960×540 HighRes mode

[Krashan]

I have an Amiga 1200 with Indivision AGA (Mk2, if that matters) and small 15" full HD display. I have used Xtreme (1280×1024) mode with success, adding borders around and setting 1920×1080 output mode in Indivision. However this mode has two disadvantages. First it leaves lots of display space unused. Secondly Super HighRes pixels are too small on 15" screen.

What would be ideal for me is 960×540 mode (¼ of full HD), doubled by Indivision horizontally and vertically. As Indi AGA cannot double SuperHigh Res pixels (35 ns), it has to be HighRes (70 ns mode).

My best take so far is to use PAL HighRes Laced overscanned to 540 lines and 724 pixels horizontally. Display is great, but it still leaves sides of the screen unused. Hovever it seems that PAL cannot be extended more in horizontal axis.

I guess I need to write a dedicated monitor driver then. Do you think it is possible?

[ross]

No.

Two problems, with an insurmountable one.
- the required horizontal frequency would be too low and therefore unlikely to be supported;
- Alice HTOTAL counter would overflow: 960=$3c0/$40=$F*$10+$18=$108>$FF.

This mode necessarily requires 35 ns pixels.

[Karlos]

I used to use a 1280x1024 autoscrolling 16-colour PAL laced workbench back in the day (with MagicTV and a hand curated palette). Once you got used to it, it was pretty productive. I used to use each corner of the desktop a bit like a workspace.

[Krashan]

Originally Posted by ross

Alice HTOTAL counter would overflow: 960=$3c0/$40=$F*$10+$18=$108>$FF.

I have read that HTOTAL "unit" is 280 ns, so 4 HighRes pixels. Then the whole line may have up to 255*4 = 1020 pixels. I guess the visible part of a line cannot start right from $0 also some time must be reserved for HSYNC pulse.

Maybe 960 pixels is not possible, but at least you can achieve more than 724? Leaving aside, for now, the question of whether the Indivision supports horizontal scan below 15625 Hz.

[ross]

Originally Posted by Krashan

I have read that HTOTAL "unit" is 280 ns, so 4 HighRes pixels. Then the whole line may have up to 255*4 = 1020 pixels. I guess the visible part of a line cannot start right from $0 also some time must be reserved for HSYNC pulse.

Maybe 960 pixels is not possible, but at least you can achieve more than 724? Leaving aside, for now, the question of whether the Indivision supports horizontal scan below 15625 Hz.

It's not only a problem of HSYNC or HBLANK stuff (that need to be anyway considered), but also of DMA channels used for OS/System vital support (refresh, floppy data, audio, at least one sprite..). This is the $18 in my expression.

And yes, you can display a bit more than 800 pixels without 'major' problems, but then you come up against physical limitations due to the low frequency and the DMA slots available.

EDIT: here is an example that breaks OS support, tricked HBLANK signals, the very absolute maximum ever for a standard 'PAL' system.
https://eab.abime.net/showpost.php?p...2&postcount=11
Double it for 70 ns pixels, frequency is 15625 Hz, fetch start leaving active only refresh slots.
You can lower the frequency a bit and gain some x resolution, but not much, HSYNC/HBLANK requirements would prevent you from doing it in any output device..

EDIT2: if I'm not wrong there is the SuperPlus driver for 800x600 70 ns in OS environment.
It break PAL spec and lower H/V frequencies to the maximum. Some devices don't work with it.

[Krashan]

Originally Posted by ross

It's not only a problem of HSYNC or HBLANK stuff (that need to be anyway considered), but also of DMA channels used for OS/System vital support (refresh, floppy data, audio, at least one sprite..). This is the $18 in my expression.

Makes sense. I wanted this mode for Workbench and system friendly programs, so crippling other functionality is not an option.

I have tried SuperPlus, but it turned out it cannot be properly vertically placed inside Indivision frame.

Anyway I've found some reasonable solution. If Indivision cannot double SuperHighRes pixels, let the monitor do it. I've created 960×540 HDMI output mode for Indivision, assigned it to Xtreme SuperHighRes Laced, then set this mode in ScreenMode preferences and limited screen size from 1280×1024 to 960×540. Now I have mode with 2×2 monitor pixels fitting the screen ideally. The only disadvantage is monitor adds some blur when scaling, the filter can be adjusted, but no real "nearest neighbour" mode...

[pandy71]

Not sure if this solve some problems but what if display will be in portrait mode i.e 9:16 - increasing total number of lines shouldn't be that difficult and 540 seem to be even more beneficial to system (increased H frequency).

Not sure how flexible is ECS/AGA in defining horizontal resolution...


Stupid me... of course this will not work without special translation in graphic buffer - it may be workaround for system limitations but at some point video signal must be sent as 'landscape'... not sure if Indivision can do such translation.