tcpdump mailing list archives
Re: Fwd: Re: Printing nanosecond timestamp information in raw output
From: Maik Jäkel <email () maikjaekel de>
Date: Sat, 29 Dec 2012 12:44:38 +0100 (CET)
@Guy: Once again thanks for your detailed answer. I'll try to modify pcap then. @James and Rixed: I just ran a test on my device. The test takes 150 timestamps and calculates the difference between of every timestamp and the timestamp taken after it. My device is a little older. Its cpu only runs at 800MHz and is a single core cpu. That output looks pretty good to me, even though there is a zero diff here and there. I also ran the test in an infinity loop while putting the cpu under a stress test. The results are the same. The values are either 30517,30518 or 0ns. This is my loop code (res is a timespec struct): for(i = 0; i < 150; i++){ clock_gettime(CLOCK_REALTIME, &res); secDiff = res.tv_sec - oldSec; nsecDiff = 1000000000 * secDiff + res.tv_nsec - oldNSec; oldSec = res.tv_sec; oldNSec = res.tv_nsec; printf("Diff: %ldns\n", nsecDiff); } This is the output: Diff: 30518ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 0ns Diff: 30517ns Diff: 30518ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30518ns Diff: 30517ns Diff: 0ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 0ns Diff: 30517ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30518ns Diff: 30517ns Diff: 30518ns Diff: 30517ns Diff: 30518ns ----- Ursprüngliche Mail ----- Von: rixed () happyleptic org An: tcpdump-workers () lists tcpdump org CC: "Maik Jäkel" <email () maikjaekel de> Gesendet: Samstag, 29. Dezember 2012 10:15:51 Betreff: Re: [tcpdump-workers] Fwd: Re: Printing nanosecond timestamp information in raw output
I didn't know a better way, though and hoped that the execution time between the reception of the packet and taking the timestamp is relatively constant (with an uncertainty of 4ns or so).
On a 1.2GHz cpu clock, as is typical of android devices these days, that would be 5 clock ticks, ie 5 ARM instructions at best. I'd be very surprised if the uncertainty for such a long periple from reception to timestamping were that low. Please keep the list informed when you have measured the actual variation between timestamps of outgoing packets. _______________________________________________ tcpdump-workers mailing list tcpdump-workers () lists tcpdump org https://lists.sandelman.ca/mailman/listinfo/tcpdump-workers
Current thread:
- Fwd: Re: Printing nanosecond timestamp information in raw output Maik Jäkel (Dec 28)
- Re: Fwd: Re: Printing nanosecond timestamp information in raw output Guy Harris (Dec 28)
- Re: Fwd: Re: Printing nanosecond timestamp information in raw output Guy Harris (Dec 28)
- Re: Fwd: Re: Printing nanosecond timestamp information in raw output Maik Jäkel (Dec 29)
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- Re: Fwd: Re: Printing nanosecond timestamp information in raw output Maik Jäkel (Dec 29)
- Re: Fwd: Re: Printing nanosecond timestamp information in raw output Guy Harris (Dec 28)