[Tinyos-devel] packet timestamping and packet-level timesynchronization

[Janos Sallai]

Robbie,

> it would be important for the timestamps and
> for the timesync protocol to be able to support parameterizable width
> and precision.

I agree. I will go ahead and change the PacketTimeSync interface
accordingly, i.e. I will add the width parameter, as well.

> On the timesync protocol side of
> thing, slow interrupt handling time forced us to changing the original
> flooding timesync protocol so that tx timestamps were sent out on the
> next outgoing packet instead of on the current outgoing packet since
the
> write to the outgoing tx fifo as it was going out over the air was
> something that didn't always work.  At least IMHO, it would be good
for
> the timesync interface to be able to support such an operating mode as
> it will eliminate the race condition on the packet write (arguably a
> better coding practice) while also making fewer assumptions about the
> processor's interrupt handling turn around time.  The current
interface
> might be made to support such a mode, but it's not clear if this is
> something that was intentionally supported or not.

This is a very good point. Such implementation would definitely work
with the interfaces, but I had not thought of this. It is, in fact,
equivalent to using the PacketTimestamp interface to implement the
PacketTimeSync functionality. I guess that it makes sense to change the
implementation guidelines section to describe this approach, too.

Janos

-----Original Message-----
From: Adler, Robert P [mailto:robert.p.adler at intel.com] 
Sent: Monday, May 12, 2008 4:33 PM
To: Janos Sallai
Subject: RE: [Tinyos-devel] packet timestamping and packet-level
timesynchronization

Hi Janos-

	From previous experience with timestamping on the imote2
platform, I can say that it would be important for the timestamps and
for the timesync protocol to be able to support parameterizable width
and precision.  In our case, our timebase was a 13MHz clock which caused
us to need to use 64 bit timestamps.  On the timesync protocol side of
thing, slow interrupt handling time forced us to changing the original
flooding timesync protocol so that tx timestamps were sent out on the
next outgoing packet instead of on the current outgoing packet since the
write to the outgoing tx fifo as it was going out over the air was
something that didn't always work.  At least IMHO, it would be good for
the timesync interface to be able to support such an operating mode as
it will eliminate the race condition on the packet write (arguably a
better coding practice) while also making fewer assumptions about the
processor's interrupt handling turn around time.  The current interface
might be made to support such a mode, but it's not clear if this is
something that was intentionally supported or not.

Thanks!

-Robbie

-----Original Message-----
From: tinyos-devel-bounces at millennium.berkeley.edu
[mailto:tinyos-devel-bounces at millennium.berkeley.edu] On Behalf Of Janos
Sallai
Sent: Monday, May 12, 2008 1:52 PM
To: TinyOS Development
Subject: [Tinyos-devel] packet timestamping and packet-level
timesynchronization

I am attaching two TEP drafts, one on packet timestamping, the other one
on packet-level time synchronization. Comments are welcome.

Thanks,

Janos Sallai