Advanced timing settings for Amiga

[jarp]

Hi all,

I found out that some non-PAL/NTSC resolutions Amiga can put out looks *very* bad with OSSC until some advanced settings are tweaked. Standard PAL and NTSC modes do look good but not pixel perfect. I do not fully understand how advanced timing settings do work, but I’ve found out using trial and error method that Amiga and OSSC can be made pixel perfect by setting correct samplerate and picture can be adjusted to cover overscan area also by setting H. active/synclen/backporch (useful in Workbench not so musch in gaming). However seems OSSC is hypersensitive for all this settings, i.e. sometimes some setting takes “effect” not until some other setting is changed, also I had to adjust sampling phase to get sampling just right and oh results are totally different in x3 mode than in x2 mode (when using default advanced timings it does not matter). Also when I use high resolution modes I get horizontal interference in the picture. Go figure.

Anyways Not sure if exact settings depends on individual Amiga model and revision, but decided to share the settings anyways. So here you go, please let me know if you find better settings.

Edit: Settings updated as per my later findings.

PAL:HiRes (724×284), PAL:LowRes (362×284):
240p/288p lineX3: Off
H. samplerate: 908
H. synclen: 60
H. active: 724
V. active: 284
H. backporch: 76
V. backporch: 25
Sampling phase: Adjust until you get stable and crisp picture.
Note: If V. active 284 does not work you may try 288 (PAL standard).

PAL:Super-HiRes (1440×283):
240p/288p lineX3: Off
H. samplerate: 1816
H. synclen: 72
H. active: 1440
V. active: 288
H. backporch: 198
V. backporch: 24
Sampling phase: Adjust until you get stable and crisp picture.
Note: Aspect ratio is wrong (correct one would require lineX4 support which is not there yet). But because of that mode is actually quite usable in Workbench if you have ultra widescreen monitor.

DBLPAL:High Res No Flicker (744×564), DBLPAL:Low Res No Flicker (372×564):
H. samplerate: 976
H. synclen: 96
H. active: 744
V. active: 564
H. backporch: 99
V. backporch: 10
Sampling phase: Adjust until you get stable and crisp picture.
Note: If V. active 564 does not work you may try 576 (PAL standard).

NTSC:HiRes (724×241), NTSC:LowRes (362X241):
240p/288p lineX3: Off
H. samplerate: 910
H. synclen: 60
H. active: 724
V. active: 241
H. backporch: 76
V. backporch: 16
Sampling phase: Adjust until you get stable and crisp picture.
Note: If V. active 241 does not work you may try 240 (NTSC standard).
Note: Sometimes the OSSC has troubles syncing into this mode, toggling power off and on may work.

DBLNTSC:High Res No Flicker (744X467), NTSCPAL:Low Res No Flicker (372X467):
240p/288p lineX3: Off
H. samplerate: 976
H. synclen: 20
H. active: 744
V. active: 467
H. backporch: 177
V. backporch: 74
Sampling phase: Adjust until you get stable and crisp picture.
Note: Aspect ratio is wrong (OSSC misdetects the resolution and force enables lineX2 mode). Mode may still actually be usable for Workbench use (if you have potrait monitor).
Note: Sometimes the OSSC has troubles syncing into this mode, toggling power off and on may work.

MULTISCAN:Productivity (680×495):
H. samplerate: 912
H. synclen: 96
H. active: 680
V. active: 495
H. backporch: 99
V. backporch: 12
Sampling phase: Adjust until you get stable and crisp picture.

HIGHGFX:Super-High Res (1024×384):
H. samplerate: 1304
H. synclen: 60
H. active: 1024
V. active: 384
H. backporch: 142
V. backporch: 9
Sampling phase: Adjust until you get stable and crisp picture.

HD720 (1280×360):
H. samplerate: 1576
H. synclen: 60
H. active: 1280
V. active: 360
H. backporch: 137
V. backporch: 9
Sampling phase: Adjust until you get stable and crisp picture.

-J

[BuckoA51]

Good stuff! Dblpal and productivity modes are useful for a number of games, Colonization springs to mind.

[jarp]

Huh, I think I finally fully understood how advanced timing settings do work and what each setting does. So I was able to dial in settings based on knowledge instead of trial and errors (resulting settings are more or less the same though). So here are definitive settings working on my Amiga 600 for PAL modes when using OSSC’s lineX2 mode:

PAL:HiRes, PAL:LowRes:
240p/288p lineX3: Off
H. samplerate: 908
H. synclen: 60
H. active: 724
V. active: 288
H. backporch: 77
V. backporch: 24
Sampling phase: Adjust until you get stable and crisp picture

Explanation: Amiga’s minimum resolution for PAL is 640×256 and resolution when utilizing overscan is 724×283. Using checkerboard pattern it seems H. samplerate 908 is pixel perfect setting. H. active 724 allows capturing everything Amiga outputs. V. active 288 is actually more than Amiga outputs (283), however 288 is PAL standard and may sync better than 283. As a added bonus 5 x 288 = 1440 which allows pixel perfect scaling on 1440p displays (if your display does not manage to mess it up like mine does, waiting for 5x mode…)! Backporch settings just centers the picture, adjust if yours requires different values, not sure if this depends on Amiga.

If you want to use lineX3 mode, just double H. sample rate and H. active and adjust H. backporch. Oh this allows also capturing Super-HiRes resolution (min. 1280×256 max. 1440×283) properly, lineX2 modes does not output high enough resolution for that.

PAL:HiRes, PAL:LowRes, PAL:Super-HiRes:
240p/288p lineX3: On
H. samplerate: 1816
H. synclen: 72
H. active: 1448
V. active: 288
H. backporch: 198
V. backporch: 24
Sampling phase: Adjust until you get stable and crisp picture

Super-HiRes outputs only 1440 pixels so you could reduce H. active to 1440 for it, but then you would have to re-adjust for LoRes and HiRes modes. Best to leave it to 1448 and it’s compatible with all modes.

[jarp]

Then double PAL modes…

DBLPAL:High Res No Flicker, DBLPAL:Low Res No Flicker:
H. samplerate: 976
H. synclen: 96
H. active: 744
V. active: 564
H. backporch: 100
V. backporch: 10
Sampling phase: Adjust until you get stable and crisp picture

Nothing out of ordinary here. Amiga’s min. resolution for double PAL is 640×512 and max. 744×564 when using full overscan. One could dial in V. active 540 which would result not into full overscan resultion but would be half of the 1080p and quarter of 2160p and thus pixel perfect for upscaling purposes. If your display does not sync to 564 or 540 then 576 could be tried (PAL) but that’s not pixel perfect with anything.

[jarp]

And then NTSC modes:
NTSC:HiRes, NTSC:LowRes in lineX2 mode:
240p/288p lineX3: Off
H. samplerate: 910
H. synclen: 60
H. active: 724
V. active: 241
H. backporch: 76
V. backporch: 16
Sampling phase: Adjust until you get stable and crisp picture

NTSC:HiRes, NTSC:LowRes in lineX3, NTSC:Super-HiRes mode:
240p/288p lineX3: ON
H. samplerate: 1820
H. synclen: 72
H. active: 1448
V. active: 241
H. backporch: 198
V. backporch: 16
Sampling phase: Adjust until you get stable and crisp picture

DBLNTSC:High Res No Flicker, NTSCPAL:Low Res No Flicker:
OSSC does not sync

That should be all except interlaced modes, perhaps somebody else would have energy for those 🙂 Oh and as you noticed, my settings will always show whole overscan area since I want Workbench screen to be as large as possible. For gaming you could shrink active values to match nominal resolution and backporch to center it to avoid getting black bars. Samplerate should not be modified.

[jarp]

Edited new settings to the first post. Got DBLNTSC to work as well (sometimes OSSC won’t sync and rebooting OSSC fixes it). Also slightly adjusted other settings and added comments. Ditched lineX3 settings since my settings produced either incorrect aspect ratio (Linetriple mode 16:9) or were wrong (Linetriple mode 4:3).

Perhaps somebody could do lineX3 settings but I think those lineX2 settings are as perfect as it gets.

[jarp]

Added advancaed timing settings for HighGFX modes (http://aminet.net/package/driver/moni/HighGFX40_6). The OSSC misdetectes those modes (as expected) and my monitors refuses to sync until better values have been dialed on.

Those modes are actually quite usable, e.g. HD720 mode is true 16:9 mode which scales nicely:

[jdryyz]

Hi jarp!

I sent you an email over on EAB but I guess you did not get the notification.

Does the OSSC accept the Dbl modes over SCART seeing as how they are not 15KHz? Hoping I do not have to use the VGA input for these. However, that HD720 mode looks so good, I might not care about the Dbl modes anymore. Then again, HD720 isn’t 15KHz either (but it is close). Does it slow down a lot in 16 colors (my A1200 has an ‘030 and I find 16 colors acceptable)? Your example above looks to be 4 colors.

[BuckoA51]

You can feed 31khz signals to the OSSC via SCART no problem.

[jdryyz]

Glad to hear it! In that way, I can free up the VGA input for my S-Video to VGA adapter for the C64. 🙂

Does the OSSC also do autoswitching based on which input is receiving a signal or does it require manual switching?

[jarp]

Ah sorry about delay, I am not online that often anymore… Anyways, I’d like to add to BuckoA51’s answer that at least my Amiga 600 seems to put out quite dirty and/or weak sync signals and the OSSC has troubles to sync to anything else than standard PAL no matter what LPF settings. Or perhaps Amiga goes to gensync mode, dunno. This happened with both SCART and VGA inputs.

This was fixed by using simple DIY buffered VGA adapter. I used schmitt trigger, that should clean dirty signal a bit more than just a simple buffer. Please notice that this is no fault in the OSSC since you are *supposed* to use buffered adapter with Amiga in any case (due to Amiga going to gensync mode if RGB output is loaded too much).

[BuckoA51]

Glad to hear it! In that way, I can free up the VGA input for my S-Video to VGA adapter for the C64. ?

Such things are not recommended for C64 and OSSC, you want a straight up transcoder not something that already has line-doubled the C64s output. Feeding output of such a device into the OSSC defeats the purpose of using the OSSC in the first place.

This was fixed by using simple DIY buffered VGA adapter. I used schmitt trigger, that should clean dirty signal a bit more than just a simple buffer. Please notice that this is no fault in the OSSC since you are *supposed* to use buffered adapter with Amiga in any case (due to Amiga going to gensync mode if RGB output is loaded too much).

Ah okay, can these adapters be purchased anywhere for those that don’t like soldering?

[jarp]

On Amiga related forums there are supplier who sell these DIY adapters. Commodore made these adapters back in the days but they are very hard to come by. I’ve seen adapters in eBay also, but one must take care to actually order *BUFFERED* adapter, not just straight wire adapter.

Like said, this is no fault in the OSSC. Amiga users have the same problem with VGA monitors. If monitor happens to load sync signals too much, Amiga assumes it should lock to external sync and things go downhill.

[jdryyz]

That was a quick change. So it is not a good idea to stick with straight RGB to SCART for the OSSC even though it can support the frequency ranges? Or was that just the experience you had with your A600? I will be using an A1200 with the OSSC.

jarp, I’m not sure what adapter you’re referring to but it was because of my bad experiences with Amiga RGB to VGA adapters that made me interested in the OSSC to begin with. However, I cannot confirm if I have buffered adapters or not. This is the latest one I have tried:

http://www.amibay.com/showthread.php?78792-Amiga-VIDEO-VGA-Adapters-amp-Cables-DELUXE-(real-23pin-conns)

I also have two of the Commodore brands. One of which I am using at the moment. As I have mentioned to you before in email, I see faint vertical lines on my monitor when using the adapter. The lines can almost be eliminated when in Dbl PAL HI RES NO FLICKER but I cannot adjust them out in straight PAL/NTSC hi res modes at all. The vertical lines only appear when using a VGA adapter so I know it is not my monitor.

BuckoA51,

I wasn’t sure if my idea about using the OSSC VGA input for the C64 S-Video to VGA adapter would be good or not. I was only thinking about the possibility of “passing through” the signal but still being able to add scanlines. 🙂 Perhaps I cannot have one without the other. If I will be using the OSSC’s HDMI output strictly for the Amiga, I can just use the C64 converter straight into the monitor’s VGA input. The thing about that is, the monitor’s inputs do not autoswitch and switching them is a pain.

[jdryyz]

How’s this for a buffered adapter?

http://retro.68k.pl/

(scroll down)

Includes Composite and S-Video. Doubt I would ever need that though.

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