From owner-freebsd-arm@freebsd.org Thu Aug 15 22:03:02 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 A9E98B7DEE for ; Thu, 15 Aug 2019 22:03:02 +0000 (UTC) (envelope-from rwa@athabascau.ca) Received: from NAM04-SN1-obe.outbound.protection.outlook.com (mail-eopbgr700053.outbound.protection.outlook.com [40.107.70.53]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-SHA384 (256/256 bits)) (Client CN "mail.protection.outlook.com", Issuer "GlobalSign Organization Validation CA - SHA256 - G3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 468gS41GTdz4Tb3 for ; Thu, 15 Aug 2019 22:02:59 +0000 (UTC) (envelope-from rwa@athabascau.ca) ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=gBvrWF5yd1r6/Zc+uC3h/IiEaRQJd0bOGxgJmGBedGnFTCP5DPqBJmVVWMN1l2VtHW/2O4zlviD9rqrS4o0mruCsHq97KiSwQhAlNwCCkcSCRsrOicOhWcp5zDm+EckynLVTJ2KMp8TYHvPOQaPeIt7JH6HMku090YqWueZYBsrm8lYIsfJsrzjRoJQ7o3q7y+6nvr6ICINvYAVQeTGyZx7r7eQ4IFe26NdixFT1rfP6l5U1FG+/ziXU87jBwWfyVFKwAR4CZO2DUkPHRQXlvz4ThgduePKbMEHlBy1lWk+5fRh7Pxumd7QWf2JMcsfM5ccFUbkq18Ujv7GFAH0Ziw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector9901; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=iT/WITpz4reRS44+hwQrGD61EOjjVTxZk0uO5uRh/Hs=; b=WT+qlPIqGMqm6IGxCWWs3FKIdqMK1Kpk4tc6cfTdIRW8s9dm3b4k9M0ES2FYT7N6AQtfVfvqSdXzQs/9FhmpYhrYc+IybDiN2zGD3aHUP+TBJvkV7/E9HSLdAd4pFajAS5yp9GMOXQye9BjCA1Kso4AxauO2dp5j8i7u+Dh3cXMomYRwiRXVGhqrWMt/F99vvDKfSHFoXZiX40ni1KFmmInaDYXKLX6JSq4QfHkVwZIpEycibMVriTeHLlMGnRnoOgH0/hqbMGjCzNfTHlA36IRnyGW+xrfjhefnsAIwhNe69w5N5j7yM8dYY2vhuoj1uTurZiGZAGrazr6tgGU0Jw== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass (sender ip is 131.232.32.37) smtp.rcpttodomain=freebsd.org smtp.mailfrom=athabascau.ca; dmarc=bestguesspass action=none header.from=athabascau.ca; dkim=none (message not signed); arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=austaff.onmicrosoft.com; s=selector2-austaff-onmicrosoft-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=iT/WITpz4reRS44+hwQrGD61EOjjVTxZk0uO5uRh/Hs=; b=2iX3RJOYNrWDy1MpNadwx8shNXuYiCNZuZsD23xEBhsDmHEDIh6hkHdHRnl44ki6j1+zkhaXmZGuIHxlpslB9hNEWPv4X6oAoPWhm7cw9sZaDkRGibemNTj/1mdxYYF/Ekp79bpCcxCdmniuo5McHj5EHWbLXWN/QSsU1HylYgI= Received: from CY4PR13CA0024.namprd13.prod.outlook.com (2603:10b6:903:32::34) by CY4PR13MB1126.namprd13.prod.outlook.com (2603:10b6:903:a0::14) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.2178.15; Thu, 15 Aug 2019 22:02:57 +0000 Received: from TO1CAN01FT015.eop-CAN01.prod.protection.outlook.com (2a01:111:f400:7e5d::200) by CY4PR13CA0024.outlook.office365.com (2603:10b6:903:32::34) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id 15.20.2199.6 via Frontend Transport; Thu, 15 Aug 2019 22:02:57 +0000 Received-SPF: Pass (protection.outlook.com: domain of athabascau.ca designates 131.232.32.37 as permitted sender) receiver=protection.outlook.com; client-ip=131.232.32.37; helo=smtp-relay.cs.athabascau.ca; Received: from smtp-relay.cs.athabascau.ca (131.232.32.37) by TO1CAN01FT015.mail.protection.outlook.com (10.152.122.72) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id 15.20.2178.16 via Frontend Transport; Thu, 15 Aug 2019 22:02:56 +0000 Received: from autopsy.pc.athabascau.ca (autopsy.pc.athabascau.ca [131.232.4.80]) by smtp-relay.cs.athabascau.ca (Postfix) with ESMTPS id 12EC6200F8 for ; Thu, 15 Aug 2019 16:02:56 -0600 (MDT) Date: Thu, 15 Aug 2019 16:02:56 -0600 (MDT) From: Ross Alexander X-X-Sender: rwa@autopsy.pc.athabascau.ca To: freebsd-arm@freebsd.org Subject: Re: Is it a good idea to use a usb-serial adapter for PPS? Yes, it is. 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List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 15 Aug 2019 22:03:02 -0000 In <24b0eaf25b64d6098b390df092866c69e352d859.camel@freebsd.org>, Ian Lepore writes: > [... ed.] I arranged to use a very stable nearly-drift-free > frequency source instead of a cheap crystal for counting time in the > kernel. You have my complete and focussed attention. Say on. > [WRT USB 2, ed.] the polling happens in time slots that are 125 > microseconds wide. There's just no reason for a lot of jitter or > latency. 125 microseconds is a lot of jitter. Latency is a don't care, you can fudge that out. Looking at a Pi 1b+, running some consumer grade Ublocks GPS module, a five year old Linux, and with a view of only half the sky (but using PPS on a GPIO pin): > autopsy:/u0/rwa > ntpq chime > > ntpq> lpee > remote refid st t when poll reach delay offset j= itter > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D > oPPS(0) .PPS. 0 l 8 16 377 0.000 0.001 = 0.002 > *SHM(0) .GPS. 5 l 6 16 377 0.000 419.464 31= 0.013 > > ntpq> rl &1 > associd=3D10146 status=3D911a conf, reach, sel_falsetick, 1 event, sys_pe= er, > srcadr=3DPPS(0), srcport=3D123, dstadr=3D127.0.0.1, dstport=3D123, leap= =3D00, > stratum=3D0, precision=3D-20, rootdelay=3D0.000, rootdisp=3D0.000, refid= =3DPPS, > reftime=3De1005453.fffff7a5 Thu, Aug 15 2019 15:59:47.999, > rec=3De1005454.debc0ef4 Thu, Aug 15 2019 15:59:48.870, reach=3D377, > unreach=3D0, hmode=3D3, pmode=3D4, hpoll=3D4, ppoll=3D4, headway=3D0, fla= sh=3D00 ok, > keyid=3D0, ttl=3D0, offset=3D0.001, delay=3D0.000, dispersion=3D0.233, > jitter=3D0.002, > filtdelay=3D 0.00 0.00 0.00 0.00 0.00 0.00 0.00 = 0.00, > filtoffset=3D 0.00 0.00 0.00 0.00 0.00 0.00 0.00 = 0.00, > filtdisp=3D 0.00 0.24 0.48 0.72 0.96 1.20 1.44 = 1.68 > > ntpq> rl > associd=3D0 status=3D0413 leap_none, sync_uhf_radio, 1 event, spike_detec= t, > version=3D"ntpd 4.2.7p397@1.2483-o Sun May 3 05:32:19 UTC 2015 (1)", > processor=3D"armv7l", system=3D"Linux/4.1.12-v7+", leap=3D00, stratum=3D6= , > precision=3D-19, rootdelay=3D0.000, rootdisp=3D733.955, refid=3DSHM(0), > reftime=3De1005456.debbfb5d Thu, Aug 15 2019 15:59:50.870, > clock=3De100545c.084cd64c Thu, Aug 15 2019 15:59:56.032, peer=3D10147, t= c=3D4, > mintc=3D3, offset=3D0.000921, frequency=3D0.047, sys_jitter=3D310.013202, > clk_jitter=3D0.000, clk_wander=3D0.000 The jitter is expressed in units of 1 millisecond, unless I am badly mistaken; for which possibility I apologize in advance. (as an aside, has editing quotation text gone utterly out of style? Present company excepted, of course.) regards, Ross =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D Ross Alexander, (780) 675-6823 desk / (780) 689-0749 cell, rwa@athabascau.c= a 54.71593 N 113.30835 W Order is simply a thin, perilous condition we try to impose on the basic reality of chaos. -- William Gaddis, _J R_ -- This communication is intended for the use of the recipient to whom it is a= ddressed, and may contain confidential, personal, and or privileged informa= tion. Please contact us immediately if you are not the intended recipient o= f this communication, and do not copy, distribute, or take action relying o= n it. Any communications received in error, or subsequent reply, should be = deleted or destroyed. ---