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Old 27 June 2020, 22:45   #2561
Rotareneg
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Yeah, DRAM power off retention is typically a lot longer than people expect, especially at low temperatures, and can even lead to security issues: https://en.m.wikipedia.org/wiki/Cold_boot_attack
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Old 28 June 2020, 23:32   #2562
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I will ask one stupid question, that to be honest I didn't have back then, but I wonder if I was wrong then for being sure about the reply...

Design and expansion capabilities aside, is having an A2000, to all intends and purposes, as compatible to software as an A500?

Comparison is for "same gen" A2000 and A500. i.e. both OCS and 1.2/1.3 or both ECS and 1.3/2.0.

(note that I am fully aware of the specs of all Amiga models, but I wonder if there is some "hardware intricacy" I may miss that makes A500 "better" to run every pre-AGA title - given appropriate RAM size)

And since I opened that can of worms, can someone point me if there are lists of software (a) only running on OCS (not ECS), (b) only running on 1.2 (not 1.3).
I remember that it was rare but IT WAS a thing.

(I also remember there was a demo that could run only on 1.0 or... was it 1.1 A1000?... so consider this a bonus #3 question)
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Old 29 June 2020, 08:44   #2563
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Quote:
Originally Posted by NLS View Post
I will ask one stupid question, that to be honest I didn't have back then, but I wonder if I was wrong then for being sure about the reply...

Design and expansion capabilities aside, is having an A2000, to all intends and purposes, as compatible to software as an A500?

Comparison is for "same gen" A2000 and A500. i.e. both OCS and 1.2/1.3 or both ECS and 1.3/2.0.
Yes. You can also make the A2000 switchable between 1MB Chip and 512/512 for those ancient hardcoded warez.

Quote:
And since I opened that can of worms, can someone point me if there are lists of software (a) only running on OCS (not ECS), (b) only running on 1.2 (not 1.3).
I remember that it was rare but IT WAS a thing.
I doubt there is a comprehensive list. For old demos you can check http://arabuusimiehet.com/break/amiga/ to see about special needs.
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Old 29 June 2020, 10:53   #2564
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What's the story with using lowlevel.library in a game you're making? I believe it's only in ROM on CD32 (is it?), so is it allowed to distribute the library on floppy/ADF so it can boot on other Amigas?

Related ... if the game only needs U/D/L/R/F1 is there any point in me using lowlevel.library to read controllers anyway?
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Old 29 June 2020, 12:12   #2565
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Lowlevel.library is part of Kickstart 3.1, so many people have it but it's far from universally used. I'm not sure about distribution on disk, but I would suspect not - IIRC Commodore always required a licence for distributing Workbench parts, even if there was no fee involved, but who to ask these days is a different matter...

Indeed, I would say there's no need for it for just using the standard 1- or 2-button joystick configurations. You'll be extremely hard pushed to find any game that uses lowlevel.library and doesn't used the extended CD32 pad functionality.

Besides, even if you did want to read the CD32 pad, bit-banging the port to read the controller directly without lowlevel.library is relatively easy, and while it rules out being system-friendly, if you're already using the graphics hardware directly, chances are being system-friendly isn't a priority.
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Old 29 June 2020, 12:25   #2566
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Quote:
Originally Posted by Daedalus View Post
Lowlevel.library is part of Kickstart 3.1

Is it in the 3.1 ROM? Hmm.


I figured the rest was the case. I wrote the game code 20+ years ago and don't recall why I replaced reading the joysticks directly with using lowlevel I'm using lowlevel for reading keyboard state so maybe that was why I added it, but I have decided to cut that anyway leaving me with a minor and easily replaceable use of lowlevel.



And given that using lowlevel is causing me dev issues, as it isn't available either from ROM or loadable from disk when in the Amiga-Assembly debug environment, and probably will cause distribution issues later because Commodore, I think I have validation now for removing it altogether.


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Old 29 June 2020, 12:46   #2567
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Ah, my mistake, it's actually on disk and not in the ROM (except on the CD32 where it's in the extended ROM), but still part of the full 3.1 setup so is present on many, but definitely not all, Amigas.
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Old 30 June 2020, 14:29   #2568
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I actually do have a question I've always wanted an answer for:

How can Super Hires mode even work? Doesn't that need more bandwidth than a 15KHz signal can provide?
And on a related note: why does Super Hires always look kinda funky (even with Scandoublers)?
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Old 30 June 2020, 15:02   #2569
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Not really - the horizontal scanlines of an RGB image are essentially analogue - if your DAC and pixel clock are fast enough, you can have as many pixels across the screen as you like, limited I guess by how responsive the monitor is and how good the cables are at keeping the signal intact. 15kHz video affects the vertical resolution, since the kHz rating in this context refers to the horizontal sync, or how many lines it can output per second. Which is why PAL Superhighres is 1280x256 - vertical resolution is limited by the 15kHz output. Upping the vertical resolution while keeping the same rate of line output (15kHz) will reduce the refresh rate, hence interlace PAL effectively running at 25 Hz instead of 50Hz, and flickering horribly as a result.

As for why it looks funny, other than the ratio being way off, my guess is that the display or scandoubler isn't dealing with it properly. 1280x256 is smooth, clear and rock solid on my A1200 and 1084S, though everything looks very narrow due to the 1:4 pixel aspect ratio.
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Old 30 June 2020, 15:12   #2570
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Well, it never looks quite right on my A1200/Philips CM8833. It's almost as if half the pixels aren't really there. Same with all my other CRT's and scandoublers. It certainly doesn't like a 1280 pixel wide screen on say a 1990's PC.

Perhaps I'm just expecting too much though.
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Old 30 June 2020, 15:29   #2571
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Hmmm, half the pixels not being there is exactly what the result is of a scandoubler or monitor that is only sampling for high res pixel rates. You get the same effect in WinUAE if you have the video set to hires but choose a superhires video mode. But it should still be shown on that monitor, even if not perfectly sharp. It's possible the VGA monitors you're thinking of simply had a higher dot pitch, resulting in much sharper pixels.
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Old 30 June 2020, 15:47   #2572
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Quote:
Originally Posted by Daedalus View Post
Hmmm, half the pixels not being there is exactly what the result is of a scandoubler or monitor that is only sampling for high res pixel rates. You get the same effect in WinUAE if you have the video set to hires but choose a superhires video mode. But it should still be shown on that monitor, even if not perfectly sharp. It's possible the VGA monitors you're thinking of simply had a higher dot pitch, resulting in much sharper pixels.
I should be clearer, I don't mean they're literally not there - rather that it looks like they're not "really" there. Kinda blurred together. So maybe the dot pitch is indeed the explanation.

TBH, on my Indivision ECS/AGA (as well as a very old external scandoubler I used in the past) it still doesn't look particularly good and as I understand the documentation for the Indivisions, those particular scandoublers do sample the full Super Hires pixel range.

But, if you say it can look good then perhaps it's just an equipment issue.
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Old Yesterday, 00:24   #2573
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Just looked it up and the CM8833 has a dot pitch of 0.42 mm. That's approximately 677 pixels horizontal with that 14" CRT. If you account for the smaller visible area on the tube, it's even worse.
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Old Today, 08:50   #2574
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How can Super Hires mode even work? Doesn't that need more bandwidth than a 15KHz signal can provide?
Over chip RAM bus, you mean? Yes, that is a neat trick...


As far as the ChipMem bus is concerned, SuperHIRES is a 70ns mode with 4 bitplanes, that is, it requires as much bandwidth as a 640 pixel HIRES screen with 4 bitplanes. Thus, for each pixel, 4x4=16 bits of bitplane data is read.


Now comes the tricky part: These 16 bits go into DENISE, and it creates two pixels out of every pixel it reads. I do not quite recall how the bits are reshuffled, but essentially, if the input data for a pixel are the four bitplanes abcd, addressing one out of 16 colors, then the output are two pixels of the form ab|cd. This works because 16=4x4=2x8, i.e. 4 70ns bitplanes can provide sufficient data for 2 35ns bitplanes.


One of the side effects of this reshuffling is that you only have 2 bits to define the color in each color register. In fact, the upper 2 bits of each 4 bit color register go to one of the two pixels it generates, the lower two bits to the other pixel.


It is the graphics.library which has a "reshuffling logic" within its palette/color register loading logic to distribute the definitions of the four colors of SHires over the 16 color registers Denise needs to address a 4 bitplane HIRES mode.


Thus, twice the resolution, but half the color precision, i.e. only 64 possible colors instead of 4096.



In AGA, all this was made canonical and the "reshuffling" is no longer needed, but the chip ram bus became twice as wide, so SHIRES is a regular mode on AGA, and not a "re-intepreted HIRES mode" as it is on ECS.
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