Reading from physical addresses..

Eric Valette eric.valette at
Fri May 2 19:04:28 UTC 2003

Aaron J. Grier wrote:

> RTEMS is designed for use in embedded environments which may or may not
> have memory protection available, and assumes a flat memory map.  on
> systems with MMU hardware, some minimal memory protection may be
> applied, but there's no virtual memory or per-process memory spaces on
> any RTEMS targets as far as I am aware.
> I run on MMU-less m68k hardware; perhaps someone else here with more
> advanced processor can volunteer more specifics?  ;)

Well just to give a small different perspective, I will put my two 
cents. I think we can say this a little bit differently : RTEMS code 
assume a 1-1 physical/virtual memory mapping and no protection across 
kernel/application space. There are a couple of CPU where MMU is enabled 
with a 1-1 mapping :
	1) IX86 because there is no way to disable caching selectively and you 
cannot turn the cache entirely off for performance reasons but you need 
to disable it for memory mapped via PCI address space for ethernet 
drivers for example,
	2) On some processor you cannot turn the cache on without the MMU

   /  `                   	Eric Valette
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