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RE: Execute-in-Place (XIP) from flash?



That is correct but I can't really see the point. Linux will page
in pieces of the executable form flash to the page cache when a
program is executed. If memory is low the program will be paged
back to flash (except for dirty pages of cours). 

So for me there is two questions:

1. How are you going to tell the kernel that it should use XIP?
2. How will you benefit from it? One answer may be that you want
to avoid pageing in and out for performance reasons.

Even if you manage to do true XIP you will still have all the
writable segments of the applications in RAM.

Can you tell us more why you have so little RAM left but so
much flash? 

/Mikael

-----Original Message-----
From: owner-dev-etrax@xxxxxxx.com">mailto:owner-dev-etrax@xxxxxxx.com] On
Behalf Of Fettahlioglu, Mahmut
Sent: Tuesday, September 21, 2004 3:56 AM
To: Jonas Holmberg
Cc: dev-etrax
Subject: RE: Execute-in-Place (XIP) from flash?


Thanks for the info Jonas.

It looks like the only chip available for this project will be the
internal
flash. It will be alright to use it entirely as read-only. As long as I
guarantee XIP processes do not run during FTP flash reprogramming it
should
work fine then?

Thanks,
Mahmut

> -----Original Message-----
> From: Jonas Holmberg [mailto:jonas.holmberg@xxxxxxx.com]
> Sent: Monday, 20 September 2004 5:38 PM
> To: Fettahlioglu, Mahmut
> Cc: ETRAX development list
> Subject: Re: Execute-in-Place (XIP) from flash?
> 
> On Mon, Sep 20, 2004 at 01:56:45PM +1000, Fettahlioglu, Mahmut wrote:
> > Hi all,
> >
> > I was wondering if there is a way I can use execute-in-place with
> MCM4+16
> > chips to save runtime memory. The options seem to be:
> >
> > - Use the internal flash "/etc" partition. This would involve
formatting
> the
> > JFFS2 partition with something else e.g. FAT as JFFS2 uses
compression.
> >
> > - Use an external USB flash ad run the software from there
> >
> > Do you think there are some limitations that prevent one or both of
> these
> > options? And if it can be done, do I need to change something in the
> kernel
> > for this?
> >
> > Any feedback welcome. Thanks to all,
> 
> To be able to write to flash and do XIP at the same time you need more
> than one chip. You must never write or erase the chip you execute code
> from.
> 
> /Jonas