What is "sync scrolling"?

[ijor]

Hi Gunstick,

What I discovered was 2 types of 0 byte lines. One which was displaying the background color, and so not increasing the screen counter. And another one was displaying nothing. A really black line (I think that's what you mean by changing sync signals) where even color 0 was not shown.

No, that's not what I meant, you can have a "black line" without altering sync. Furthermore, you can have a black line with or without increasing the screen counter (zero bytes line or not). They are not directly related.

By altering sync I mean that the timing of sync signals that go to the monitor are altered somehow. They can be altered in different ways, but the point is that they are altered or are not. Once sync is altered, you are at the mercy of the monitor/tv/capture/scan-doubler. And as long as you don't alter sync, all the tricks are kept "inside" the computer, and then you don't depend on any specific display device.

I have to say that the second VBL is a quite stable signal as long as it's not over too many lines. My old Thompson CRT was very useful for this. It shows (when you blow up brightness) all border switches in nice grey/black patterns on the right HBL. It also shows all distorted sync signals, and that 2nd VBL did nothing like this...

What this means is that this alteration of the sync signals is not fatal for most monitors, conceivable it works fine in all the CRTs at the time.

[fpgaarcade]

From my understanding of the GLUE hardware both SYNC, BLANK and DE for H and V can be modified in timing if the display mode / standard is switched at the right point. So, you can modify the timing of the SYNC signals. What effect this would have on a monitor I don't know. Certainly, if they are relying on the syncs being moved it's going to cause me no end of trouble with the DVI output.

Assuming my clone hardware runs these demos we can find out exactly what they are doing with the hardware analyser
/Mike
www.fpgaarcade.com

[ijor]

Certainly, if they are relying on the syncs being moved it's going to cause me no end of trouble with the DVI output.

They are not relying on sync being altered, they probably didn't even know it was altered. They rely only on DE not being asserted, the effect on HSYNC is just collateral damage

[fpgaarcade]

I guess most analogue monitors have a flywheel for the syncs and hence are quite tolerant to variation. My output code is not, I have to cut out a section of video for the DVI output. I have two modes, one is a multiple of the native natural screen size, the other has some overscan space built in. If the sync outputs are going to wobble around I need to find a way to stablelise the picture. mmm. Maybe use rising edge of DE for line sync or something... It's going to be interesting.

/Mike

[troed]

Sync Scrolling = hardware scroll
reason for the name "sync scrolling" coz the guys from Sync said they invented this kind of scrolling 1st on atari.

I really hope we never did We always referred to it as "hardware scrolling" and as a joint discovery between groups internally at least.

I've just read through this whole thread for the first time, it's definitely a thread for the ages! While I wrote a very early full screen (even before joining SYNC, unreleased, using purely experimental timings that probably would fail on some machines) I also know that I didn't figure out hardware scrolling myself then, that idea came later in discussions with Redhead. I did just now learn about 0-byte line vertical scrolling and 4-bit scrolling from this thread though - cool!

However, when I wrote the "About SYNC" text we had on our web page (not live for many years now) - earliest entry I can find with the wayback machine is from 1999 - I thought I had probed the brains of all members about the topics I brought up. Apparently I had it wrong though, so this post should be seen as an "I'm sorry" response to TFE's post on sync scrolling history earlier.

Talking about Swedish crews here, we must remember that SYNC, TCB and Omega had a lot of contact with eachother. A lot of demo-tricks were brainstormed by these groups - most noticeably the incredible sync-scroller (at that time referred to in Sweden as "hardware-scrolling") which was a co-operation venture between several persons (Nick/TCB, Redhead/SYNC - sorry Omega, can't remember if TFE or HAQ helped out here!)

If we ever put up another public page I'll be sure to correct the text. Sorry TFE. And when I bump into Redhead next time I'll see what has happened to his memory over the last 13 years ...

edit 2012-06-09: In preparation for a possible follow-up at some point in time I'll just note that after having gone through old source code (of the 1989 kind) and also a quick meetup with Redhead it seems it's my memory that has deteriorated. However, besides the full screens (incl. hardware scrolling) in SNYD2 and SoWatt we didn't release much else of what existed and was shown privately at parties. Credit should always go to those who did

And to the questing of who invented it first.. Well, actually... I would say that Omega and TCB invented it at the same time.
[---]
TCB however, was first to show it in a demo. I can not recall that we (Omega) ever did a demo with sync scroll...
The democrew Sync however did not have anything at all to do with the naming of the technique or its invention.

/Red Fox (later Troed) of SYNC