On Wed, May 18, 2011 at 02:31:17AM -0700, Chris Crase wrote:
> Quick question....   Is there a common time stamp between all the
> sensor data? Or does each sensor keep track of its own Hz rate and own
> time stamp? Also if it is common, what is the time time stamp?

Hi Chris!

That's actually an open question. We haven't decided yet how to handle
timestamping. Since we have the sensors scattered across several
microcontrollers, maintaining a common timebase is kind of a pain. We've
considered some possibilities though:

1. As long as all the sensors are attached using USB, the host will
   broadcast a start-of-frame packet to them all once per millisecond.
   We can use that as a semi-precise common time source.

2. If we have a working GPS receiver: many receivers can produce a 1MHz
   clock pulse that's synchronized to GPS time. Andrew has talked about
   routing that signal to all the sensor nodes as a high-precision,
   high-accuracy common time source.

3. I think Theo had found an NTP-like protocol we could use in this
   setting, but I don't remember the details.

I assume you're asking because both Kalman and Bayesian Particle Filters
need to know how far forward to run the physics/dynamics model before
checking a new sensor measurement?

(I'm sending this to the psas-team list because it should get discussed
with the rest of the team. You might want to subscribe to that list:
http://lists.psas.pdx.edu/mailman/listinfo/psas-team)

Jamey

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