Cirrus Logic based Z2/Z3 RTG board similarities

[Toni Wilen]

While developing board emulation, I noticed most Cirrus Logic based boards have nearly identical Zorro logic. (Excluding Picasso IV which is special). I originally thought they are different and only planned to emulate PicassoII/II+.

Picasso II/II+, Piccolo, Piccolo SD and Spectrum 24/28 all have 2 virtual autoconfig boards, one for IO ports and another for VRAM.

Piccolo/Piccolo SD and Spectrum have passthrough/interrupt enable IO port in exact same address (base addr + 0x8000) and uses exact same bits. (This port is not inside Cirrus Logic chip). They also have swapped R and B color components in hardware. Main difference seems to be autoconfig product/manufacturer id!

Did board developers base their own design on some existing design/product or did they share or copy designs?

EDIT: Please fix typo in title..

[alexh]

You could ask Tobias Seiler aka Mastatabs over at amiga.org as he was a Picasso developer at VillageTronic.

http://www.sophisticated-development.de/

Olaf Barthel was also a good source of info.

[alexh]

This defunct website was also a good source of info

http://web.archive.org/web/200410091...fx/boards.html

It hints that several of the boards were based around the never released "Graffity" by Atéo Concepts (not Graffiti by Individual Computing). It's software was the precursor to Picasso96

[prowler]

Originally Posted by Toni Wilen

EDIT: Please fix typo in title..

Done.

[SpeedGeek]

I simple explanation for the Zorro2 graphics boards configuring as an I/O device and VRAM is the Zorro2 memory map which separates Zorro2 I/O and memory functions. (This is not the case for Zorro3 boards but my GVP Spectrum still configs one device in Zorro2 I/O space even in Zorro3 mode).

As far as the other similarities it may have been done for software compatibility or just because the boards use the same graphics chip. The PicassoII being one of the first real RTG boards was in a good position to set some standards.