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From: "Eric S. Raymond" <esr@thyrsus.com>
To: tz <thomas@mich.com>
Cc: thumbgps-devel@lists.bufferbloat.net
Subject: Re: [Thumbgps-devel] Jitter and latency in a linux system might be a problem. Minimal BoM crosspost.
Date: Mon, 12 Mar 2012 17:08:31 -0400	[thread overview]
Message-ID: <20120312210831.GA17895@thyrsus.com> (raw)
In-Reply-To: <CAFv7Oih1+0hMRCJmRn33sy9O-NaYOjYVb-WKABd81yptvi1Wrg@mail.gmail.com>

tz <thomas@mich.com>:
> The PPS change detect thread in gpsd might have latency problems if
> the kernel is busy and/or it isn't a high priority - a plain userland
> program shows about 1mS jitter - a loop with the ioctl to block until
> a pin-change followed by gettimeofday will vary over about a 1000 uS
> band on my dual-core netbook.  If you really need 100nS, you might
> need to use the kernel PPS, preferably with a dual core or better CPU
> so the interrupt can capture the nanosecond timer reliably.

We don't need 100ns.  Our target accuracy is 1ms.  This simplifies
things a lot.
-- 
		<a href="http://www.catb.org/~esr/">Eric S. Raymond</a>

      parent reply	other threads:[~2012-03-12 21:08 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-03-12 19:09 tz
2012-03-12 20:44 ` Patrick Maupin
2012-03-12 21:02   ` tz
2012-03-12 21:22     ` Eric S. Raymond
2012-03-12 21:08 ` Eric S. Raymond [this message]

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