Interlaced screen modes

Historically RISC OS always had rather good support for interlaced modes because of its legacy of TV monitors and the like. Indeed, I think this was one of the reasons that Acorn won the NC contracts.

What’s the state of play, now? Whilst monitors are different beasts today compared with the 1990s, interlacing is still used for HDTV broadcasts and the like (1080i).

It occurred to me that whilst the xM is limited to about 30hz 1080p, that should be enough for 1080i50/60 which would be rather nice on a 1080 TV (providing good de-interlacing).

I couldn’t immediately see anything in MakeModes about this, and it may be a limitation of the OMAP video, but does anyone know the definitive situation?

I’ve just asked the question on the BeagleBoard Googlegroup. I’ll report back.

I’ve just asked the question on the BeagleBoard Googlegroup. I’ll report back.

Or, to save you some time…

No, it’s not possible to get an interlaced output from the DVI/HDMI port. DVI doesn’t support interlaced modes at all (remember that the BeagleBoard simply uses DVI signaling via an HDMI connector, rather than proper HDMI). I think the PandaBoard (which has a proper HDMI output) does support interlaced modes, but obviously we’re still quite a way away from running on that hardware.

Of course if you can live with S-Video resolution then I can give you all the interlacing you could ever wish for ;)

There is a reasonable chance of an HDTV being able to use 1080p24.

If it can’t, would they be able to cope with 1920×540@60Hz? (In the same way an old TV copes with 768×288@50Hz) Or would they display half height?

From playing with my Iyonix, I assume 960×1080@60Hz will confuse RISC OS with the pixel shape, so would be no good.

Yep, I already have a selection of (circa) 24p modes up and running. I haven’t tried 1920×540, which is back towards the interlacing thingumy, but I know that most HDTVs are extremely fussy about what you feed them. Conversely, most monitors are pretty flexible (albeit not at 24hz!). I’m trying to put together a HDTV specific set of supported modes, and 1080i is obviously a popular one. I do have a DVI-based DVD player which outputs 1080i (Oppo 970HD) but that may well be HDMI internally and just using DVI as a carrier because it was released in the era when some HDTVs were DVI only.

With the non interlaced TV modes on home computers, they didn’t have the half line in the field, which meant each field was the same, so you got progressive scan at half the resolution. 288p instead of 576i. CRT scanning circuitry was quite happy with this. The question is whether digital systems would behave the same way, or throw a wobbly, or just do their own thing.

These overscan and centering notes on the mythtv.org wiki (posted to the beagleboard.org mailing list) may be of some relevance/use here.

What’s the state of MDFs for BB display on digital TVs now?

Is it possible to get progressive scan at 1680 * 1050 or 1920 * 1080 from a BeagleBoard, specifically for display on a TV?

I’m not familiar with digital TV displays, so it’s a naive question.

Basically the video output of a BeagleBoard is designed for TVs.

This means that if you want to run at 1920 × 1080 (which is the resolution of HDTV) then it will do it at the 24Hz standard (of course if you’re an ARMini subscriber you get a MDF that takes this upto 40Hz).

If you want to run at 1680 × 1050 (which is a 16:10 not a 16:9 ratio so not a typical TV resolution) then the aforementioned MDF lets you go to 53Hz.

The reason for mentioning the refresh rates so much is that it is fairly common to find TVs that are happy with 24Hz (sometimes referred to as 24fps) but you need to be a lot more careful with computer monitors as they might not run at such a low refresh rate.

Having said that sometimes the manufacturers lie to you as I have just discovered with this monitor – according to the manual it shouldn’t do 1920 × 1200 at 29Hz but in reality it does…!

All these resolutions are progressive.

I hope this helps.

I hope this helps.

Yes, thanks, I feel duly encouraged; but…

of course if you’re an ARMini subscriber

… but I’m not. Are there any HD MDFs suitable for TV scan rates, available to the non-paying public? If so, where, please?

If you want to run at 1680 × 1050 (which is a 16:10 not a 16:9 ratio so not a typical TV resolution)

Not typical, I agree, but there have been a few models of TV, various makes, incorporating that panel size. The one in my kitchen is one example (Polaroid), although, since the upgrade at Hannington, it no longer receives the BBC multiplex because that’s now an 8k one. I regret buying it as a TV, but it makes a very good monitor for our notebooks, which often get used in the kitchen. Sorry for wandering OT.

Drop me an email, Dave. I figure an exception might be in order in your case given your help with the SD flashing code etc (smile). The ARMini scheme has several MDFs for different setups (including a HDTV specific MDF) which I’d be happy to share with you.