Re: [oc] Re: Merlin Hybrid System

["Jim Dempsey" <dempsey@northnet.net>]

----- Original Message ----- 
From: "Andreas Bombe" <bombe@informatik.tu-muenchen.de>
To: <cores@opencores.org>
Sent: Thursday, December 13, 2001 7:29 PM
Subject: [oc] Re: Merlin Hybrid System


> 
> These FPUs were however synchronized explicitly whenever the operating
> system wanted to switch context,
The interrupt processing service did not have to save and restore the FPU
if it did not muck with the FPU. It could let it continue on it's own.
Granted, it is a far cry of a difference between letting th FPU run and
doing a thread switch.

> 
> What happens at an interrupt is that the exception frame with the
> address of the interrupted instruction gets pushed on the stack.

Yes, so?

> Registers stay (unless you have different register banks, which the x86
> has not).  The interrupt handler pushes all registers on stack.  If the
> user mode would still run, saved values (address, register contents)
> would not match changing reality.
> 

Rember you have virtualized the x86.
You are free to do some hocus-pokus.

> How would you synchronize that, what would happen when the interrupt
> handler wants to restore user context?  Hunt down the values in memory
> and change them?  Where would you find them?
> 

Rember you have virtualized the x86.
You are free to do some hocus-pokus.

Jim Dempsey


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