Re: NetBSD in SIMH vax with 512 MB RAM

[Anders Magnusson <ragge%tethuvudet.se@localhost>]

Den 2023-03-22 kl. 06:08, skrev Kalvis Duckmanton:
> On 20/3/23 14:57, Kalvis Duckmanton wrote:
> > On 18/3/23 06:26, Rhialto wrote:
> >
> > > 4. Perhaps this is the reason why the whole thing doesn't work if you
> > >     have a lot of RAM: if we take the comment "beyond the end of the
> > >     system page table" at face value, then maybe such a large memory
> > >     configuration causes the page tables to grow enough that the 
> > > T_PTELEN
> > >     trap does not occur. Instead there would be some other trap type.
>
> So just further to this - 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.  (The value I saw in the system length register was 0x23eef0 
> (2^21 is 0x200000) - I think in such a case a length violation fault 
> will never be generated.)
SLR contains the length of the kernel virtual space, which do not 
neccessarily correlate with the physical memory size.
Note though that NetBSD maps the physical memory first in system space, 
then virtual memory.

-- R