From owner-freebsd-arm@freebsd.org Fri Aug 9 19:36:17 2019 Return-Path: Delivered-To: freebsd-arm@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id C184FCFB32 for ; Fri, 9 Aug 2019 19:36:17 +0000 (UTC) (envelope-from per@hedeland.org) Received: from outbound1f.eu.mailhop.org (outbound1f.eu.mailhop.org [52.28.59.28]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) server-signature RSA-PSS (4096 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 464wTX4vkbz3R5y for ; Fri, 9 Aug 2019 19:36:16 +0000 (UTC) (envelope-from per@hedeland.org) ARC-Seal: i=1; a=rsa-sha256; t=1565379375; cv=none; d=outbound.mailhop.org; s=arc-outbound20181012; b=plz/ZL9590Cf8ISbszgPVN79PlaThG94/+B2RTY6ObZY2rZ8vAQ0VKch2nYeI3+uBjYqqPcEmFRqf R0AgBkUwwDE+AQnZuVOH7dNB6sfV66bsuSsPHucSCS1W3/1XkQBt3KMPoynhcWzdSToFKcOFxf7qxA nZEKlg6B9oJsezFKurBP3F6S6yrLgjkdD2FgQGB4XGfRn/ZKEP/QxWrdV8fQIFSebWJd/S3NhINeXk t+zHAfArHqE6pWaMQYY4/b49+zjMpNZrJvSsrDhdOG5YJAplI4Vl640BRYjBeK0R0qkND3HGpa9sie U3T2wx+z6IPUqVLNvQ/fW64pkFDzUPg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=outbound.mailhop.org; s=arc-outbound20181012; h=content-transfer-encoding:content-type:in-reply-to:mime-version:date: message-id:from:cc:references:to:subject:dkim-signature:from; bh=o2/oDp1xxmOYG059mHBzfNx5i2RdVJt1Wu8KYTZD6Qc=; b=dTlOgndXMTF2sUsF2XUoceBwXg9v2k+TV5bLU7Bgsj8zu/dwsezdI2M2I/jYxNCA/Twckg1GNs5WA Fdem4V7B/UA+R7+lwGBjkCKkU14pRPVnlV1MIHxTEpjkaH87X8V+UTOz6QUVvFR2C0lvInDAwLdsdh xjAxsQ84jjduB86wgWkrGtMEcUvP2H2jkZaGLSY+cfmDb+WIvABzJc8ODNjK/FfDjJPmOLfO7cn9OG gb4jEzFfdnNs+omwwLp9wQ/3zg3g9de9Ak6/f7NN2Fyqsn1BmfJqAz2HWhAIa623PrHlmLwm8bWfsS RPdYZchtVTRR/jYcgBUBisiZBo1gMBQ== ARC-Authentication-Results: i=1; outbound2.eu.mailhop.org; spf=none smtp.mailfrom=hedeland.org smtp.remote-ip=81.228.157.209; dmarc=none header.from=hedeland.org; arc=none header.oldest-pass=0; DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=outbound.mailhop.org; s=dkim-high; h=content-transfer-encoding:content-type:in-reply-to:mime-version:date: message-id:from:cc:references:to:subject:from; bh=o2/oDp1xxmOYG059mHBzfNx5i2RdVJt1Wu8KYTZD6Qc=; b=RrYSnqxmQekQef/UPSgRbGmfprOPGQwMfgzmRA6DsBdlOWkDjYpZ66skkESAmE6E427IJVNZjstz6 FsJfNFPoFSojcXIjljRGA8erqTf7gF+pfNQUaAXosmiIF1Skms4HoViRp53eL9ufau+p1zH3rLw4GV 1UUqwt5uS34OJAT+5NhbBIlaUruWHlTH6xWepFxBxBrNBR6M9pdme1euTR4UB1aGgGPA+AIo95paUT iZiCjHrctDQ13T1kYlzCN4AgigcAkFVK5eQB8du1jtAITm6KxMC2w+ij7MMcawIeTRMldqXPziQ060 XLgy845SEgF8pGyqOolQC+fOIw8ZQXA== X-MHO-RoutePath: cGVyaGVkZWxhbmQ= X-MHO-User: f14e0e13-badc-11e9-a203-f5e3bb5d0a28 X-Report-Abuse-To: https://support.duocircle.com/support/solutions/articles/5000540958-duocircle-standard-smtp-abuse-information X-Originating-IP: 81.228.157.209 X-Mail-Handler: DuoCircle Outbound SMTP Received: from hedeland.org (unknown [81.228.157.209]) by outbound2.eu.mailhop.org (Halon) with ESMTPSA id f14e0e13-badc-11e9-a203-f5e3bb5d0a28; Fri, 09 Aug 2019 19:36:12 +0000 (UTC) Received: from pluto.hedeland.org (pluto.hedeland.org [10.1.1.5]) by tellus.hedeland.org (8.15.2/8.15.2) with ESMTPS id x79JaBi8019079 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NO); Fri, 9 Aug 2019 21:36:11 +0200 (CEST) (envelope-from per@hedeland.org) Subject: Re: Is it a good idea to use a usb-serial adapter for PPS? Yes, it is. To: Ian Lepore References: <69a9bed3-4d0a-f8f6-91af-a8f7d84ee307@hedeland.org> <345bae77417c2495f55799b4c7ca2784f4ece9ed.camel@freebsd.org> Cc: freebsd-arm@freebsd.org From: Per Hedeland Message-ID: <7312032d-2908-9414-0445-6b442c3a02e5@hedeland.org> Date: Fri, 9 Aug 2019 21:36:11 +0200 User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <345bae77417c2495f55799b4c7ca2784f4ece9ed.camel@freebsd.org> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 464wTX4vkbz3R5y X-Spamd-Bar: ----- Authentication-Results: mx1.freebsd.org; dkim=pass header.d=outbound.mailhop.org header.s=dkim-high header.b=RrYSnqxm; dmarc=none; spf=none (mx1.freebsd.org: domain of per@hedeland.org has no SPF policy when checking 52.28.59.28) smtp.mailfrom=per@hedeland.org X-Spamd-Result: default: False [-5.54 / 15.00]; RCVD_TLS_ALL(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; R_DKIM_ALLOW(-0.20)[outbound.mailhop.org:s=dkim-high]; HAS_XOIP(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; NEURAL_HAM_MEDIUM(-1.00)[-1.000,0]; NEURAL_HAM_LONG(-1.00)[-1.000,0]; MIME_GOOD(-0.10)[text/plain]; DMARC_NA(0.00)[hedeland.org]; RCVD_COUNT_THREE(0.00)[3]; TO_MATCH_ENVRCPT_SOME(0.00)[]; DKIM_TRACE(0.00)[outbound.mailhop.org:+]; RCPT_COUNT_TWO(0.00)[2]; RCVD_IN_DNSWL_NONE(0.00)[28.59.28.52.list.dnswl.org : 127.0.20.0]; NEURAL_HAM_SHORT(-0.99)[-0.993,0]; RECEIVED_SPAMHAUS_PBL(0.00)[209.157.228.81.khpj7ygk5idzvmvt5x4ziurxhy.zen.dq.spamhaus.net : 127.0.0.11]; R_SPF_NA(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; MIME_TRACE(0.00)[0:+]; IP_SCORE(-1.25)[ipnet: 52.28.0.0/16(-4.85), asn: 16509(-1.35), country: US(-0.05)]; ASN(0.00)[asn:16509, ipnet:52.28.0.0/16, country:US]; MID_RHS_MATCH_FROM(0.00)[]; SUBJECT_HAS_QUESTION(0.00)[]; ARC_ALLOW(-1.00)[i=1] 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 19:36:17 -0000 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: , >>> 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