Subject: Re: ARM9 Endian mode
To: None <firstname.lastname@example.org>
From: Toru Nishimura <email@example.com>
Date: 01/27/2004 22:41:48
> I noticed that on some of the Intel XScale processors only Big endian =
> mode is allowed, so I figure the dual compatible endian mode processors =
> has to do some conversion internally in one of the modes not native to =
> the execution unit.
As long as a processor is designed in truly straight RISC discipline, there
is no chance to constraint endianess inside processor core. The core itself can
be designed endian-neutral, i.e., no hardwired endianess and "incore
conversion" back-and-forth. Mixed endianness does matter at data path
outside of core, at SoC internal-connect or at bus/peripheral-connect.
Sometimes it's hard to keep entire hardware design endian-neutral, and
more-or-less endian conversion efforts must be done either by hardware
circuit design or device driver software. Making XScale big-endian only
can not wipe out endian conversion in practice and the decision was made
by other reason(s) than "performance penalty."
Toru Nishimura/ALKYL Technology