Search found 91 matches

by alien
Fri Sep 07, 2018 4:14 am
Forum: Demos - General
Topic: Parallax Distorter 2
Replies: 26
Views: 1725

Re: Parallax Distorter 2

Congratulations on your demo sigge! Very impressive first release. Funny you mention no graphics artists, Ajrarn & I were in a group "the Technocrats" but never released anything for the same reason. Then we joined up with ST Connexion and Krazy Rex & ATM gave us bitmaps to make ou...
by alien
Wed Aug 01, 2018 12:58 am
Forum: Hardware
Topic: The SECRET VIDEO MODE in an ST: 400 lines in COLOR (and with 72 Hz)!
Replies: 81
Views: 9705

Re: The SECRET VIDEO MODE in an ST: 400 lines in COLOR (and with 72 Hz)!

Random crazy thought: if one had a monitor which supported a 30Hz refresh rate... one could perhaps do this switch at some point when the screen in low/midrez ends, delay vsync and get a 16 colour 500 and some line screen. Good for displaying static pictures... 8) The fact one would only turn off ou...
by alien
Sun Jul 29, 2018 11:33 pm
Forum: Coding
Topic: Different SHIFTER versions
Replies: 65
Views: 4650

Re: Different SHIFTER versions

Here are a few quick video captures (50Hz, no sound, direct ST RGB feed). All done on same MB with -38 and re-verified to run OK with -38A. Unfortunately I didn't log the respective wakestates. PYM: Also checked with an IMP shifter on the board used above, but that one doesn't behave nice with a no...
by alien
Sun Jul 29, 2018 10:53 pm
Forum: Hardware
Topic: Beginning of very long journey
Replies: 135
Views: 8989

Re: Beginning of very long journey

Double plus good!
by alien
Thu Jul 05, 2018 11:05 pm
Forum: Coding
Topic: Different SHIFTER versions
Replies: 65
Views: 4650

Re: Different SHIFTER versions

I'd like to see the effect too. Thanks!
by alien
Sat Jan 13, 2018 4:21 am
Forum: Games - General
Topic: Enchanted Land parallax scroll
Replies: 21
Views: 3962

Re: Enchanted Land parallax scroll

An amusing fact for Troed: If I recall correctly, they actually had adaptive code to vary the timing of the the resolution/frequency switches around, just in case there was an Atari out there that had different timings. They read the video counter to see whether the desired line lengths had been obt...
by alien
Mon Oct 17, 2016 1:27 am
Forum: Coding
Topic: Quiz of the week: Single cycle accuracy code.
Replies: 18
Views: 4694

Re: Quiz of the week: Single cycle accuracy code.

Don't think there is any way. The Video Pointer at MMU is just a counter. The only other function besides incrementing is that Vsync edge provokes the higher bits to be reloaded from Vbase and the lower bits cleared. So only possible way seems to be to provoke a Vsync edge ... Interesting. We'd nee...
by alien
Sun Oct 16, 2016 6:07 pm
Forum: Coding
Topic: Quiz of the week: Single cycle accuracy code.
Replies: 18
Views: 4694

Re: Quiz of the week: Single cycle accuracy code.

For some reason, when you asked this question, it brought to mind that I always wondered whether there might be a way to change the video fetch address mid-screen. I tried to find a means in software, but never succeeded. That's something you could check when you decap/reverse-engineer the MMU. If t...
by alien
Thu Aug 18, 2016 3:01 pm
Forum: Hardware
Topic: MMU schematics WIP
Replies: 48
Views: 8364

Re: MMU schematics WIP

Btw, this is one of the problems of using a delay chain. It is variable and not completely reliable. The delay would depend on the board temperature. I wonder if this is one of the reasons of the Shifter weird issues observed depending on the warming (wake substates, as Troed call them). Might be. ...
by alien
Sun Jul 17, 2016 3:53 am
Forum: Coding
Topic: ST Chipset decap
Replies: 128
Views: 33182

Re: ST Chipset decap

Hi ijor, I'm curious whether you've had any chance to learn anything new on this topic since your last update.
by alien
Sun Jul 17, 2016 3:45 am
Forum: News & Announcements
Topic: *** R-TYPE DELUXE SOURCE CODE ***
Replies: 27
Views: 11419

Re: *** R-TYPE DELUXE SOURCE CODE ***

Thanks Bod/Stax, even though you can't read this.
by alien
Mon May 30, 2016 12:40 am
Forum: Hardware
Topic: Resourced TOS Rom
Replies: 47
Views: 9408

Re: Resourced TOS Rom

It makes sense they only got EmuTos working for monochrome mode: the Amiga can't do the type of bitplane interleaving the Atari ST uses, but there's only one bitplane in high-rez. Troed is right. Most games turn off the OS since TOS was notoriously slow. I remember using a "SoftBlitter" wh...
by alien
Mon May 30, 2016 12:03 am
Forum: Coding
Topic: ST Chipset decap
Replies: 128
Views: 33182

Re: ST Chipset decap

I may be misremembering, but I also think it didn't always work, whereas the the above code did force the Shifter to reset as I wanted reliably. Perhaps RESET only clears the IR registers at certain points? You are (partially) right! Yes, hardware reset might not perform actually a clean Shifter re...
by alien
Fri May 27, 2016 8:00 pm
Forum: Coding
Topic: ST Chipset decap
Replies: 128
Views: 33182

Re: ST Chipset decap

Ah, not exactly switches, but whole frames at each rez. I missed that. But if you can spend so much time, then it might be better to execute the RESET instruction. That is guaranteed to work. Of course, it is much more invasive as will affect things that you might prefer to avoid. I also had some &...
by alien
Fri May 27, 2016 4:09 am
Forum: Coding
Topic: ST Chipset decap
Replies: 128
Views: 33182

Re: ST Chipset decap

FWIW, here is the shifter reset code from my article:

reset_shifter:
move.l #$VBL_routine, $70.w
moveq #5,d0
loop:
move.b #1, $ffff8260.w
stop #$2300
clr.b $ffff8260.w
stop #$2300
dbra d0, loop
rts

VBL_routine:
rte
by alien
Wed May 25, 2016 5:31 pm
Forum: Demos - General
Topic: Atari Demoscene
Replies: 43
Views: 20496

Re: Atari Demoscene

Askja wrote:Hi all,

After some months of work, I just finished my giant picture with all the Atari Demoscene!

Enjoy!! :cheers:

http://undead-factory.fr/demoscene/index.html

Image


Very nice!
by alien
Sat May 14, 2016 9:36 pm
Forum: Demos - General
Topic: Now on Kickstarter: The Atari ST Anthology book volume 1
Replies: 20
Views: 14997

Re: Now on Kickstarter: The Atari ST Anthology book volume 1

Ok, Ich könnte vielleicht mit dem zweiten Teil helfen... ich könnte zB eine Verbindung herstellen mit den Franzosen, mit denen ich noch Kontakte habe. Welche Produkte populär waren, hat meiner Meinung nach mehr damit zu tun, in welchem Land man in den 90ern lebte. Hannover ist nicht in der Nähe von ...
by alien
Wed May 11, 2016 1:26 am
Forum: Demos - General
Topic: Now on Kickstarter: The Atari ST Anthology book volume 1
Replies: 20
Views: 14997

Re: Now on Kickstarter: The Atari ST Anthology book volume 1

Man sollte vielleicht nicht die Franzosen vergessen... Ziggy, Mcoder, Algernon: die erste schnelle 3D... ST-CNX: 4bit hardscroll, 6301 Programmierung, der erste MOD player auf ST das Ich kenne und der Schnellsten auf den Atari ST. Overlanders, Legacy, Oxygene, Dune, und so weiter, haben sehr schöne ...
by alien
Wed May 11, 2016 1:09 am
Forum: Coding
Topic: ATARI HDD low level info
Replies: 47
Views: 13668

Re: ATARI HDD low level info

As far as I know, the reason for using our own FDC routines instead of TOS was just that it made it much more practical to write fast loaders that can also do stable animation on the disk. The fact that you got more memory was more of a bonus :) Depended on the demo... Let's do the Twist Again, wou...
by alien
Wed May 11, 2016 1:04 am
Forum: Coding
Topic: ST Chipset decap
Replies: 128
Views: 33182

Re: ST Chipset decap

Below is a seudo simulation waveform of the 4-bit hard scroll. NOTE: the timing is not exact . This is just for the purpose of illustrating the idea of the K offset. Seudo-4bit.png The two vertical guides mark the moment that the resolution changed. First from mono to medium, then to low. Between b...
by alien
Wed May 11, 2016 12:38 am
Forum: Coding
Topic: ST Chipset decap
Replies: 128
Views: 33182

Re: ST Chipset decap

By the way, I am not completely sure that K is always the same, are we? There might be a wake up effect that could move K by half a cycle (one med rez cycle). I think we are -- my articles say K = 1, and I don't remember seeing any variation on that. By the way two: Is this very stable? I mean, it ...
by alien
Fri May 06, 2016 10:02 pm
Forum: Coding
Topic: ST Chipset decap
Replies: 128
Views: 33182

Re: ST Chipset decap

My 4 bit hardscroll had a weird feature: it was offset by k+4n pixels versus the normal beginning of a line (n = 0, 4, 8, 12). Because k wasn't 0, (but small, although I don't remember the value), one couldn't transition from high to low at the beginning of each line when n=0 (corresponding to not s...
by alien
Thu Mar 31, 2016 5:10 am
Forum: Coding
Topic: ST Chipset decap
Replies: 128
Views: 33182

Re: ST Chipset decap

ijor wrote:I will use this thread to post WIP details of my work on reverse engineering the ST custom chipset by layout inspection and analysis.


Cool! Looking forwards to reading this!
by alien
Thu Mar 31, 2016 4:21 am
Forum: Coding
Topic: Sync-tricks/fullscreen discussion
Replies: 90
Views: 25933

Re: Sync-tricks/fullscreen discussion

Another hypothesis would be that the counters are not initialized at powerup, and therefore can be in one of 4 states ... I'm curious whether you have evidence for either hypothesis. Hi Alien, That was mi initial hypothesis as well. Mainly because I HAD NO IDEA that those chips implement power-up l...
by alien
Wed Mar 23, 2016 3:43 am
Forum: Coding
Topic: Sync-tricks/fullscreen discussion
Replies: 90
Views: 25933

Re: Sync-tricks/fullscreen discussion

Each one of these chips has a two bits counter that clocks its respective process. The counters are not affected by hardware reset. This is by design because the processes are not completely stopped during Reset. The counters then are initialized at power up time only. There is no board level power...

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