Thanks Oliver!

I'm facing an issue with timestamping (not only TX), I hope someone
could help me with that.

The problem is that I don't receive control message with timestamp
from recvmsg(), although SO_TIMESTAMP is enabled.
Here's how I open the socket and read from it: http://pastebin.com/2iQrQuY3
Problem is at line 78 - recvmsg() returns no control messages.

$ uname -a
Linux spym-pc 3.2.0-60-generic #91-Ubuntu SMP Wed Feb 19 03:54:44 UTC
2014 x86_64 x86_64 x86_64 GNU/Linux

What I'm doing wrong?

Thanks in advance,
Pavel.

On Sat, Mar 22, 2014 at 11:22 PM, Oliver Hartkopp
[off-list ref] wrote:

Hello Pavel,

On 20.03.2014 17:28, Pavel Kirienko wrote:

quoted

Hi linux-can,

What are my options to get the hardware TX timestamp of an outgoing
CAN frame? I couldn't find complete manual for that, but here's what I
googled so far:

1. Use generic socket timestamping, as described in the network man
(http://os1a.cs.columbia.edu/lxr/source/Documentation/networking/timestamping.txt?a=x86);

2. Read my own frames back through CAN_RAW_RECV_OWN_MSGS, supposedly
RX timestamps of the loopbacked frames will be the same as their TX
timestamps.

Are these the correct methods?

Yes.

With CAN_RAW_RECV_OWN_MSGS you get the echoed frame on a socket which
originally sent the frame.

The timestamps are currently only set at RX time.

http://os1a.cs.columbia.edu/lxr/source/net/core/dev.c?a=x86#2864
http://os1a.cs.columbia.edu/lxr/source/net/core/dev.c?a=x86#1463

As you can see in net_timestamp_check()

http://os1a.cs.columbia.edu/lxr/source/net/core/dev.c?a=x86#1471

the timestamp is only set if it was empty before.

E.g. if you forward a CAN frame with can-gw there's an extra option to not
clear the timestamp when routing the frame (option -t [preserve src_dev rx
timestamp]).

As the sent frames are echoed back you are pretty right that the RX timestamp
and the TX timestamp are the same.

Regards,
Oliver