Re: Problem with frame time stamping

From: Eric Dumazet
Date: Tue Nov 13 2007 - 05:36:51 EST

Antoine Zen-Ruffinen a écrit :
What does it bring me to have a nanosecond precision if it is not
related to the actual arrival of frame time ? As it seem I can feel
skb->tstamp with whatever I want, I always become something else using
ioctl(). (I'm using kernel 2.6.23).

2007/11/12, Eric Dumazet <dada1@xxxxxxxxxxxxx>:
On Mon, 12 Nov 2007 16:42:34 +0100
"Antoine Zen-Ruffinen" <antoine.zen@xxxxxxxxx> wrote:

Dear all,

I'm writing a network analyzer software using Linux and I need a VERY
precise frame time stamping. Therefor I am planing to add my own time
stamping algorithm on a modified network driver. For test purpose I
did so :

skb->tstamp.tv64 = 0x00010002;

On the user side, I ask for the timestamp that way :

sock = socket(AF_PACKET, SOCK_RAW, type);
//bind this socket with the interface using my modified driver.
recvByteCount = recv(sock, buffer, 1514, 0);
ioctl(sock, SIOCGSTAMP, &timeStamp);

I was surprised to see that the var timeStamp was still holding a
count of second since year 1970.
But then, maybe your problem comes from your code : timeStamp should be declared as "struct timeval" of course, to get both tv_sec and tv_usec.

struct timeval tv;
ioctl(sock, SIOCSTAMP, &tv);
printf("packet arrived at %ld.%06ld\n", (long)tv.tv_sec, (long)tv.tv_usec);

If you *want* nanosecond resolution instead of microsecond, use :

struct timespec ts;
ioctl(sock, SIOCSTAMPNS, &ts);
printf("packet arrived at %ld.%09ld\n", (long)ts.tv_sec, (long)ts.tv_nsec);

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