From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ob0-f171.google.com (mail-ob0-f171.google.com [209.85.214.171]) (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 BF0DE2020B8 for ; Tue, 1 May 2012 19:13:15 -0700 (PDT) Received: by obfk16 with SMTP id k16so546073obf.16 for ; Tue, 01 May 2012 19:13:14 -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; bh=Toys7SNNFVk4AJz+G0db3Aai6hzLCxJAJB/5SiBQ/UU=; b=BulYuyXnSrcdjdccJw8MzxpXbKrqCd2k3YShUpa0aIVpoVpvMifKyBjF6zHJO45Ipe P2ZUdPEHbV13tY/k/xMCmMttJFQOIknWBXAtVrtw9TTU2eijcYIJzzZ6J81rN+pe5Us2 FVAQI03o2lWODlYKQMC4nS0ZPKpPlouqKBzP9FyPRmoVCu8hRcIH3DXOz9row0PCMNWe VARj9D1v1HwysCmeTCK6PAOAAXXY3H1WPTctbksVi4x9bUFHeFd3mol7VaCTHiVvf2SR ipFyWZ5/5QuEZrY5vHV4SRZIk7GN/gccBbzq8wfNhe14MfDoX890s/+JfjUlEEAWpLNz dPFA== MIME-Version: 1.0 Received: by 10.182.183.73 with SMTP id ek9mr11775976obc.15.1335924793909; Tue, 01 May 2012 19:13:13 -0700 (PDT) Received: by 10.182.113.40 with HTTP; Tue, 1 May 2012 19:13:13 -0700 (PDT) Received: by 10.182.113.40 with HTTP; Tue, 1 May 2012 19:13:13 -0700 (PDT) In-Reply-To: <20120502013215.GB11394@thyrsus.com> References: <20120320121724.GA11523@thyrsus.com> <20120320104542.0eaf179c.gem@rellim.com> <20120501151027.44487e16.gem@rellim.com> <20120501230917.GE10188@thyrsus.com> <20120501163302.575890f8.gem@rellim.com> <20120502013215.GB11394@thyrsus.com> Date: Tue, 1 May 2012 22:13:13 -0400 Message-ID: From: tz To: esr@thyrsus.com Content-Type: multipart/alternative; boundary=f46d04478a31c9a09c04bf043afe Cc: thumbgps-devel@lists.bufferbloat.net, gpsd-dev@nongnu.org Subject: Re: [Thumbgps-devel] Progress on Plain Jane 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, 02 May 2012 02:13:16 -0000 --f46d04478a31c9a09c04bf043afe Content-Type: text/plain; charset=ISO-8859-1 If you start to go too exotic, then an Arduino with ethernet shield emitting a packet right at the pps starts to look good, and the parts are at Radio Shack. But any such not in quantity would be more expensive. There are plenty of generic usb 2.0 chips and acm or cdc is just a set of bit and endpoint specs. And any 2.0 chip would need to use an existing linux driver unless someone plans to do a lot of libusb coding. The base problem is hardware lameness. Polling instead of an interrupt pin that can immediately respond, much less something like an input capture. I could probably sync a 2ppm dallas semiconductor i2c real time clock's 1Hz output, but even then there is nothing to sync that with the internal clocks. (I was already inspired to use pps to create an accurate synced timestamp for j1850 data off my motorcycle - oh, and batchpcb.com can do small quantities of small boards themselves cheap, but you still need to build them). If you have a 2nd usb port and want to get tricky, the pnp/insert/remove event is likely higher priority, so with a FET... On May 1, 2012 9:32 PM, "Eric S. Raymond" wrote: > Gary E. Miller : > > > That's excellent news. 0.5msec jitter is as good as we could have > > > expected and exactly what one would predict from a max error of 1msec > > > due to polling interval. The long-term NMEA/USB drift is consistent > > > with previous observations by Hal Murray and myself. > > > > Nice when theory and practice agree. I wonder if there is a USB 2.0 > > equivalent of the PL2303 which would give us a 125 microSec poll? > > > > Might be worth asking navisys about that. > > Maybe. But that would require that they qualify a new and probably more > expensive adapter part. We should get this puppy shipping and let them > see some ROI before we push that. > -- > Eric S. Raymond > > _______________________________________________ > Thumbgps-devel mailing list > Thumbgps-devel@lists.bufferbloat.net > https://lists.bufferbloat.net/listinfo/thumbgps-devel > > --f46d04478a31c9a09c04bf043afe Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable

If you start to go too exotic, then an Arduino with ethernet shield emit= ting a packet right at the pps starts to look good, and the parts are at Ra= dio Shack.=A0 But any such not in quantity would be more expensive.=A0 Ther= e are plenty of generic usb 2.0 chips and acm or cdc is just a set of bit a= nd endpoint specs.=A0 And any 2.0 chip would need to use an existing linux = driver unless someone plans to do a lot of libusb coding.

The base problem is hardware lameness.=A0 Polling instead of an interrup= t pin that can immediately respond, much less something like an input captu= re.=A0 I could probably sync a 2ppm dallas semiconductor i2c real time cloc= k's 1Hz output, but even then there is nothing to sync that with the in= ternal clocks.=A0 (I was already inspired to use pps to create an accurate = synced timestamp for j1850 data off my motorcycle - oh, and batchpcb.com can do small quantities of small boards t= hemselves cheap, but you still need to build them).

If you have a 2nd usb port and want to get tricky, the pnp/insert/remove= event is likely higher priority, so with a FET...

On May 1, 2012 9:32 PM, "Eric S. Raymond&qu= ot; <esr@thyrsus.com> wrote:
Gary E. Miller <gem@rellim.com>= :
> > That's excellent news. =A00.5msec jitter is as good as we cou= ld have
> > expected and exactly what one would predict from a max error of 1= msec
> > due to polling interval. The long-term NMEA/USB drift is consiste= nt
> > with previous observations by Hal Murray and myself.
>
> Nice when theory and practice agree. =A0I wonder if there is a USB 2.0=
> equivalent of the PL2303 which would give us a 125 microSec poll?
>
> Might be worth asking navisys about that.

Maybe. =A0But that would require that they qualify a new and probably more<= br> expensive adapter part. We should get this puppy shipping and let them
see some ROI before we push that.
--
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0<a href=3D"http://www.catb.org/~esr/">Eric= S. Raymond</a>

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