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popularity : 53% |
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alltime top: #16816 |
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added on the 2025-10-05 16:22:13 by bodo^rab  |
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popularity helper
comments
Obscure platform, research, skilled technique. This demo as all of it. I bow down to you, this is the new standard in the PET world!
rulez added on the 2025-10-05 17:22:07 by Elder0010 
-It's an introduction to a new graphics modes:
Interlace: 80x50 Chars
(Hires)-GFX
Mode8 (8 shades of green)
-First PET-Disk-Fastloader
-Very large sample (640KB)
Interlace: 80x50 Chars
(Hires)-GFX
Mode8 (8 shades of green)
-First PET-Disk-Fastloader
-Very large sample (640KB)
geil
Interesting graphics mode and other technical advancements.
Amazing! Absolutely high-end. This platform is "finished" now ;-) Definitely needs a write-up/seminar of how all of this is possible.
What is this sorcery‽
Wow!
8 shades? fullscreen bitmap? what the... ?
Impressive
Amazing!!
Crazy!
You got me with the first 3rd of the demo where I was like "guess this is pretty good for PET" and then WOW!
You are officially insane
I have some questions, such as:
What?
and
How?
What?
and
How?
I would have preferred a balance tipped towards effects, rather than playing music. But regardless of personal preference, this is an awesome feat!
Amazing!
a little heavy on the green side of things, but otherwise kinda cool ;)
but who am i kidding. i know a lot of research and work into this and the result is nothing short of the best PET demo ever made (period).
and while i know why you changed the style of music so much (yes, to SHOW OFF!) i would like to add digis are cool and all that but could you just use samples that are actually less noisy and more pleasent? kthxbye.
but who am i kidding. i know a lot of research and work into this and the result is nothing short of the best PET demo ever made (period).
and while i know why you changed the style of music so much (yes, to SHOW OFF!) i would like to add digis are cool and all that but could you just use samples that are actually less noisy and more pleasent? kthxbye.
Goiler Scheiß!
Geil! The tech details are worth sharing or a writeup. BG Rabenauge!
rulez
Crazy good for the platform! Kudos!
We had to rush things a lot, so... watch out for the final version! =)
Here's a short breakdown of how the bitmap/rasters+samples stuff works:
CRTC allows character lines to be just one raster line high. Problems to solve then are best-fitting bitmap byte patterns to whatever is available in the first line of the fixed font's chars, a bit of strategic CRTC register massage to get more than 128 "char"lines per videoframe, and setting an arbitrary display pointer each raster line.
The latter two problems became a lot easier once we came across "The Amstrad CPC CRTC Compendium", so we could build on decades of prior research done by the CPC scene.
(The Commodore/MOS CRTC variant also seems to relate very closely to the easier not-so-quirky Motorola variant rather than the not-so-easy 2nd-source variants also found in CPCs.)
The samples are driven using the VIA chip's shift register, which allows for clocking out "something like" 7.8 KHz 4-bit PCM samples at 125 KHz (8 µs per bit) in the form of pulse-trains of 16 pulses per two rasterlines, with one shift register update per rasterline.
(This is closer to pulse-density modulation than pulse-width modulation, so more-or-less harmonic quantisation noise is spread a bit around the spectrum rather than accumulating at some tinnitus carrier frequency.)
Both CRTC video registers and shift-register audio updates are interwoven in a rasterline-pair-based loop, so the cost of context-switching via interrupt handlers etc. is avoided.
(Double-rasterline not only because of the 7.8 KHz samples, but also because having some ordered dithering on the single shade of green seemed like a good idea.)
Here's a short breakdown of how the bitmap/rasters+samples stuff works:
CRTC allows character lines to be just one raster line high. Problems to solve then are best-fitting bitmap byte patterns to whatever is available in the first line of the fixed font's chars, a bit of strategic CRTC register massage to get more than 128 "char"lines per videoframe, and setting an arbitrary display pointer each raster line.
The latter two problems became a lot easier once we came across "The Amstrad CPC CRTC Compendium", so we could build on decades of prior research done by the CPC scene.
(The Commodore/MOS CRTC variant also seems to relate very closely to the easier not-so-quirky Motorola variant rather than the not-so-easy 2nd-source variants also found in CPCs.)
The samples are driven using the VIA chip's shift register, which allows for clocking out "something like" 7.8 KHz 4-bit PCM samples at 125 KHz (8 µs per bit) in the form of pulse-trains of 16 pulses per two rasterlines, with one shift register update per rasterline.
(This is closer to pulse-density modulation than pulse-width modulation, so more-or-less harmonic quantisation noise is spread a bit around the spectrum rather than accumulating at some tinnitus carrier frequency.)
Both CRTC video registers and shift-register audio updates are interwoven in a rasterline-pair-based loop, so the cost of context-switching via interrupt handlers etc. is avoided.
(Double-rasterline not only because of the 7.8 KHz samples, but also because having some ordered dithering on the single shade of green seemed like a good idea.)
A demo in the truest sense of the word, human ingenuity and huge amounts of actual hardware thrown at the proof, operating in zones where hardly any comfort exists, unlocking feature after feature along the way in the oldest school possible.
Jesus Christ, I thought your demo for Deadline 2022 was sheer wizardry, but this, this! Wicked to hear one of my favourite dalezy joints smashed through this thing at the end too.
So fucking cool, diese grüne Jugend 💚
great
This looks fantastic! I havent tried it yet, my original PET is an 8k 1978 2001 model, so I do not think this will work because I think this uses the 6545 CRTC chip on the later PET 4032 model. Its is worth mentioning this here.
Advanced gfx is also possible on the old 2001, but more of a challenge, it has slow video ram that causes snow if you access the screen at the wrong time, and you do not have the flexible 6545, just TTL. For a long time I wanted to make such a demo, chasing the beam and switching chars for 320x200 plotting, but now it has been done!
Advanced gfx is also possible on the old 2001, but more of a challenge, it has slow video ram that causes snow if you access the screen at the wrong time, and you do not have the flexible 6545, just TTL. For a long time I wanted to make such a demo, chasing the beam and switching chars for 320x200 plotting, but now it has been done!
Finally watched it. Congrats on this achievement!
Meant to comment earlier on this!
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instead, click here !