Answering my own question as a way to spur up discussion two years later...
Based on this question and its accepted answer here: What are the Ultra-Highres registers in ECS and AGA for? , namely, the fact that AGA, and perhaps ECS already, has a DUAL/UHRES mode that is meant to drive an external CLUT/DAC connected to Vram to generate a second, high-resolution, display independently of the one generated by Denise/Lisa, I'm now convinced that indeed the Ranger chipset may actually have been implemented as either ECS or AGA.
In fact, these are reportedly the feature that Ranger had (1):
- The chip RAM maximum being 2MB rather than 512K.
- The possibility for a 1024x1024 non-interlaced display.
- The use of VRam to attain the above resolution.
ECS has:
- 2MB for chip RAM maximum.
- The 35ns SuperHires mode, which prove that it's fast enough to go above the ~ 700 pixel horizontal resolution that OCS can do (with overscan).
- a "DUAL" bit in register BEAMCOM0 (introduced in ECS) to enable a mode that is described as a "Special ultra resolution mode" (briefly mentioned in the RKM: Hardware book, 3rd edition, but never described in detail).
(Note that Alice in AGA isn't much more than ECS's Super Agnus with the ability to run a 2-cycles Fast Page mode access on a 32bit wide bus for bitplane and sprite data only and very little more than that).
IMHO it may very well be that after Jay Miner left Commodore in 1987/88 when Los Gatos closed, Commodore did indeed use his design for "Ranger" and implemented a version of the design already in ECS with Super Agnus, and then later in Alice (with the version in ECS perhaps being buggy or incomplete, and the version in AGA being instead stable enough to being documented in the official list of the chipset registers).
... except then they never went on releasing a system that actually used the VRam mode (due to requiring RTG in software? due to the usual lack of vision?), least implement a new custom chip to drive the VRam (*).
Thoughts?
Addendum: the internal memo describing the AAA chipset says:
AAA is designed to be largely register compatible with the ECS chip set. Most of the RGA registers from ECS are supported. The ECS “Ultra hires” registers have been eliminated, as they were never supported in actual practice. Some other display-generation details of ECS are no longer required or supported in AAA.
So it looks like this feature has ben around since ECS.
(*): could this VRam driver/CLUT/DAC "external circuitry" implementation actually be the Kelly chip originally developed for AGA?
could this VRam driver/CLUT/DAC "external circuitry" implementation actually be the Kelly chip originally developed for AGA?
could it be that the 0xC000000 "slow-fast RAM" memory is known as the "Ranger RAM" because this is where the VRam was supposed to be mapped in the memory map. VRam still needs to be accessible as normal RAM too, after all.