PED81C: A video system for AGA Amigas that provides pseudo-native chunky screens | Hacker News Reader

PED81C: A video system for AGA Amigas that provides pseudo-native chunky screens

retream.itch.io

43 pointsdoener12 comments

Any way to see what it's doing without downloading the lha? Hard to look at archives from my phone.

This [0] thread on EAB has a bit of an explanation, though I don't really understand it.

[0] https://eab.abime.net/showthread.php?t=109962

1280 SHRES mode and exploiting the fact analog CRT TV wont be able to display this and interpolate down to 160 pixels worth of ~80 colors. The key seems to be bad TV and sitting far away :) Only one bitplane is filled with actual color data, 1280 / 8 = 160, all other bitmaps are prefilled with special patterns, system bus is heavily saturated leaving very little for CPU.

This gave me different idea instead of smearing colors on TV. 2x RP2040 pico. One soldered on top of Hybrid/DAC where it accumulates digital data 8 clocks at a time and automagically translates planar to chunky, second RP2040 playing a role of DAC. Sprites not supported for obvious reason, need all the pixels pushed out to reconstruct flat chunky data. 2x pico because one doesnt have enough pins to fit everything, and fpga/cpld uneconomical in the face of $1 RP2040s.

OCS/ECS Hires 640x @16 colors would produce 320x200@256 with zero performance penalty out of A1000/500.

This is ~how Commodore A2024 monitor worked internally, except 23pin Video Connector had only 4 digital data bits resulting in stupid refresh rate. ~1000x1000 at 10Hz https://bigbookofamigahardware.com/bboah/product.aspx?id=863

Afaik Commodore Akiko chip was so braindead it took chunky data in and translated that into multiple planar writes to ram killing any potential speed advantage.

I vaguely remember a device back in the day that buffered a 4 bitplane 640 pixel scanline to output a 320 pixel 256 colour mode.

Seems entirely doable on a rp2040. The arm cores have so much power that there's hardy any work that you'd use the Amiga for though.

> 4 bitplane 640 pixel scanline to output a 320 pixel 256 colour mode

yeah, you are right with 320. Means no need for any soldering inside Amiga, can just plug into Video Connector like A2024 monitor, and one RP2040 is enough.

> I vaguely remember a device back in the day

me too! I think it was dedicated to Video processing? or maybe bundled with a scanner? and most likely required you to massage bits on computer side.

Edit: found it! https://bigbookofamigahardware.com/bboah/product.aspx?id=481 I think this https://bigbookofamigahardware.com/bboah/product.aspx?id=503 also worked in similar way.

There's also https://bigbookofamigahardware.com/bboah/product.aspx?id=498

Yes! I definitely also saw this one long time ago. Most likely my "independent" idea from post above was my brain just re creating this very product from memory :] GAL, few TTLs, SRAM? and a DAC, easy and cheap to manufacture and obvious once you saw IMS G171 being released in 1986 (year before vga). Another missed opportunity by Commodore, A500 should have had a socket for INMOS G171 right on the motherboard in 1987, maybe even a flap on top of the case for easy upgrade access.

Today $10 RP2040 pico board and a resistor ladder can implement it easily.

You are refering to the DCTV? Was also used as a digitizer. Still got mine.

Nostalgia does weird things.

Yes, DCTV! Funnily enough it turns out I followed this post all the way back in 2017: https://retrocomputing.stackexchange.com/questions/2201/how-... and just got email because someone updated that thread yesterday :)

> Afaik Commodore Akiko chip was so braindead it took chunky data in and translated that into multiple planar writes to ram killing any potential speed advantage.

Even worse than that it didn't write them to ram - you had to read the planar data out of the registers and write them to ram yourself

What is a 'video system'?

This is a really clever hack!

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