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Re: Setting the physical RAM map

To: David VomLehn <dvomlehn@cisco.com>
Subject: Re: Setting the physical RAM map
From: Geert Uytterhoeven <geert@linux-m68k.org>
Date: Mon, 30 Nov 2009 20:25:51 +0100
Cc: Adam Nielsen <a.nielsen@shikadi.net>, linux-mips@linux-mips.org
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On Mon, Nov 30, 2009 at 20:00, David VomLehn <dvomlehn@cisco.com> wrote:
> On Sun, Nov 29, 2009 at 12:38:55AM +1000, Adam Nielsen wrote:
>> I'm attempting to port the Linux kernel to an NCD HMX, an R4600-based 
>> X-Terminal.
> ...
>> It gets as far as printing the physical RAM map and then crashes, but I'm
>> not sure why:
>>
>>   Determined physical RAM map:
>>    memory: 00800000 @ 40250000 (usable)
>>    memory: 00040000 @ 9fc00000 (ROM data)
>>   Wasting 8407552 bytes for tracking 262736 unused pages
>
> These are kernel messages, so you are getting into the kernel, but this
> looks odd to me.  The MIPS processor needs memory mapped in the first
> 512 MiB to execute. This first 512 MiB will be mapped as cached memory
> at virtual address 0x80000000 (known as kseg0) and as uncached memory at
> virtual address 0x0a0000000 (known as kseg1). Perhaps you system is like
> mine, where I have memory above 512 MiB aliased into the first 512 MiB
> of physical space.
>
> The second odd thing is the ROM data physical address. This is a good virtual
> address but as a physical address it is not accessible by the MIPS processor
> without mapping to with a TLB entry.

9fc00000 is kseg0. kseg0 has 512 MiB, so that's not only 0x8???????, but also
0x9???????.

Gr{oetje,eeting}s,

                                                Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                                            -- Linus Torvalds

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