From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-gy0-f171.google.com (mail-gy0-f171.google.com [209.85.160.171]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id 483E6200890 for ; Tue, 13 Mar 2012 20:05:35 -0700 (PDT) Received: by ghbz17 with SMTP id z17so2136491ghb.16 for ; Tue, 13 Mar 2012 20:05:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc:content-type; bh=z5sKOnN3wuj043EtE7N478Ej0hYjHdoB1AQdBobtFfI=; b=XugRTgAPEmYaQU96KSSuKVV2u36HefKQQPtwYgRiUDNrdqRmwORNXo+pheJhD7KGkU ECIS6Z324e6p07Eox+oWjDwBmucMHcZA3Y51hCVa+zPziQjEWqhAEMm88UM/9D015El2 B9qFfXd8RIdPNdkSH26+QfEEMdRSj+g3QRWtPB0ZpE0jIpN8KW/svFWlU12s0DkBmuw3 v68ri/F1V+XAdDNevJczaAdk2nl+UKiRDc9abJcEV1jZesxtHaNAiL+82IkHQqXByyUL nSFEcqQQnLe/cyIgVn3/qYnIoLTcRxxuBwTDSH1H4gjUJ9sEUpMujN4pt3N6VyDYuPQt ATgA== Received: by 10.182.1.104 with SMTP id 8mr1047457obl.19.1331694334109; Tue, 13 Mar 2012 20:05:34 -0700 (PDT) MIME-Version: 1.0 Received: by 10.182.68.164 with HTTP; Tue, 13 Mar 2012 20:05:14 -0700 (PDT) In-Reply-To: References: <20120313230612.GA24800@thyrsus.com> From: tz Date: Tue, 13 Mar 2012 23:05:14 -0400 Message-ID: To: Dave Taht Content-Type: text/plain; charset=ISO-8859-1 X-Mailman-Approved-At: Tue, 13 Mar 2012 20:11:18 -0700 Cc: thumbgps-devel@lists.bufferbloat.net Subject: Re: [Thumbgps-devel] Project clarification 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: Wed, 14 Mar 2012 03:05:35 -0000 A few other observations: Many of the SoCs used in the cheap routers have other on-chip perhpherals which can get us past the USB. I think I can get an Atmega to be a time-source synced to UTC. We could send an event OUT the USB host and timestamp it at the device, returning when it saw it - this might be more accurate if this is more granular than polling. We don't know yet if LinuxPPS - kernel interrupt driven timestamping is needed, but will probably be much more precise. No one has suggested turning this into a time peripheral, but that might be easier - if a microcontroller could be synced and made accurate enough (varactor like the old Heathkit clocks?) then all the gettime calls could go out to our device and get precise time. Of course the kernel could sync its time easily as well. There are faster than PPS, e.g. the Garmin 18LVx-5Hz has 5 pulses per second, at each 200mS interval, one of the 5 is the precise UTC, the others are precise too. The Sparkfun module plus either active antenna that goes with it makes it easy to receive GPS - having a dongle with a small strip antenna that you have to fiddle a lot with to get a good signal defeats the purpose. The magnetic mounts with long cables make things easy. We haven't talked much about antennas, but it is important.