[Tinyos-help] FTSP Question

[Michael Schippling]

I found that the Boomerang time-sync code had an arbitrarily low threshold
for correcting clock drift due to differing timer crystals. There may be
something similar in FTSP.

MS

Scott Moeller wrote:
> I'm using packet source and sink timestamps from FTSP to carry out a 
> performance evaluation of my work.  I'm having trouble with FTSP, 
> however, and am hoping somebody might have suggestions.
> 
> Hardware:
> I'm using tmote sky devices (4 of them), so we are dealing with the 
> CC2420 Radio.
> 
> TinyOS:
> I'm running TinyOS 2.1
> 
> Test 1:
> 1) I install my code (which uses FTSP) on the four motes, one at a time 
> - this ensures that local timers are started many seconds apart.
> 2) I let FTSP run alone for one or two minutes, though I've tested as 
> long as 10 minutes.
> 3) I send a serial command to begin traffic flow from 3 sources to 1 
> sink mote.
> 4) FTSP Timestamps indicate ~10 milliseconds / hop latency - this is good.
> 5) Repeatedly over 10 minutes of traffic logging, FTSP timestamps on 
> several nodes "jump" back in time more than ten seconds.
> 6) Occassionaly mid traffic the getGlobalTime() call returns ERROR 
> status, indicating lack of sync.
> 
> So I know FTSP is working, but once my traffic starts up I periodically 
> get synchronization issues.  I am working in a wirelessly "crowded" lab 
> [though we have assigned channels to users], so it is possible that 
> somebody else is using FTSP on my channel.  I've therefore run tests on 
> both channels allocated to my group.
> 
> The following has been my temporary work-around, but it's not desirable.
> 
> Test 2:
> 1) I install my code on the four motes.
> 2) I wait 2-5+ minutes, then send a serial command to switch FTSP into 
> TS_USER_MODE.  This stops automated FTSP broadcasts.
> 3) I send a serial start command to begin my traffic flow.
> 4) Timestamps are clean, I don't see large jumps in values.  However, I 
> can see slow drift between some sources and the sink (packet times drop 
> from 10ms / packet to under 5ms over a 20 minute log period).
> 
> This is better, but clock drift is untidy, I shouldn't have to disable 
> FTSP activities to get clean timestamps....
> 
> I've read the FTSP wiki page:
> http://docs.tinyos.net/index.php/FTSP
> 
> They mention a CC2420 timestamp bug in Tinyos 2:
> http://docs.tinyos.net/index.php/PacketTimeStamp_CC2420_bug
> 
>  Am I a victim?
> 
> Thanks,
> 
> -Scott Moeller
> ANRG Research Group
> USC
> 
> 
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> 
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-- 
Platform: WinXP/Cygwin
TinyOS version: 1.x, Boomerang
Programmer: MIB510
Device(s): Mica2, MicaZ, Tmote
Sensor board: homebrew