From: Kumar Gala <kumar.gala@freescale•com>
To: <jdomogala@acmepacket•com>
Cc: linuxppc-embedded@ozlabs•org
Subject: Re: PowerPC MMU questions
Date: Fri, 12 Nov 2004 10:01:48 -0600 [thread overview]
Message-ID: <28CBA210-34C4-11D9-8B98-000393DBC2E8@freescale.com> (raw)
In-Reply-To: <NFBBJCNFKLFMBACPKDKCCEANELAA.jdomogala@acmepacket.com>
On Nov 11, 2004, at 9:36 PM, Jeff Domogala wrote:
> Folks,
>
> I am dealing with a PowerPC 7455.=A0 Here is my understanding =
regarding=20
> the
> MMU translation order:=A0 If the address is covered in a BAT, that =
BAT
> translation is in effect.=A0 If there is no BAT entry, then the page=20=
> tables
> are used to translate the address.=A0 If there is no page table =
entry,=20
> an
> exception is thrown and the exception handler for the miss needs to=20=
> add a
> new PTE.=A0 So, correct me if I'm wrong in my translation.
>
> Now, The system starts up with BAT entries to get the system off the=20=
> ground.
> I have equivalent BAT entries for the instruction and data sides.=A0 =
I=20
> also
> have the L1 I and D caches on as well as the L2 cache (I and D=20
> mode).=A0 The
> reason for using the BATs is to create non-cached I/O regions until=20=
> the MMU
> PTEs are populated.=A0 Once the MMU PTEs are setup, the caches are=20
> flsuhed and
> disabled, the MMU is disabled, the BATS disabled, the MMU re-enabled=20=
> and the
> caches re-enabled.=A0 So here are my questions:
>
> 1. Is it ok to have the same I and D BAT entries?
Yes, the I-BAT will be used for translations on instruction fetches,=20
the D-BAT will be used on data accesses (ld/st instructions).
> 2. Is it ok to setup the initial MMU PTEs with the BATs enabled or=20
> should
> the caches be disabled and MMU disabled during the PTE setup?
There should be no harm setting up MMU PTEs with BATs enabled, as you=20
said the BATs will take preference over the PTEs
> 3. Is there some other esource out there (mailing list or otherwise)=20=
> that I
> should be addressing these questions to?
This is as good as any, assuming your using linux :) Also, the=20
Freescale website has a number of App Notes on the various PPC MMUs and=20=
an email support address risc10@freescale•com
- kumar
prev parent reply other threads:[~2004-11-12 16:27 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-11-11 12:42 Which board is similar to mine, and how do I build a custom config? Peter Asemann
2004-11-11 21:15 ` Wolfgang Denk
2004-11-12 3:36 ` PowerPC MMU questions Jeff Domogala
2004-11-12 16:01 ` Kumar Gala [this message]
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