On Thursday, September 6, 2018 at 5:31 PM, Bob Supnik wrote: > It's not a quirk, it's a design feature. > > The PDP11 simulator didn't start out as a generalized, all-singing, > all-dancing > emulation of all possible PDP11 models; it started as a J11 and PDP-11/73 > simulator - one processor type, one system, Qbus only. In the same way, the > VAX didn't start out as a generalized emulation of all possible VAX models; it > started as a CVAX and MV3900 simulator - one processor type, one system, > Qbus only. These simulator targets were chosen because I managed both chip > projects and had all the design documents, including microcode, for chips and > systems. > > Both the PDP11 and the VAX got extended for entirely legitimate reasons > - to run a broader range of software. Getting to early versions of Unix meant > supporting the PDP-11/45. Getting to early versions of VMS and BSD meant > supporting the VAX-11/780. In both cases, the peculiarities of the Unibus > versus the Qbus were not considered. The Unibus was treated as an 18b > version of the Qbus. > > As the simulators have been generalized, detailed divergences from how the > hardware worked - particularly model by model variances - have surfaced > repeatedly, and the simulators have been refactored accordingly. For example, > the discovery that the VAXstation code in Ultrix violated the SRM but > nonetheless worked on a MicroVAX II required major surgery on the handling > of unaligned references. Unibus DMA to the IO page is just another example of > model-specific differences that must now be accommodated in order to run > more code. > > Except for models that have been written with complete design > documentation in hand, simulation of a model always has limits to its > fidelity. > Within the PDP11 family, I'll vouch for the J11. Many of the other models are > just sketches (think 11/60), really. Within the VAX family, I'll vouch for the > CVAX/MV3900 and the 11/780. The others are adaptations from one of those > two bases and may be incomplete or incorrect on details. > > Mark has a good understanding of what needs to be done. In theory, the same > modifications need to be retrofitted to the 11/780 and other Unibus VAX > models, as well as to the KS10, although I don't think they have the internal > register shielding problem that the PDP-11 does.
I'm going to leave that as a theory until a use case actually comes along that wants to do this. None of the few examples of devices that want to do NPR to the I/O Page have related software that runs on any VAX OS. When Tim added the initial NPR I/O page support some 5 years ago, that was limited to the PDP11. A refinement example has come along now, but not a peep on the VAX Unibus side of things. I looked at it and it's not just cut and paste, so without a test case I'd rather implement something that actually works rather than might work. - Mark _______________________________________________ Simh mailing list Simh@trailing-edge.com http://mailman.trailing-edge.com/mailman/listinfo/simh