Re: NetBSD in SIMH vax with 512 MB RAM

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

> [...] - I noticed that when SIMH is configured with 512MB of memory,
> the calculated size of the system page table ends up being a bit
> larger than the 2^21 entries needed to map all of system space.

That's odd.  Maybe it's reserving enough space for _two_ copies of
physical memory or something?

I also think that's a theoretical bug; EL-00032-00-decStd32_Jan90 says

   |  Thus, there could be as many as 2**21 pages in the system region.   In
   |  order  to express the values 0 through 2**21 (200000 (hex)) inclusive,
   |  the length field in the SLR is 22 bits.  SLR values not in  the  range
   |  of  0  to  200000  (hex)  inclusive  are reserved values and result in
   |  UNDEFINED operation.

I'd be surprised if an implementation didn't simply use a 22-bit
register, capable of representing 0 through 3fffff, but it looks to me
as though implementors have the latitude to do otherwise.  At least for
models for which that's the applicable VARM.

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