linux-kernel - Re: LinuxPPS low-level IRQs timestamps & ldisc

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Date:	Mon, 2 Jun 2008 13:09:16 -0400
From:	lsorense@...lub.uwaterloo.ca (Lennart Sorensen)
To:	Rodolfo Giometti <giometti@...eenne.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: LinuxPPS low-level IRQs timestamps & ldisc

On Mon, Jun 02, 2008 at 04:56:03PM +0200, Rodolfo Giometti wrote:
> I prefere avoid the if clause for getnstimeofday() since each
> instruction delay may decrease time precision, so:

Not if the delay is always constant.  That you can adjust for.  You
already have to adjust for cable length and such for your GPS, so
adjusting for a fixed delay for a conditional is no big deal.

Of course if you have to check of the DCD changed, that may not be
constant.  A check for whether this device currently has anyone that
wants the timestamp though should be a constant time.

-- 
Len Sorensen
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