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Re: Kernel located in KSEG2 or KSEG3.

To: Ralf Baechle <ralf@linux-mips.org>
Subject: Re: Kernel located in KSEG2 or KSEG3.
From: moreau francis <francis_moreau2000@yahoo.fr>
Date: Thu, 16 Dec 2004 16:05:36 +0100 (CET)
Cc: linux-mips@linux-mips.org
In-reply-to: <20041215133851.GD27935@linux-mips.org>
Original-recipient: rfc822;linux-mips@linux-mips.org
Sender: linux-mips-bounce@linux-mips.org
> It's not.  The 4kc processor when running with the
> BEV bit in the status
> register cleared will try to find it's exception
> vectors at address
> KSEG0, so there would have to be *some* code mapped
> there.  With BEV=1
> exception vectors would be located in the firmware
> as pointed out by
> Steve in his answer.  Firmware means something like
> flashmemory and running
> uncached, so will be prohibitivly slow.  I just
> can't believe a system to
> be that missdesigned!

Well actually I have memories that can be accessed by
KSEG0, but they are very limited:

start        size      type
----------------------------
0x00000000 - 128Ko    - RAM
0x01000000 - 128Ko    - FLASH
0x1fc00000 - 128Ko    - ROM

Therefore I could use this internal RAM to store
exception vectors.

My fears are on running kernel in KSEG2.

I'm thinking of trying this configuration:

I'm going to use 2 TLB entries to map definetively
kernel in KSEG1:
    * 1 entry to map kernel code in FLASH (16Mo), 
    * 1 entry to map kernel data in SDRAM (8Mo).

space    virtual-add    physical-add    size
----------------------------------------------
Code     0xC0000000     0x30000000      16Mo
Data     0xC1000000     0x20000000       8Mo

I will set PAGE_OFFSET to 0xA1000000, therefore all
physicall address convertion will result in SDRAM.
Hopefully, this macro is only used to make translation
between physical and virtual spaces. I grep it and it
seems to be the case.

Do you think that I can dig at this way ?

Thanks,

   Francis



        

        
                
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