2nd pattern table otherwise 1st.
This undocumented mode is not available in the V9938 as far as I know.
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Funny; but in fact it works flawlessly! 
I've just re-tested some games that I believe they use the in-famous mix mode (only one set of patterns) and they work as expected on a NMS8245. The games are "Picture Puzzle" and "Stratos".
AFAIK the MSX2/2+ VDP processor are free of the common quirks of the MSX1 VDPs.
Since now, the only "fake" VDP I've found is the Toshiba T6950
Look at this [url=http://www.msxgamesbox.com/karoshi/index.php?topic=566.0]thread[/thread]
Quote:
| There are already lot's of games that use it. Mostly adventure games, that use text on bottom of the screen, and graphics on middle-top...
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Comercial ones?, do you remember the titles? |
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dvik
msx master
Berichten: 1302 | Geplaatst: 26 Februari 2007, 23:38 |
First of all, I wouldn't call this a hybrid screen mode if you're only playing with R3 and R4 (as I think this topic is talking about). The screen mode bits are the three M bits in R0 and R1. The R3 and R4 bits controls addressing and this so called hybrid mode is just plain screen 2 with mirroring (not a hybrid). You can check out this topic to see real hybride screen modes.
I'm using R4 mirroring it in the GnG port |
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dvik
msx master
Berichten: 1302 | Geplaatst: 26 Februari 2007, 23:50 |
The real hybrid modes are MSX1 only. The V9938 does not support these screen modes. My guess is that on a TMS9918, each of the M1-M3 bits controls a specific feature, like if its 1 or three parts on the screen or whether to use 40/32 chars per scanline. On V9938 I think the M bits are used more like a table lookup so the undocumented combinations are not supported at all.
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ARTRAG
msx master
Berichten: 1592 | Geplaatst: 26 Februari 2007, 23:57 |
Ok we can agree that the s.c. mode 1+2 isn't actually a new mode, but rather a way to force
mode 2 to address 3 times the same bank of tiles.
This name comes from the document from Sean Young, who was one of the first that documented it.
But now, the question stay the same how many users cannot see it ?
It seems that all the msx2 and upper support it, and, AFAIK, the large majority of msx1 models.
Is only the T6950 that misses this "mode"?
How many users have this chip in their msx, nowaday (when all of us use emulators ;-)
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dvik
msx master
Berichten: 1302 | Geplaatst: 27 Februari 2007, 00:20 |
I heard that almost all MSX1 models has a VDP that supports this mirroring. The concern I have is that I would like to use both R3 and R4 mirroring but that seems to screw up the sprites somehow. I didn't really understand how the mirroring of the sprites work.
I don't think its any problem at all assuming that all MSXes support R4 mirroring (just ignore the rare machine(s) where its not working).
Someone said that there are some problems with R3 mirroring and I would love to hear more about that (can't remember who said it, I think someone at the karoshi forum but I can't find it).
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jltursan
msx professional
Berichten: 845 | Geplaatst: 27 Februari 2007, 01:28 |
Maybe here? (url screwed up in my last post ) |
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PlainSpooky
msx friend
Berichten: 8 | Geplaatst: 27 Februari 2007, 02:16 |
I've been using this trick since 1992 on TMS99x8, v9938 and V9958 and I didn't have any problems. On early MSX emulators, it didn't work properlly, but now their bug has been solved.
Here's a sample, at MSXRio's website: http://msxrio.cipsga.org.br/files/ffym2_dsk.lha (brazilian portuguese only) |
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ARTRAG
msx master
Berichten: 1592 | Geplaatst: 27 Februari 2007, 09:32 |
Hi PlainSpooky, which program in your DSK uses the trick?
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cax
msx professional
Berichten: 1011 | Geplaatst: 27 Februari 2007, 09:57 |
I have somewhere font generation tool that saves a MSX-BASIC program with the colorful font you've created and sets the "1+2" mode. Basic thinks it's in SCREEN1, so you can even continue editing your program while being in this mode.
A lot of games and educational programs were written in USSR using this mode and the mentioned tool. Having such a symbols as building blocks you can make very compact graphical screens, and manipulating them is easy even in Basic.
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dvik
msx master
Berichten: 1302 | Geplaatst: 27 Februari 2007, 19:11 |
Sounds like its quite common to use mirroing so then I don't think its anything to worry about. I read the karoshi forum and some people doesn't really like using it but I don't think there are any good arguments not to use mirroring. I think its more interesting to use the full capacity of the MSX1 so I don't think its a problem if a few MSXes is not able to run a game using mirroring. Its like banning all MSX games that uses more than 8kB ram  |
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ARTRAG
msx master
Berichten: 1592 | Geplaatst: 27 Februari 2007, 19:23 |
I agree. I use mirroring as well, (there are tons of things that you cannot do in other ways).
I hope MSXDEV wont disqualify me
I was interested in the MSX's that do not support it (or better support it but get sprite mirroring as side effect).
a) Is the mirroring of the PCT, of the PGT or of both that generates sprite mirroring as side effect ?
b) Is sprite mirroring the only reason why mode 1+2 sould be avoided or there are some VDP's that does not support
the mirroring at all?
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dvik
msx master
Berichten: 1302 | Geplaatst: 27 Februari 2007, 19:35 |
I read the karoshi topic and my Spanish is not so good but if I understand correctly the mirroring does not work at all on some early Sony machines, HB-20P for example. On these machines it sounds like only the top 1/3 of the screen will be shown correctly. But it sounds like its not a problem on all HB-20P machines.
I'm also very interested to hear more about question a. Would be great to know the answer to these more specific questions (same as yours ARTRAG but more explicit):
1. Does PCT mirroring cause sprite mirroring side effects?
2. Does PGT mirroring cause sprite mirroring side effects?
3. Does PCT+PGT mirroring cause sprite mirroring side effects?
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dvik
msx master
Berichten: 1302 | Geplaatst: 27 Februari 2007, 19:37 |
I don't have a HB-20P but it would be interesting to see if the GnG demo also fails on the machines that failed Ramones test programs. Anyone that has one of the failing sony machines willing to give it a try?
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