Re: For the AdaOS folks

["Warren W. Gay VE3WWG" <ve3wwg@NoSPAM.cogeco.ca>]

Marven Lee wrote:
> Warren W. Gay VE3WWG wrote:
>>Dmitry A. Kazakov wrote:
>>>Warren W. Gay VE3WWG wrote:
>>>
>>>>The problem then is that the drivers add to the code in "real-mode",
>>>>which is one thing that the mk tries to avoid (for additional safety
>>>>and modularity).
>>>
>>>I am still not sure what you mean here. If you mean modular kernel
>>>design and more fine-grained system of modes than all-or-nothing,
>>>then yes, sure. There is no reason, why a driver should not be
>>>treated as an application.
>>
>>That's right. Just remember that the purpose of the mk is to keep the
>>"priviledged-mode" code to a bare minimum (hence the "micro").
> 
> Some microkernels and single address space operating systems
> implement cross-domain call mechanisms that enables a thread
> to cross from one protection domain into another in a similar
> way as a segmented system performs far calls or interrupts
> and traps can transfer from user-mode to kernel-mode.
> 
> In Mach it's called "migrating threads".

Yes, I've seen references to this in the Mach
literature.

> The Spring Nucleus (and Solaris) has cross-domain calls through "Doors".
> In the Pebble Operating System it's called "Portal Traversal"
> Mungi has "Protection Domain eXtensions".
> I think the Grasshopper kernel has something similar.
> Maybe LPC in Windows is a form of cross-domain call, I'm not sure.
> 
> You can end up with a microkernel that only handles cross-domain
> calls.  Everything else, including what you normally think
> a microkernel should at least include,

I'm glad you said "normally" here. ;-)

> such as memory management,
> scheduling and IPC can be implemented outside of the microkernel.
> 
> Marv 

Exokernel?

   http://www.pdos.lcs.mit.edu/exo.html

I've never been too keen on the single address space systems. But
I did like the way the ring mechanism worked in PrimOS (not a mk),
which was probably borrowed from Multics. I liked the way the
links were "snapped" and the way that you could call into different
levels of protection.

Cross domain threads is an interesting idea though. I'll check it
out.
-- 
Warren W. Gay VE3WWG
http://home.cogeco.ca/~ve3wwg