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Re: MIPS32 patches breaking DecStation

To: Harald Koerfgen <Harald.Koerfgen@home.ivm.de>
Subject: Re: MIPS32 patches breaking DecStation
From: Ralf Baechle <ralf@oss.sgi.com>
Date: Tue, 9 Jan 2001 16:28:35 -0200
Cc: linux-mips@oss.sgi.com
In-reply-to: <XFMail.010109181100.Harald.Koerfgen@home.ivm.de>; from Harald.Koerfgen@home.ivm.de on Tue, Jan 09, 2001 at 06:11:00PM +0100
References: <20010109095438.A10683@paradigm.rfc822.org> <XFMail.010109181100.Harald.Koerfgen@home.ivm.de>
Sender: owner-linux-mips@oss.sgi.com
User-agent: Mutt/1.2.5i
On Tue, Jan 09, 2001 at 06:11:00PM +0100, Harald Koerfgen wrote:

> > No problem - Done - doesnt work
> 
> Same here on my /260 (R4400SC V4.0). Neither inserting four "sll $0,$0,1" nor
> four "nop" seem to work. The branch, on the other hand, does.

Note the ssnops only make sense on superscalar CPUs, so not on the R4000.
Also note that the branch is equivalent to three nops.  One for the
branch instruction itself, the two more for instructions in the pipeline
that get killed.  On the R4600 / R500 where the hazard is only a single
instruction the branch is equivalent to only a single nop.  So while
unobvious the branch is a rather neat idea.

  Ralf

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