Amiga native frame rates

[mark_k]

This isn't specifically WinUAE-related, but...

I'm experimenting with tuning the precise frame rate of my laptop to match a real Amiga as closely as possible. (I'm modifying the EDID data used by the graphics driver. By changing the pixel clock you can vary the frame rate. And by adding an additional mode descriptor I can get the OS to allow selection between ~50Hz and ~60Hz natively, without needing to use e.g. PowerStrip in Windows. Can be done in both Linux and Windows. I can post a separate how-to guide if anyone's interested.)

There are several possible Amiga frame rates which complicates things. Each of these are different:

• PAL Amiga, PAL mode, non-interlaced, short fields
• PAL Amiga, PAL mode, non-interlaced, long fields
• PAL Amiga, PAL mode, interlaced

and the same for PAL Amiga & NTSC mode, NTSC Amiga & PAL mode, NTSC Amiga & NTSC mode.

The best 50Hz option for games/demos which are usually non-interlaced will be PAL Amiga, PAL mode, non-interlaced. In this thread it's mentioned that the Amiga system software outputs long fields for PAL non-interlaced. Is it the same for NTSC non-laced? What proportion of games/demos output short fields?

For PAL non-laced, long fields the frame rate works out at 49.9204092835Hz. For my laptop screen the closest pixel clock specifyable in EDID data is 101.32MHz, giving a frame rate of 49.9195926025Hz. Difference vs real Amiga: 0.000816681Hz. That's probably close enough; only .00001635967% difference.

[Toni Wilen]

NTSC is same, non-interlaced uses normally long fields (263 lines) + NTSC only long/short line toggle.

I think most programs that use short fields do it accidentally because they switch off interlaced mode (title) screen when current field is short

[universale]

Originally Posted by mark_k

I can post a separate how-to guide if anyone's interested.)

OH yes, it's very interesting!

[rare_j]

Hi
Another request for this how-to guide please. Very interesting.
Thanks

[onkelarie]

That sounds very interesting to say the least, I'm curious about the how-to as well

[gary]

Originally Posted by mark_k

by adding an additional mode descriptor I can get the OS to allow selection between ~50Hz and ~60Hz natively, without needing to use e.g. PowerStrip in Windows. Can be done in both Linux and Windows. I can post a separate how-to guide if anyone's interested.

Please post this how-to guide!

[mark_k]

I've been meaning to get around to it, but there's quite a lot to write up. Be sure to remind me in a couple of weeks if I still haven't got around to it.