I know the mica2 receives data in an interrupt, so assuming that you
haven't overrun your int timing with a bunch of other async stuff or
shut off ints for too long with atomics, it is able to buffer incoming
messages and route them to the various receiver methods. I would be
surprised if other motes did not do something like this.
What I have seen, and am just trying to quantify, is that the CSMA
backoff mechanism doesn't work as well as one would hope. So messages
that are transmitted at nearly the same time collide and are dropped
more than one would like. Again this is with the mica2's...more data
to follow when I get it together, and some using micaz's as well...
MS
Andrea Pacini wrote:
Yes this is the same problem , I think, that I have met some time ago.
The problem is that when a node sends a message the other node receives
this message ONLY IF it is not running any code.
(only in this case the receive event is triggered). It seems that the
node cannot buffer the RECEIVE event if it is running something.
So , if you want that a node receives surely a message you must write
your code so that when it should receive a message it has run
all the previous code.
It is a strange behaviour in my opinion, I don't know if it is only for
Tmote Sky (TelosB) or for all platforms.
To highlight this behaviour try these situation:
NODE A:
NODE B:
[...]
event Receive (){ call Leds.redOn(); }
call Send(); // sends something
StdControl.start () { }
[....]
Node B does nothing; it only waits for A message. Clearly, it receives
the message from A.
Now try these:
NODE A:
NODE B:
[...]
event Receive (){ call Leds.redOn(); }
call Send(); // sends something
StdControl.start () {
[....]
for (i=0;i<5000000;i++) ;
}
Now A sends a message while B is running a FOR cycle (make sure that A
sends its message while B is running the for cycle)
You should see that red Led doesn't turn on, because the Receive event
seems to be "LOST".
Andrea
Terence Joseph wrote:
Hi All,
I am using the Tmote Sky. Assume Node A is sending a value to Node B
who upon receipt of this message resends some other value back to node
A straight away. Is there any problems that might occur in this
scenario? For example is it possible that node A may not have time to
switch to receive mode after it has sent its message and therefore
miss the message from Node B? The reason I ask is I have a similar
setup and Node A doesn't appear to be receiving anything at all but is
sending. Any ideas on a solution?
Best Regards,
Terence
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