ppc LE questions (seeking help hand info pointers)

Mark Salisbury mbs at mc.com
Fri Sep 21 06:19:18 EST 2001

Holger Bettag wrote:

> Mark Salisbury <mbs at mc.com> writes:
> [... linux in ppc little endian mode ...]
>>well, this is in the context of a multi-CPU type (x86/ppc, sparc/ppc,
>>ppc/ppc, mips/ppc) shared memory multicomputer.
>>when dealing w/ direct mapped, shared memory, uniformity of endian-ness
>>makes many multicomputer problems easier to solve.(not to mention easier
>>for the customer to program...)
> You are aware that a PPC in little endian mode is merely tricking with the
> low order address bits, but does not actually lay out its data in a little
> endian fashion in physical memory?

not according to section 3.1 of the motorola ppc "green book"

according to that it is a sort of munged le representation,

which thanks to a "one trick pony" PCI bridge looks like standard LE to
the PCI based  x86 host.

understand please that what I am proposing is a config option. as a
sub-architecture port.  it would not affect any code that it didn't
absolutely need to, and would only be compiled if sombody selected that
particular config.

I am _NOT_ suggesting running pmacs in LE mode.

as in:
      |-- PREP
      |-- CHRP
      |-- MAC
      |-- MERCURY ---
                    |-- Big Endian
                    |-- Little Endian

**   Mark Salisbury | Mercury Computer Systems    **
**   mbs at mc.com     | System OS - Kernel Team     **
**         Infinite Justice is niether.           **

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