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List:       bluesmoke-devel
Subject:    Re: Supporting a new memory controller
From:       Joshua Wise <wise () sicortex ! com>
Date:       2006-07-07 20:51:22
Message-ID: Pine.LNX.4.64.0607071558170.26057 () gs107 ! sicortex ! com
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On Fri, 7 Jul 2006, Doug Thompson wrote:
>> We will have two DIMMs, each up to 2-rank (although 4-rank may be supported
>> at our discretion later). So, right there, each DIMM has 2 CSROWs. But, we
>> don't separate the DIMMs out at the top of memroy -- rather, we separate
>> them out by address bit 6. So:
>>
>> [     0MB]+0000000000000000 DIMM0, CS0
>> [     0MB]+0000000000100000 DIMM1, CS0
>> [     0MB]+0000000001000000 DIMM0, CS0
>> [     0MB]+0000000001100000 DIMM1, CS0
>> [...]
>> [memory/2]-0000000001000000 DIMM0, CS0
>> [memory/2]-0000000000100000 DIMM1, CS0
>> [memory/2]+0000000000000000 DIMM0, CS1
>> [memory/2]+0000000000100000 DIMM1, CS1
>> [memory/2]+0000000001000000 DIMM0, CS1
>> [memory/2]+0000000001100000 DIMM1, CS1
>
>> From that I would be more inclined to call bit 6 your channel selector.
>
> You have 4 CSROWs, and 2 "channels".
>
> In a real dual-channel system a CSROW covers both channels, making each
> row a double width item, that happends to cover over 2 DIMMs.
>
> I would approach it with the 4 CSROWs and 2 channels.
>
> might that make more sense?

Hmm.

I was thinking of calling them channels, but they weren't accessed in
parallel.

I think what I decided on was four CSROWs, but that they overlap, such that
dimm0.cs0.start = dimm1.cs0.start
dimm0.cs0.end = dimm1.cs0.end
dimm0.cs1.start = dimm1.cs1.start
dimm0.cs1.end = dimm1.cs1.end
BUT, dimm0.cs0.nr_pages = (dimm0.cs0.end - dimm0.cs0.start) / 2

That way, I accurately represent how much memory is in each CSROW, but I
also represent which pages might've gotten whacked by an error.

> right. You will just need to configure them so your address lookup works
> with them.

OK, I wrote an address to csrow routine.

Everything should work -- next is to test it out...

> It is basicly in its 2nd form. I  hope it is constant.  Items that
> sparked different viewpoints were removed, in the thought that the
> others were acceptable.

Excellent. Within the next few months, we shuld be ready to do a little bit
of userspace management.

Thanks for all your help. I'm pretty close now -- just need to do platform
devices for this stuff, and I'll be ready to go.

joshua

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