Hi Terence,
You mentioned something important. How do i get to prioritise the operation. In other words, i measure the time of Receipt immediately on Receipt of the RF message. This is what the sender and receiver are doing:
Sender: MOTEA
if (call DataMsg.send(TOS_BCAST_ADDR, sizeof(RFMsg), &data))
{
pending=TRUE;
TOSH_SET_CNT_PIN(); //PB5=1 This Pin is directly connected to the B to signal timer start
TOSH_uwait(7);
TOSH_CLR_CNT_PIN(); //PB5=0;
}
.....
Receiver: MOTEB
TOSH_SIGNAL(SIG_INTERRUPT5) { //PB5 connected here - When rising edge - start timer3
....
sbi(TCCR3B, CS32);
sbi(TCCR3B, CS30);
}
event TOS_MsgPtr RadioReceive.receive(TOS_MsgPtr Msg) { // Read Timer3 and reset
timebtween=__inw_atomic(TCNT3L);
// Print timebtween ......
outp(0,TCNT3L);
cbi(TCCR3B, CS32);
cbi(TCCR3B, CS30);
return Msg;
}
I then have timebtween giving me values quite close at certain times and far apart at different times, which i understand comes from internal message buffering.
Where could the prioritising take place? Also, is there any Tinyos component that just pings motes?
Thanks
From: "Terence Joseph" <[EMAIL PROTECTED]>
To: [email protected]
CC: [EMAIL PROTECTED]
Subject: RE: [Tinyos-help] Time of Flight of Messages between two Motes
Date: Wed, 23 Nov 2005 15:30:56 +0000
>I would say the delay you see here has to do more with the
>processing going on on each node than the time of flight for each
>message which at 60cm would only take about 2ns although you're
>probably aware of this. I would also say that if you are using a
>timer the sending time will be fairly constant so its really and
>issue with the receiver. From the time a receive event is triggered
>until the time you actually see the data (i.e. the time it will take
>the data to be passed to the MPU and out to the USB port) is where
>the delay is occuring I would think (however this is assuming you
>are measuring the receive time at this point which you haven't
>specified). If you want it fairly constant you would therefore need
>to prioritise this operation somehow although I doubt you could get
>it 100% constant. I could be wrong with all this of course but
>they're just my thoughts.
>
>Regards,
>Terence
>
>
>Hi all,
>
>I would like to know, if i can have an approximately constant time
>of flight of an RF message between two motes. When i place two motes
>about 60cm apart and send messages every 2 seconds, i discover that
>it takes about 2.9 ms to leave from A to B, and later on it takes
>about 6.4 ms between the same route. Does anyone know how, i can get
>a mote to send at a constant rate(or rate where the times dont
>differ too much), or is this impossible?
>
>Thanks
>
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