Re: Does the KA630 have a TB?

[Johnny Billquist <bqt%softjar.se@localhost>]

On 2023-09-24 22:01, Mouse wrote:
> > > > > > Why not cache entries outside main memory, by the way?
> > > > > [...JIT...]
> > > > [...]
> > > [...] cache (faster-to-access forms of) PTEs for virtual addresses
> > > that map to main memory, but nothing else [...]
> > The first lookup (which is what would go through the TB if an entry
> > exists there) is what always have to happen.  [...] just caching so
> > that you don't have to go via the PTE in case there is a TB hit seems
> > like always a win.  I don't see any gain in just not caching some
> > entries.  Or, hmm.  Ok, so you know that if you hit in TB, it's
> > memory.  So you can skip one compare after the TB lookup in that
> > case.
>
> Hm, true, it is just the one compare.  Well, a load-from-memory and a
> compare, but the load from memory is likely to hit the (real) CPU's
> cache, because the VAX goes to memory frequently.
>
> I hadn't thought it through enough; thank you.

When you have done the translation, if the physical address > 0x2000 
0000, it's the I/O page/area. And then you can work things out after that.

> > > Well, the 1.4T kernel I'm working with definitely uses 4K pages.
> > Change was back in 1998-08-21.  Thanks for just reminding me how old
> > I'm getting. :-)
>
> I know the feeling, I know the feeling.  Just recently I had someone
> tell me I'd been writing C longer than he'd been _alive_.

Heh... Don't even remind of such things.

  Johnny

--
Johnny Billquist                  || "I'm on a bus
                                  ||  on a psychedelic trip
email: bqt%softjar.se@localhost             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol