Add Timestamping to socketcan_interface

[Worldman2]

There should be a way to obtain the timestamp of receiption for a CAN-frame. Ideally, this should be the HW-timestamp, if the device supports it (using SIOCSHWTSTAMP). According to the socketcan documentation, timestamps can be obtained by an ioctl-call after reading a message from the socket.

I tried hacking something into socketcan.h but failed. My approach was to just add

ioctl(socket_.native_handle(), SIOCGSTAMP, &tv);

at the beginning of SocketCANInterface::readFrame(...) and

setsockopt(sc, SOL_SOCKET, SO_TIMESTAMP, &timestamp_on, sizeof(timestamp_on));

in the init(...) method. However, the values seem wrong (inconsistent, jumping, in the range of 10^12). So it probably just proves how few I understand about socketcan and boost::asio.

Is there a possibility for a recent implementation of this feature request or could you provide some hints how to realize this? Thanks!

[mathias-luedtke]

I tried it myself some time ago, but for some reason I did not include it somewhere. If I remember it correctly, not all devices set these time stamps and in addition it is unclear what time base they use.

However, timestamps would be a nice feature!

ioctl(socket_.native_handle(), SIOCGSTAMP, &tv);

This looks right, not sure why it is delayed.

[Worldman2]

As far as I understand, even if the hardware does not support it, there is at least the option to retrieve the socket timestamp (SO_TIMESTAMP) of the last received packet. I think, this is also what candump does: https://github.com/linux-can/can-utils/blob/master/candump.c#L676

[mathias-luedtke]

Found my implementation again: https://github.com/ipa-mdl/ros_canopen/tree/stamped_data However, this does not use CAN-based timestamps.

[ozzdemir]

This source mentions the following. It might the reason for the inconsistent timestamp.

Note that SIOCGSTAMP and SO_TIMESTAMP are mutually exclusive - if you're going to use SIOCGSTAMP you should disable SO_TIMESTAMP (with enabled = 0). This is because SO_TIMESTAMP directs the kernel to make the timestamp available via recvmmsg ancillary data instead of via SIOCGSTAMP.