Re: NetBSD/vax vm for github testing

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

Den 2025-01-11 kl. 15:29, skrev John Klos:
> > I wrote multiprocessor support for NetBSD/vax many years ago; but not 
> > many vax machines can
> > have multiple CPUs. It did work on VAX8250, which was just over one 
> > VUPS (which is extremely
> > slow today). Also, emulating multiprocessor support in general using 
> > a multiprocessor
> > machine is extremely difficult, since you need to synchronise the 
> > CPUs so that they emulate
> > at exactly the same speed. -- Ragge
>
> Just curious: why would multiple CPUs need to emulate at exactly the 
> same speed? I've read about multiprocessor VAXen running different 
> CPUs, and I've run different CPUs on other architectures (Celery and 
> Pentium II with i386, SPARC and HyperSPARC on, well, sparc).
>
> Were the people running different CPUs in a VAX doing something 
> different?
>
> BTW - someone modified SIMH to run multiple CPUs, but only supported 
> OpenVMS. The author had no interest in NetBSD.
I was referring to a simulator that mimics the hardware, not writing a 
new design of some invented hardware layout (as VAX MP is).
There are very few VAXen with multiple CPUs, and those that existed had 
very close cooperation between the CPUs (the 6000 series for example).

-- Ragge