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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