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Yes, it is. To: freebsd-arm@freebsd.org References: From: Per Hedeland Message-ID: <69a9bed3-4d0a-f8f6-91af-a8f7d84ee307@hedeland.org> Date: Thu, 8 Aug 2019 22:26:44 +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: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 464KfK6Q3Gz4pq0 X-Spamd-Bar: ----- Authentication-Results: mx1.freebsd.org; dkim=pass header.d=outbound.mailhop.org header.s=dkim-high header.b=QjBCyCJv; 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 [-5.51 / 15.00]; RCVD_VIA_SMTP_AUTH(0.00)[]; HAS_XOIP(0.00)[]; TO_DN_NONE(0.00)[]; RCVD_COUNT_THREE(0.00)[3]; DKIM_TRACE(0.00)[outbound.mailhop.org:+]; NEURAL_HAM_SHORT(-0.97)[-0.968,0]; RECEIVED_SPAMHAUS_PBL(0.00)[209.157.228.81.khpj7ygk5idzvmvt5x4ziurxhy.zen.dq.spamhaus.net : 127.0.0.11]; FROM_EQ_ENVFROM(0.00)[]; MIME_TRACE(0.00)[0:+]; ARC_ALLOW(-1.00)[i=1]; IP_SCORE(-1.25)[ipnet: 52.28.0.0/16(-4.83), asn: 16509(-1.35), country: US(-0.05)]; MID_RHS_MATCH_FROM(0.00)[]; SUBJECT_HAS_QUESTION(0.00)[]; NEURAL_HAM_MEDIUM(-1.00)[-1.000,0]; R_DKIM_ALLOW(-0.20)[outbound.mailhop.org:s=dkim-high]; FROM_HAS_DN(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000,0]; MIME_GOOD(-0.10)[text/plain]; PREVIOUSLY_DELIVERED(0.00)[freebsd-arm@freebsd.org]; DMARC_NA(0.00)[hedeland.org]; ASN(0.00)[asn:16509, ipnet:52.28.0.0/16, country:US]; RCPT_COUNT_ONE(0.00)[1]; RCVD_IN_DNSWL_NONE(0.00)[28.59.28.52.list.dnswl.org : 127.0.20.0]; R_SPF_NA(0.00)[]; RCVD_TLS_ALL(0.00)[] 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: Thu, 08 Aug 2019 20:26:51 -0000 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..."). --Per