[Tinyos-help] telosb: Send.send() to SFD latency

Giang Nguyen cauthu at gmail.com
Thu Sep 29 12:24:10 PDT 2005


hi,
i am on telosb motes.
it takes some time T from when Send.send() is called until the packet is in
the air (which i take to be when the SFD is captured and consequently
RadioSendCoordinator.startSymbol(8, 0, txbufptr) is signaled).

GOAL: i'm trying to keep T as close to a constant as possible.

_all of the following comments are in the case of no/little congestion (ie,
there's only 1 mote sending)_

T depends on the random initial backoff:
(using the 32khz clock)
min T: 63 ticks
max T: ~500 ticks
avg T: ~155 ticks

so, to achieve the GOAL, i need to know the (random) initial backoff
interval in advance (ie before calling Send.send()).

so i changed MacBackoff.initialBackoff() to return a constant, say, 10,
instead of the current random return value. then, the avg (~155) is very
close to the min (~153).

QUESTION: is there a better way to achieve the GOAL (at least in the case of
no/little congestion)?

thanks.
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