Dear all,
I have been working on a time sync protocol between the pc and the
motes. I think I have solved most of the problems on the java side and I
would like to improve things on the motes.
My test for the time-sync consists of running the sync protocol every
i.e. 60 seconds and sending messages to 2 motes every 2 seconds which
say: "at time X, change the DAC". I use a digital oscilloscope to
monitor the outputs and see how good the response is (difference between
both responses). As for now, I have noticed that for each resync the
delay in the changes of the DAC outputs remains constant, but there are
great differences between two resyncs: one might give a difference of
1ms and the next a difference of 20ms. I am trying to reduce this
variability as much as possible
As Janos suggested, I have looked for a way to do the timestamping with
the SFD interrupt. Looking through CC2420RadioM, I have noticed
async event result_t SFD.captured(uint16_t time).
Looks like there is a timestamping going on already, and I have read
somewhere that it is recorded on rxbufptr->time, so I've been trying to
extract it on message reception (In ReceiveMsg.receive) like this:
event TOS_MsgPtr ReceiveMsg.receive( TOS_MsgPtr msg ) {
struct TOS_Msg* r_time;
r_time = (struct TOS_Msg *)msg->data;
t2 = (r_time->time)/0.032;
}
But it doesn't seem to be working. I get three or four fixed values every time
a synchronisation is run (0 and 10013) come to mind...
I have tried vu's timestamping as well but on a call to get timestamp t2 is
always
0. Does anyone know a simple way to get a timestamping with the SFD interrupt
handler?
Or a suggestion as to to why a resynchronisation has such a big variability
while the delays
are so constant (which would suggest that the problem is not on the timers, but
on the send/receive
interfaces) and how to improve it?
Any comments are appreciated.
Thank you,
- Jose.
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