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Wolfgang Kern
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 Posted: Wed Jul 16, 2008 11:05 am Post subject: Re: 64-bit mode |
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Brendan wrote:
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Good to know that this is possible even CPU manuals state it different,
but I'd like to see my pagetables above the 1.MB.
... Basically the paging structures used during
boot are temporary and it doesn't matter a lot where the RAM comes
from...
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Yes, this makes sense.
[about CPU manuals... ]
....
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My original (3 and a half year old) opinion remains the same - it
works until someone can prove it doesn't (despite what any
documentation says).
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Right, we may always find things working which aren't documented
because even the chip developers may not know all coincident
behaviour beside strict defined functionalities.
__
wolfgang |
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Maxim S. Shatskih
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| Posted: Wed Jul 16, 2008 11:05 am Post subject: Re: 64-bit mode |
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I like to see my page tables above 4 GB (where possible), as RAM above
4 GB is the "least useful" - ie. can't be used by ISA DMA;
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16MB is the limit for ISA DMA.
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or 32-bit PCI devices
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....without the Dual Address Cycle feature.
--
Maxim Shatskih, Windows DDK MVP
StorageCraft Corporation
maxim@storagecraft.com
http://www.storagecraft.com |
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Wolfgang Kern
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| Posted: Wed Jul 16, 2008 10:23 pm Post subject: Re: 64-bit mode |
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Alexei A. Frounze wrote:
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[about CPU manuals... ]
...
My original (3 and a half year old) opinion remains the same - it
works until someone can prove it doesn't (despite what any
documentation says).
Right, we may always find things working which aren't documented
because even the chip developers may not know all coincident
behaviour beside strict defined functionalities.
Possible, but not necessarily. Not documenting something clearly and
discouraging from doing certain things has other uses:
1. fewer guarantees -> less support
2. freedom to change things later
3. covering up bugs (doesn't always work, especially retrospectively)
4. making competitors' lives harder
What's interesting is that often times not only competitors struggle
with some obscure and ambiguous things in the documentation, others do
too (if there's only one set of documentation for everyone) and that
may actually incur more support requests (unless people turn straight
to reverse engineering in those gray areas).
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Yes, we can play around with undocumented stuff, but we better
follow the recommended ways if we want our OS compatible over a
longer period. And we should perhaps more often look out for
clarify notes or newer manual releases.
But I really hope that a new chip-design wont turn out to just
make previous incomplete/wrong statements in the manuals true.
I just hope, not fully sure for it may not happen.
__
wolfgang |
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