[189298] in North American Network Operators' Group
Re: Cost-effectivenesss of highly-accurate clocks for NTP
daemon@ATHENA.MIT.EDU (Eric S. Raymond)
Sun May 15 06:25:48 2016
X-Original-To: nanog@nanog.org
Date: Sun, 15 May 2016 06:25:15 -0400
From: "Eric S. Raymond" <esr@thyrsus.com>
To: Bruce Simpson <bms@fastmail.net>
In-Reply-To: <57382361.8050705@fastmail.net>
Reply-To: esr@thyrsus.com
Cc: nanog@nanog.org
Errors-To: nanog-bounces@nanog.org
Bruce Simpson <bms@fastmail.net>:
> On 13/05/16 20:39, Eric S. Raymond wrote:
> >In 2012, nearly three years before being recruited for NTPsec, I
> >solved this problem as part of my work on GPSD. The key to this
> >solution is an obscure feature of USB, and a one-wire
> >patch to the bog-standard design for generic USB that exploits
> >it. Technical details on request, but what it comes down to is
> >that with this one weird trick(!) you can mass-produce primary time
> >sources with a jitter bounded by the USB polling interval for
> >about $20 a pop.
> >
> >The USB 1 polling interval is 1ms.
>
> What about USB 3.1 (assuming the device is not intended to be backwards
> compatible with the polling model) ? I should point out Intel intend to
> retire EHCI/UHCI and implement only xHCI.
Nobody makes GPSes with even USB 2 or 3 yet, and it is unlikely to happen
for a long time. Cost reasons - USB GPSes are cheap consumer-grade hardware
and the manufacturers care about fractions of a cent on the BOM.
--
<a href="http://www.catb.org/~esr/">Eric S. Raymond</a>
