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Date: Wed, 8 Feb 2012 17:27:07 +1000
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From: Peter Crosthwaite <peter.crosthwaite@petalogix.com>
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Subject: Re: [Qemu-devel] [RFC PATCH v2 2/4] cadence_ttc: initial version of
	device model
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To: Paul Brook <paul@codesourcery.com>
Cc: peter.maydell@linaro.org, monstr@monstr.eu, edgar.iglesias@petalogix.com, qemu-devel@nongnu.org, John Linn <john.linn@xilinx.com>, duyl@xilinx.com, linnj@xilinx.com, afaerber@suse.de, john.williams@petalogix.com

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2012/2/7 Paul Brook <paul@codesourcery.com>

> > Implemented cadence Triple Timer Counter (TCC)
>
> It looks like you're implementing a periodic timer as sequence of chained
> oneshot timers.  This is a bad idea.  In qemu interrupt latency may be
> high,
> so you're likely to suffer from significant time skew.
>
> Ok, I could implemented the wraparound event as a periodic timer and the
match events are kicked off as seperate one-shot timers when the wrap
around occurs? There would still be a small delay on match events, but it
would get rid of the integration effect of lots of little delays (over many
wrap arounds) add up to a significant skew.


> Paul
>

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<br><br><div class=3D"gmail_quote">2012/2/7 Paul Brook <span dir=3D"ltr">&l=
t;<a href=3D"mailto:paul@codesourcery.com">paul@codesourcery.com</a>&gt;</s=
pan><br><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border=
-left:1px #ccc solid;padding-left:1ex">
<div class=3D"im">&gt; Implemented cadence Triple Timer Counter (TCC)<br>
<br>
</div>It looks like you&#39;re implementing a periodic timer as sequence of=
 chained<br>
oneshot timers. =A0This is a bad idea. =A0In qemu interrupt latency may be =
high,<br>
so you&#39;re likely to suffer from significant time skew.<br>
<span class=3D"HOEnZb"><font color=3D"#888888"><br></font></span></blockquo=
te><div>Ok, I could implemented the wraparound event as a periodic timer an=
d the match events are kicked off as seperate one-shot timers when the wrap=
 around occurs? There would still be a small delay on match events, but it =
would get rid of the=A0integration effect=A0of lots of little delays (over =
many wrap arounds) add up to a significant skew.</div>
<div>=A0</div><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;=
border-left:1px #ccc solid;padding-left:1ex"><span class=3D"HOEnZb"><font c=
olor=3D"#888888">Paul<br>
</font></span></blockquote></div><br>

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