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Yes, it is. From: Ian Lepore To: Per Hedeland , freebsd-arm@freebsd.org Date: Fri, 09 Aug 2019 09:28:06 -0600 In-Reply-To: <69a9bed3-4d0a-f8f6-91af-a8f7d84ee307@hedeland.org> References: <69a9bed3-4d0a-f8f6-91af-a8f7d84ee307@hedeland.org> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.5 FreeBSD GNOME Team Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 464pzH60p4z3CNr X-Spamd-Bar: -- Authentication-Results: mx1.freebsd.org; none X-Spamd-Result: default: False [-2.98 / 15.00]; local_wl_from(0.00)[freebsd.org]; NEURAL_HAM_MEDIUM(-1.00)[-1.000,0]; NEURAL_HAM_SHORT(-0.98)[-0.978,0]; NEURAL_HAM_LONG(-1.00)[-1.000,0]; ASN(0.00)[asn:16509, ipnet:54.148.0.0/15, country:US] X-BeenThere: freebsd-arm@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: "Porting FreeBSD to ARM processors." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 09 Aug 2019 15:28:12 -0000 On Thu, 2019-08-08 at 22:26 +0200, Per Hedeland wrote: > On 2019-08-07 18:53, Ross Alexander wrote: > > In Message-ID: , > > someone wrote [sorry, attrib trail is a little blurry ed.]: > > > > > > Most people are not worried about their kernel clock being 200 > > > > microseconds off from UTC, even if they're using the PPS signal > > > > from a > > > > GPS receiver. So I think most people should feel completely at > > > > ease > > > > using a USB serial adapter as the input device for a PPS > > > > signal. > > > > Some people do worry, although getting PPS to work over USB is a > > fine > > first step and I'm grateful for the breadcrumb trail. > > For those that do worry, you can of course tell ntpd to correct for a > semi-fixed offset (via the 'time1' option to the 'fudge' command) - > once you know how large the offset is... More important is a low > jitter, and 20-30 microseconds seems quite good. > > @Ian, maybe it would make sense to post your test report to some NTP > forum, e.g. the comp.protocols.time.ntp newsgroup? I guess most > readers of freebsd-arm@ have little interest in using a usb-serial > adapter if they can simply use a gpio pin, with better results - but > for PCs and the like, that no longer have serial ports, it could be > very useful. > > Just last week there was a post or two to the newsgroup re-asserting > the oft-repeated claim that using a usb-serial adapter for PPS is > completely useless ("USB-to-RS-232 converters generally completely > loose the precision timing abilities of traditional serial port > circuits..."). > I posted to arm@ because a discussion here recently brought up the usb- serial performance questions, and also because I used arm hardware to craft a somewhat unique measurement apparatus for it. I have resisted joining any timing-geek newsgroups or forums for years, because it's what I do for a living as well as being a hobby, and I've always felt it would just suck another hour a day of my time if I belonged to more groups/forums that might interest me that much. :) -- Ian