From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from liara.ita.chalmers.se (liara.ita.chalmers.se [129.16.226.167]) (using TLSv1 with cipher AES128-SHA (128/128 bits)) (Client CN "liara", Issuer "liara" (not verified)) by huchra.bufferbloat.net (Postfix) with ESMTPS id 213A42002DE for ; Tue, 3 Apr 2012 10:20:41 -0700 (PDT) Received: from bridge1.fy.chalmers.se (129.16.110.161) by smtp.chalmers.se (129.16.10.240) with Microsoft SMTP Server (TLS) id 14.1.355.2; Tue, 3 Apr 2012 19:20:37 +0200 Date: Tue, 3 Apr 2012 19:20:32 +0200 From: =?ISO-8859-15?Q?H=E5kan_Johansson?= X-X-Sender: htj@bridge1.fy.chalmers.se To: "Eric S. Raymond" In-Reply-To: <20120403143402.GA7338@thyrsus.com> Message-ID: References: <20120403143402.GA7338@thyrsus.com> User-Agent: Alpine 2.00 (DEB 1167 2008-08-23) MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="276930926-1169172653-1333473637=:13879" X-Originating-IP: [129.16.110.161] X-Mailman-Approved-At: Tue, 03 Apr 2012 12:59:53 -0700 Cc: thumbgps-devel@lists.bufferbloat.net, gpsd-dev@nongnu.org Subject: Re: [Thumbgps-devel] [gpsd-dev] "Plain Jane" timing GPS is working! X-BeenThere: thumbgps-devel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 03 Apr 2012 17:20:42 -0000 --276930926-1169172653-1333473637=:13879 Content-Type: text/plain; charset="ISO-8859-15"; format=flowed Content-Transfer-Encoding: 8BIT Is it the pulse shape (i.e. length) or the pulse repetition that gpsd rejects? As I recall, a SiRf-III GPS delivers a PPS pulse that is only 1 us long, so does not record a full state change, but this is handled. Timing over USB is distored by the inherent USB polling interval of 1 ms, so could make the inter-pulse interval fail those tests. (They actually allow +/-1 ms, so should make it?). Logfile? Due to the USB effectively downsampling the measurement to the USB 'polling clock', such a setup might be prone to seeing jumps. I.e. if the USB polling frequency is close to a multiple of the PPS signal, then it for long times drifts slowly (which will not be detected), and then jumps one polling cycle. (Possibly even usable. Unhandled it could make life miserable for chrony/ntp.) Cheers, Håkan On Tue, 3 Apr 2012, Eric S. Raymond wrote: > A few minutes ago I received mail from the test engineers at NaviSys. > They have tested the "Plain Jane" concept (take a stock SiRf-III GPS > chip plus PL2303 USB adapter, connect the 1PPS pin on the former to > DCD input on the latter) with GPSD, and are actually seeing PPS pulse > messages in the logs. > > The filter in GPSD doesn't like the pulse shape and is rejecting it, but > that can be fixed. The essential point is that the hardware mod works > exactly as expected and is producing events visible on USB. > > I'm expecting my samples from UniTraq today or tomorrow and may soon have > more good news about our second Plain Jane variant. > -- > Eric S. Raymond > > --276930926-1169172653-1333473637=:13879--