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Re: 6€ MCE2VGA replacement - CGA/EGA/HGC capture with logic analyzer

Posted on 2020-07-18, 21:31

in Marvin \ Video

in Marvin \ Video

The fantastic news is that the code from root42 (yesterdays revision...) is running real-time at 16 MHz sample frequency.! Therefore this already works for MDA and Hercules which uses 16 MHz. That makes me confident that it will be fast enough for 24MHz with a few additional optimizations. Since …

Re: 6€ MCE2VGA replacement - CGA/EGA/HGC capture with logic analyzer

Posted on 2020-07-18, 19:28

in Marvin \ Video

in Marvin \ Video

the OSSC has a DE-15 input that supports RGBHV and RGBS - why use trash like SCART? Because virtually every TV set built between the late 1980s and the early 2010s has it? (from our European perspective) It is by far the easiest way to feed a 15kHz RGB signal into a TV set. Be careful - a passive …

Re: 6€ MCE2VGA replacement - CGA/EGA/HGC capture with logic analyzer

Posted on 2020-07-18, 12:54

in Marvin \ Video

in Marvin \ Video

I believe that the initial "phase" value should always be positive with this exact algorithm. The adjustments using the cursor keys are indeed minimal, probably too minimal. You'd have to press a key several thousand times to see a noticeable difference. Oh, I tried with phase*pclk or phase += 1000 …

Re: 6€ MCE2VGA replacement - CGA/EGA/HGC capture with logic analyzer

Posted on 2020-07-18, 10:39

in Marvin \ Video

in Marvin \ Video

So the overdraw is removed, and I tried to incorporate the phase adjustment. I tried different positions for it, I also adjusted pclk to use the same factor as Predator99's formula (319/1070). But the jitter is there, so my sampling grid due to the error accumulation is not fitting the samples …

Re: 6€ MCE2VGA replacement - CGA/EGA/HGC capture with logic analyzer

Posted on 2020-07-17, 20:50

in Marvin \ Video

in Marvin \ Video

Smells like a stray pointer issue, if you ask me. Possibly triggered by an unexpected input signal.

Re: Best CGA & Hercules games

Posted on 2020-07-17, 20:49

in Marvin \ Software

in Marvin \ Software

Judging by the screenshots, it does Hercules graphics the cheap way, though. That looks like CGA hardware emulation using the infamous customized 640x300 mode. It's obviously impossible to tell from the pictures whether it uses segment b000h or b800h, so it could be either.

Re: 6€ MCE2VGA replacement - CGA/EGA/HGC capture with logic analyzer

Posted on 2020-07-17, 20:44

in Marvin \ Video

in Marvin \ Video

Of course the compiler optimizes. It does not usually change your algorithm, though. I totally agree that buffering the input would make sense, ideally in a ring buffer big enough that it definitely contains one full line. As far as the scaling is concerned, this might then already be the full …

Re: 6€ MCE2VGA replacement - CGA/EGA/HGC capture with logic analyzer

Posted on 2020-07-17, 14:50

in Marvin \ Video

in Marvin \ Video

Of course the compiler optimizes. It does not usually change your algorithm, though. I totally agree that buffering the input would make sense, ideally in a ring buffer big enough that it definitely contains one full line. As far as the scaling is concerned, this might then already be the full …

Re: Changing VGA ROM Fonts

Posted on 2020-07-17, 14:06

in Marvin \ Video

in Marvin \ Video

I used that method for some time back in the 90s. Lately I've been using FONTEDIT and even lately Fontraption to make executable .COM files that would load my custom fonts at AUTOEXEC.BAT runtime. But then I decided to jump to next step, while freeing up 4K in the UMA, used by the font replacement …

Re: 6€ MCE2VGA replacement - CGA/EGA/HGC capture with logic analyzer

Posted on 2020-07-17, 13:57

in Marvin \ Video

in Marvin \ Video

Yes, it currently saturates one core more or less. Storing a whole frame is too much. Storing one line, yes, that would make sense and is how e.g. the OSSC works as well. Otherwise you also get higher lag, which will be significant anyway due to the complexity of the whole process. My plan is to …

Re: Changing VGA ROM Fonts

Posted on 2020-07-17, 11:24

in Marvin \ Video

in Marvin \ Video

I'm curious: Was there a specific reason not to use customized loadable CPI fonts via mode command? That's the approach I used years ago.

Re: 6€ MCE2VGA replacement - CGA/EGA/HGC capture with logic analyzer

Posted on 2020-07-17, 10:04

in Marvin \ Video

in Marvin \ Video

@Benedikt the sampling is not jitter free in my opinion. Rendering the full res capture shows definite jitter. You will have to explain the phase offset reconstruction in more detail to me. I personally would have used a median filter on the sampled image with a window size of roundup(samples/pixel …

Re: 6€ MCE2VGA replacement - CGA/EGA/HGC capture with logic analyzer

Posted on 2020-07-17, 09:28

in Marvin \ Video

in Marvin \ Video

Has anyone had the chance to determine whether the 24MHz sampling process itself is jitter free? If it's not, there is no clean solution. But if it is, the secret lies in the phase offset between the sample clock and the original pixel clock, which, as I mentioned before, can be determined via cross …

Re: Best CGA & Hercules games

Posted on 2020-07-14, 11:43

in Marvin \ Software

in Marvin \ Software

There's still the option to write a new BGI driver or set of BGI drivers that impersonates the popular EGAVGA.BGI. That would allow us to run BGI-based EGA or VGA software – predominantly shareware games – on pretty much everything. The approach would be particularly interesting for the various …

Re: Say "Hi!" to the Renovation SSI-2001!

Posted on 2020-07-09, 19:44

in Marvin \ Sound

in Marvin \ Sound

I know. A more sophisticated driver could try to e.g. play chords with a single voice by picking a rectangle wave with a pulse width that yields the desired harmonics. One could also use two cards in parallel. Maybe even different ones like an SSI-2001 and a Tandy PSG card.

Re: CGA/EGA capture with 6€ logic analyser

Posted on 2020-07-09, 19:00

in Marvin \ Video

in Marvin \ Video

I still have some rudimentary C++ and SDL code for the same task since I had virtually the same project idea in 2018 but then abandoned it before it got anywhere. I should really dig that up sometime.

Re: CGA/EGA capture with 6€ logic analyser

Posted on 2020-07-09, 14:59

in Marvin \ Video

in Marvin \ Video

A Sigrok protocol decoder would certainly be possible, but I strongly doubt that it would be usable for anything but still frames. The Python code it probably not even remotely fast enough. You could speed up you own code, though, by reading blocks of data from stdin and iterating over it. Byte-wise …

Re: Say "Hi!" to the Renovation SSI-2001!

Posted on 2020-07-09, 14:53

in Marvin \ Sound

in Marvin \ Sound

Yeah. A fitting DA15 socket would definitely be advisable. By the way: Thanks for the video with the comparison of the SwinSID, ARMSID and 6581 and the short programming example! ( https://youtu.be/CofVqoxVomE ) As matze79 mentioned in a comment, the pitch of the SwinSID is off because it uses its …

Re: Need help with Philips SAA1099 sound chip.

Posted on 2020-07-03, 19:52

in Marvin \ Sound

in Marvin \ Sound

I could never figure it out how, but I think Bit 5 can be used to supply a custom envelope shape to the generator. If I read the datasheet correctly, you cannot supply a custom envelope shape, but control how quickly the envelope generator advances through the envelope shape. You'd basically clock …

Re: Say "Hi!" to the Renovation SSI-2001!

Posted on 2020-07-03, 19:32

in Marvin \ Sound

in Marvin \ Sound

That's a really pretty bracket! But how well does the card fit in the slot with that type of DA15 socket and the bracket on? Does it fit normally or do you have to wiggle around a lot?

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