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Re: [gpsd-dev] PPS over USB

From: Gary E. Miller
Subject: Re: [gpsd-dev] PPS over USB
Date: Sun, 6 May 2012 13:05:06 -0700

Yo Ed!

On Sun, 06 May 2012 12:54:51 +0100
Ed W <address@hidden> wrote:

> > Ugh.  The Garmin 18s are unsuitable for indoor use.  The uBlox6 in
> > the GR-601W works well in my basement.
> OK, so you could use some other serial device, my point was whether
> the jointing together needed to be better than DIY?

And I thought I made the point that DIY was not an option.  These
guys don't even own multi-meters.

> That said, I'm
> kinda curious that the ublox6 does so much better than a Garmin18,
> the theoretical specs aren't so different?

All I can say is that I have Garmin18s, SiRFIIIs, uBlox6, etc and the 
newer ones all work fine in my basement and the Garmin 18 only works
with a very open sky.

>  I have never found any
> device to work inside to be honest?  (at least not for initial
> acquisition)

Maybe yours is deeper than mine.

> > That would be fairly similar to what the bufferbloat project is
> > looking to do, except they want it also to work as a standard
> > router.
> Which bit of the above makes it unsuitable as a standard router?  Too 
> expensive?

Yes, and too DIY.  Remember these guys don't own a soldering iron, nor 
do they want use drivers different than mainstream ones.

> Just to be clear - the above is a waaay more powerful board than most 
> routers, it's i586 compatible (rather than ARM).  However, it is 
> probably more expensive than an old Linksys router, and it's
> switching capacity is almost certainly lower than a cutting edge
> Linksys job.

And that is exactly the problem.  They want a common dumb consumer
platform becasue they are looking to develop teaks for dumb consumer

> The bit I was trying to square was that the GPIOs don't currently
> have a linux driver which is interrupt triggered.

Yup, and the bufferbloat project noted that and explictly decided that
to go down that road was to go Yak Shearing.  If such a driver should
appear that might be usefull in a future project.

> > That said, I would personnally love to find a USB 2.0 equivent to
> > the USB1.1 PL2303.
> Just clicking on the first hit in google takes me to here.  Is this
> what you want?

Nope. That is just a USB to RS-232.  The problem is finding a 
matching cheap RS-232 GPS, with PPS and preinstalled RS-232 connector.

I am looking for an integrated product requiring zero hardware skills to

> It's not bad, but I think the issue is still that the USB bus is non 
> deterministic, so it might still have a good bunch of jitter around 
> that.

Actually, it is VERY deterministic.  USB 1.1 is polled 1024 times a
second, and that is exactly what we see in the results.

> Anyway, I got stalled, but my goal was quite similar.  I wanted to
> try and offer a cheap solution to Stratum 1 servers.  The idea of the
> Alix plus a cheapo serial GPS seemed very attractive.  They can be
> powered via ethernet which potentially makes them easy to put into a
> hobby box and put the whole box on the roof...

And as a pre-packaged commmercial solution it might be very interesting
to many people.  Just not the bufferbloat folks.

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97701
        address@hidden  Tel:+1(541)382-8588

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