My Memory map ... how do i pick the virtual address (Aside fr om i mmr and sdram)

[James Don]

I found my answers ...

I did find this in a post from a guy called Dan Malek (m-vista I think):

"As I have explained before, the IMMR and possibly a few other
board control registers must have physical addresses above
0x80000000. This is because the early kernel initialization
will map these 1:1 virtual to physical. They are needed before
the kernel VM allocator has been initialized. If they are
below this address, they clash with the user virtual space,
so depending upon the loading of programs and libraries, you
left a big virtual hole into kernel managed hardware."

And I found this great post on how to pick your map ...
http://lists.linuxppc.org/linuxppc-embedded/200010/msg00153.html

Jim

-----Original Message-----
From: Rod Boyce [mailto:rod_boyce at stratexnet.com]
Sent: Tuesday, January 21, 2003 8:05 PM
To: 'jgdon'
Cc: 'James Don'; linuxppc-embedded at lists.linuxppc.org
Subject: RE: My Memory map ... how do i pick the virtual address (Aside fr
om i mmr and sdram)

I can tell you now the mapping between physical and virtual not as important
as you make out.  I have Linux running on a board I described to you and
there is no RAM mapped at 0xc0000000.  I suggest you read your chip manual
more carefully.  In my 860 PowerQUICC Users manual chapters 13,14 and 16.

I also remember reading somewhere at IO should be mapped above 0x80000000
but I have not been able to find where I read it in the last two years so
that could be another urban myth that need the cold light of day on it.

Regards,
Rod Boyce

 -----Original Message-----
From: 	jgdon [mailto:jgdon at gomba.ca]
Sent:	Wednesday, 22 January 2003 2:56 p.m.
To:	Rod Boyce
Cc:	'James Don'; linuxppc-embedded at lists.linuxppc.org
Subject:	RE: My Memory map ... how do i pick the virtual address
(Aside fr om i mmr and sdram)

Hi,
I think the the mapping of virtual to physical address may be important
... i believe ram should be at 0xc0000000 for a number of reasons ...
there is lots of posts regarding this ...

What I am worried about is "rules of thumb" for example i have an ASIC on
cs4 ... at BR4 0x08000000 ... I would like to map it to 0x08000000 in the
MMU ... i would just like to be sure this is an ok address to check ... or
if there is some generally accepts address range for "non memeory" device
stuff ... I assume 'no' ... but i also assume the immr address and sdram
address didn't matter at one time ...

Jim

On Wed, 22 Jan 2003, Rod Boyce wrote:

>
> I think you have the wrong end of the stick.  Our boards have 32MB of RAM
> located at 0.  We have placed IMMR at 0xfa200000.  The address of
0xc0000000
> is a virtual address it does not have to have any relation to a physical
> address this is done by the memory manager.  The only constant is that the
> boot flash MUST be connected to chip select 0.  Everything else is mostly
> software configurable.
>
> Regards,
> Rod Boyce.
>
>  -----Original Message-----
> From: 	James Don [mailto:JDon at spacebridge.com]
> Sent:	Wednesday, 22 January 2003 12:58 p.m.
> To:	linuxppc-embedded at lists.linuxppc.org
> Subject:	My Memory map ... how do i pick the virtual address (Aside
> from i mmr and sdram)
>
>
> Hi,
>
> I am just looking at adding my other mem mapped devices to Linux for my
> custom MPC860 board ...
>
> I know RAM has to be at 0xc0000000 and immr at 0xff000000 ... is there any
> rule of thumb for anything else?
>
> Jim
>
>
>

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