Hi David,
A follow-up question on this. If I assume that there are only broadcasts
in my network I could lower this savely to 10ms without interfering with
the receive event?
cheers,
Mischa
David Moss wrote:
Ben -
You're exactly right. When energy is detected - as long as the radio thinks
it's an 802.15.4 carrier signal, the DefaultLplP module gets a signal to
wake up and listen for a few moments. I have it set to 100 ms 'listen
period' right now just for reliability reasons - i.e. maybe we have lots of
transmitters in the area and the message we're hearing right now is to
someone else, but there might be another message on the channel destined for
the local node in a moment.
Because the one shot timer is restarted, the timer fires get shifted. This
may not work so well in the future if we want to implement a synchronous
layer on top of the asynchronous layer. Instead, we'd want the asynchronous
layer to use a periodic timer to keep the synchronous layer above happy.
-David
-----Original Message-----
From: Murray, Ben [mailto:[EMAIL PROTECTED]
Sent: Thursday, September 27, 2007 7:05 AM
To: Murray, Ben; '[email protected]'; 'David Moss'
Subject: RE: [Tinyos-help] low power listening -- anomalous/random 100-200
ms delay/skew?
I think I may have found the answer to my own question :-) but I have a new
question now, but I will put that in a new e-mail
... when LPL is doing its CCACheck routine and the energyindicator signals
its .detected() event an "off" timer is started as a one shot with a
lifetime of 100 ms (set in defaultLPL.h with a definition of
DELAY_AFTER_RECEIVE 100. Assuming energy remained present in the Channel
during this time the "off" timer would be restarted. Energy is detected but
no packet was received this would simply cause a delay in the LPL routine.
Regards
Ben
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] Behalf
Of Murray,
Ben
Sent: 27 September 2007 11:18
To: '[email protected]'; 'David Moss'
Subject: [Tinyos-help] low power listening -- anomalous/random 100-200
ms delay/skew?
(TinyOS 2.0.2; Micaz; mib510; Cygwin)
I have left a number of motes running in low power listening
mode and have
observed that occasionally one or more of the motes' LPL-receive-check
experiences a sudden delay/shift of approximately 100 ms and shortly
thereafter a second sudden delay/shift of approximately
100-120 ms. I am
not running any transmitters although 2.4 GHz is quite a popular
frequency... the first time I observed it two motes
experienced the delay at
the same time after three minutes of running, the second time
I observed it
a single Mote experienced the delay after approximately half
an hour, and
this morning one of the three motes I had left running had
experienced this
delay at some point overnight. One of the three motes
experienced this
delay in all three tests, one of the motes did not experience
the delay at
all, and the third Mote experienced the delay once in the
first test but not
again. When two motes experienced the delay, they
experienced it at what
appeared to be the same time and the delay was consistent
between them.
Is there a built-in function within low power listening that
initiates a
timeout/delay-of-start with regards to the sleep interval
timer that lasts
approximately 100 ms, perhaps to cope with noisy channels or received
packets/suspected received packets? Signal detection as
opposed to a random
software/hardware error is because I have observed (using an
oscilloscope)
two motes undergoing the exact same delay at the exact same time. The
receive event is not triggered and therefore I assume that
this is some
function to deal with a suspected packet when energy is detected.
Would it be a trivial matter for me to find this function
such that I could
add an event trigger so that I know every time that LPL
detects Channel
energy but subsequently does not receive a packet (assuming
this is what is
causing the delay). Perhaps something like "FalseReceive" -
this might
allow me to correct the timing within my programme whenever this delay
occurs.
Also, if I could be directed to the exact function that would
be very useful
would as it might save me a lot of time trawling through code/editing
something incorrectly ;-)
Many thanks
Ben
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