Re: [openrisc] Multiprocessing and virtual memory

[mbtirado@mundivia.com]

In OR1200 page table can not be duplicated for every CID because CID 
bits are hardwired to zero! Is possible to run an operative system with 
virtual memory on OR1200 CPU?

----- Original Message ----- 
From: Marko Mlinar <markom@o... > 
To: openrisc@o...  
Date: Thu, 17 Oct 2002 14:29:32 +0200 
Subject: Re: [openrisc] Multiprocessing and virtual memory 

> 
> 
> On Thursday 17 October 2002 13:37, mbtirado@m...  wrote: 
> > Hello. 
> > I've read your reply about CID bits. Thank you very much for 
> answering 
> > so quickly. 
> > Your answer has led me to a new question: how does the 
> operative 
> > system the management of the virtual memory? 
> > Let's consider two different processes running concurrently on 
> the same 
> > OR1200 CPU. Could these processes have access to the entire 
> virtual 
> > memory space? If so, since OR1200 doesn't use CID bits the two 
> > processes may use repeated virtual addresses that obviously 
> wouldn't 
> > represent the same physical address, as they are two different 
> > processes with two different physical memory spaces. 
> > I can think about two possible solutions to this problem: 
> > 1. The Page Table would need to be replaced with every context 
> > change. This solution would have an enormous penalization, so 
> I don't 
> > think it would be suitable. 
> > 2. The two processes wouldn't have access to the entire 
> virtual memory 
> > space, but the operative system would distribute portions of 
> virtual 
> > memory that processes could use. 
> > What I need to know is: which of these solutions (or a 
> different one 
> > that I haven't thought about) would an OR1000 compatible 
> operative 
> > system (as for example your porting of uCLinux) use? 
> > Thank you for your help. 
> > Marķa Bolado. 
> 
> If I am not wrong, CID is part of virtual address (look in 
> documentation), 
> this should answer most of your questions. 
> The hardware page table would not need to be replaced, since it can 
> be 
> duplicated for every CID. 
> uClinux is Linux without MMU. 
> 
> Marko 
> 
--
To unsubscribe from openrisc mailing list please visit http://www.opencores.org/mailinglists.shtml