[Info-vax] Baremetal emulators, was: Re: Alpha emulator for OSX

[Simon Clubley]

On 2016-02-08, lists at openmailbox.org <lists at openmailbox.org> wrote:
> On Mon, 8 Feb 2016 04:10:38 -0800 (PST)
> johnwallace4--- via Info-vax <info-vax at rbnsn.com> wrote:
>> 
>> You mention bare metal. Arie says "vtAlpha runs on X86 without the
>> need for an extra OS like Windows or Linux." He doesn't say "bare
>> metal" here, but the term is used on their website.
>> 
>> Unless something has changed since the last significant discussions
>> I remember on this topic (several years ago), vtAlpha runs on top of
>> a cut down Linux (it'd be unrealistic to expect it to run on random
>> x86 systems *without* an underlying OS, or at least a HYPErvisor).
>> 
>> So it may not fit everyone's definition of "bare metal". Others may be 
>> perfectly happy with a setup like that. Take your pick.
>
> Thanks, that's a good point. I probably misunderstood what was said in the
> post although the fact you say "bare metal" is mentioned on the website
> does muddy the waters. From the end-user point of view there isn't much
> practical difference but from a technology point of view there is certainly
> quite a distinction and it would be nice to clarify how it works.
>

There is potentially a major difference from the end-user viewpoint if you
are trying to run real-time applications.

Let's keep this simple for the benefit of those (_not_ you!) who try to
confuse the issues here.

Does the part of the Alpha emulator which is concerned with doing the
emulation directly talk to the device registers in the hardware on the
host system ?

If yes, then it's bare metal. If no, and it talks to some intermediate
OS's syscalls layer instead of the hardware then it's not bare metal.
BTW, it doesn't matter if that OS layer is bundled with the emulator or
not; it's still an intermediate OS layer either way.

However, if the underlying OS has real-time guarantees (say it's a RTOS
for example) then you _might_ still be able to meet the real-time
requirements of the application.

Don't forget that real-time doesn't mean fast; it means a _guaranteed_
bounded response time. That's something which a surprising number of
people don't seem to understand.

Simon.

-- 
Simon Clubley, clubley at remove_me.eisner.decus.org-Earth.UFP
Microsoft: Bringing you 1980s technology to a 21st century world