riscy
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Re: PING...

To: tthorn@daimi.aau.dk
Subject: Re: PING...
From: Daniel.Veillard@imag.fr (Daniel Veillard)
Date: Wed, 24 Nov 93 11:51:10 +0100
Cc: Multiple recipients of list <riscy@sunsite.unc.edu>
In-reply-to: Your message of "Wed, 24 Nov 93 05:19:10 EST." <199311241016.AA01413@avignon.daimi.aau.dk>
>Just to comment a *very* **very** old discussion on endian:
>It seems, contrary to what was said at some point, that we actually
>*can* switch endian more-or-less on the fly.
>
>p. 5-6 in R4000 User's Manual the status register is described.
>Bit RE: Reverse Endian in User Mode:
>  "The Reverse Endian (RE) bit, bit 25, is used to reverse the endianness
>   of the machine in User mode. R-Series processors are configured as
>   either Little-endian or Big-endian at system reset. This selection is
>   used in Kernel and Supervisor modes, and in the User mode when the
>   RE bit is 0; setting this bit to 1 inverts the selection in User mode."
>
>What endian is selected at reset on motherboards targeted at Win-NT?

   Win-NT HAL set the R4000 in little endian mode (presumably to
provide better interroperability with PC based Windows), while
UNIX implementation usually put the board in big endian mode :-) . 
   Using the RE bit seems tricky since you have an user application
running little endian and the OS (in Kernel and Supervisor space)
running big endian. Each system call should be checked to change
the endianness of the parameters if needed !

  my 2 centimes (approx 0.003 $),

Daniel
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