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Yes, it is. From: Ian Lepore To: Per Hedeland Cc: freebsd-arm@freebsd.org Date: Fri, 09 Aug 2019 14:17:17 -0600 In-Reply-To: <7312032d-2908-9414-0445-6b442c3a02e5@hedeland.org> References: <69a9bed3-4d0a-f8f6-91af-a8f7d84ee307@hedeland.org> <345bae77417c2495f55799b4c7ca2784f4ece9ed.camel@freebsd.org> <7312032d-2908-9414-0445-6b442c3a02e5@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: 464xP03P51z40hW X-Spamd-Bar: -- Authentication-Results: mx1.freebsd.org; none X-Spamd-Result: default: False [-2.99 / 15.00]; local_wl_from(0.00)[freebsd.org]; NEURAL_HAM_MEDIUM(-1.00)[-1.000,0]; NEURAL_HAM_SHORT(-0.99)[-0.986,0]; 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 20:17:24 -0000 On Fri, 2019-08-09 at 21:36 +0200, Per Hedeland wrote: > On 2019-08-09 17:28, Ian Lepore wrote: > > On Thu, 2019-08-08 at 22:26 +0200, Per Hedeland wrote: > > > On 2019-08-07 18:53, Ross Alexander wrote: > > > > In Message-ID: < > > > > B9EFA4D4-C1AD-4181-B421-F6BD53434FA5@dons.net.au>, > > > > 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. > > Oh, I certainly didn't intend to suggest that your message was > off-topic, only that it deserved a wider audience. > > > 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. :) > > I get your point - in particular posting a "controversial" message to > any *-geek forum can be extremely time-consuming if you try to > address > all the responses it will generate. > > Personally, although I tinkered a lot with NTP back in the days when > computers had serial ports, and even before they had Internet access, > I can't say that I've ever qualified as a true timing-geek - I still > follow the trickle of posts in the abovementioned newsgroup, but it > was probably years since I last posted anything. Would you object to > me posting an article with a *link* to your message > (i.e. > https://lists.freebsd.org/pipermail/freebsd-arm/2019-August/020263.html > ) > in the newsgroup? > > --Per > It might be better to use the link to the copy I sent to the freebsd- usb list, since it's more directly on-topic: https://lists.freebsd.org/pipermail/freebsd-usb/2019-August/016078.html I also think it would be wise to add a caveat that the results are for FreeBSD. I would expect linux performance to be similar. But for Windows, all bets are off; Windows drivers for usb-serial devices are said to vary wildly in quality depending on the vendor. -- Ian