From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-vx0-f171.google.com (mail-vx0-f171.google.com [209.85.220.171]) (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 BF49D20069D for ; Wed, 14 Mar 2012 11:22:23 -0700 (PDT) Received: by vcbfl15 with SMTP id fl15so4476933vcb.16 for ; Wed, 14 Mar 2012 11:22:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; bh=i2QH+1ySnwYRWEy5ckdjgrghWgmjs8gAuw4YiQsx4gc=; b=vzqlh8509bNsq4i+n9g+4FWd83sGuXcqwTCw+Bq1xhq/yHqeHLuDVVek98OdvXAzDO D6az5OgtyJjD/AXKs9ZB8TenHOUTP5Gl8gzjPONnyMw6sq1GwfL9ScQkoigOOsXYfHmq xcggIU9tcnezJnVcAYBd2WRMsvejUwrXgXOPRumP0vDGiX3GW/h76U6oM8pmBExbyHx+ ce2GPsFrtMs87ZRjrKidKuAMJ6Bd+iMpw9zktkvtLbVtEO9tLaEBqyf8wvIk5FpMCkVO oql7B7bSbx9WTvjeSBt+yGNzzGOCCTgESYcMollRDTkkHbRhoIkQIRd8B1PfYhTFrmXf JN0w== MIME-Version: 1.0 Received: by 10.52.93.179 with SMTP id cv19mr2599153vdb.103.1331749342462; Wed, 14 Mar 2012 11:22:22 -0700 (PDT) Received: by 10.220.140.132 with HTTP; Wed, 14 Mar 2012 11:22:22 -0700 (PDT) In-Reply-To: References: Date: Wed, 14 Mar 2012 13:22:22 -0500 Message-ID: From: Patrick Maupin To: tz Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Cc: thumbgps-devel@lists.bufferbloat.net Subject: Re: [Thumbgps-devel] Raspberry PI on Piday; better yet, generate our own system tick with a PPS synced PLL 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 18:22:24 -0000 On Wed, Mar 14, 2012 at 12:59 PM, tz wrote: > The ethernet port is USB based and has a USB connector, Hm, yet more latencies to characterize. If one of the USB ports is OTG, maybe we could just use a Linux gadget device interface and have this connect to the router through USB? > Better yet, we can move the system tick itself off to a GPIO pin > causing an interrupt, and use a PLL frequency multiplier that syncs > exactly to 100x (or 1000x) the PPS. =A0The PPS could be a second > interrupt if there was no other easy way to indicate the UTC boundary > from the other pulses. =A0The GPIO interrupt can sample the internal > clock and do what it needs for the sub-tick timing. =A0I don't know > which other peripherals, but maybe they could read the sub-tick or > even the "time of day in microseconds" from our system over I2C or > SPI. > > This could be a fairly simple circuit (worries about noise, drift...), > or there's a chip... Yes, there are lots of chips available for this sort of thing. Probably don't need anything too fancy.