Cirrus Logic based Z2/Z3 RTG board similarities
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..