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Re: [MIPS] Probe for usability of cp0 compare interrupt.

To: "Maciej W. Rozycki" <macro@linux-mips.org>
Subject: Re: [MIPS] Probe for usability of cp0 compare interrupt.
From: Ralf Baechle <ralf@linux-mips.org>
Date: Wed, 17 Oct 2007 18:23:45 +0100
Cc: Atsushi Nemoto <anemo@mba.ocn.ne.jp>, linux-mips@linux-mips.org
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References: <S20022491AbXJQLKE/20071017111004Z+82239@ftp.linux-mips.org> <20071018.011033.115643462.anemo@mba.ocn.ne.jp> <20071017164636.GC5491@linux-mips.org> <Pine.LNX.4.64N.0710171756450.28993@blysk.ds.pg.gda.pl>
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On Wed, Oct 17, 2007 at 06:03:35PM +0100, Maciej W. Rozycki wrote:

> > The two things are a know lose end.  There is a bug in some old MIPS
> > processors where reading one of the compare or count registers in exactly
> > the moment when both have identical values in the interrupt getting lost.
> > 
> > Will have to dig up the details on that one again before I can implement
> > a proper workaround ...
> 
>  This is the erratum #53 of the R4000PC/SC processor and it triggers if 
> the Count register is read.  Conveniently, in the errata sheet as 
> distributed, the text is covered by a figure (Figure 1a on page 13), so 
> you can only reach the page with some PostScript magic.  I did it a while 
> ago and now have a separate document available which provides the text of 
> page 13 with the figure removed.  I can provide it if there is interest.

Ah.  I noticed there was something like white writing on white background
matching when I searched the PDF for keywords.  So I guess it would be
nice if somebody could regenerate a PS or PDF file.  I also seem to be
missing information on the later R4400 versions.

  Ralf

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