Re: Flexcan - timestamp from message buffer to userspace

[Oliver Hartkopp <socketcan@hartkopp.net>]

On 18.10.2013 12:55, Martin Kozusky wrote:
> 
> Dne 18.10.2013 11:56, Martin Kozusky napsal(a):
>> Hello,
>> is there any official way how to read timestamp from flexcans message
>> buffer?
>> I see there is a macro defined FLEXCAN_MB_CNT_TIMESTAMP in flexcan.c,
>> but not used.
>> I would modify function flecan_read_fifo like
>>
>> + u32 timestamp = FLEXCAN_MB_CNT_TIMESTAMP(reg_ctrl);
> 
> sorry, u32 should be just u16
> 
>> but what to do with timestamp variable next and how to read it in
>> userspace? :) I could change structure can_frame and add  u32 timestamp
> also u16, not u32
> 
>> into it, but it wouldn't be very nice hack I think.
>>
>> BTW: is timestamp read with SO_TIMESTAMP  actualy taken when CAN message
>> arrives?
>>

Hello Martin,

with SO_TIMESTAMP you get the system timestamp in nanosec resolution.

It is set at the time when the CAN frame is pushed to the network layer by
the CAN drivers interrupt routine.

See net_timestamp_check() in netif_rx():

http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/net/core/dev.c#n3228

You may get this timestamp via ioctl() or recvmsg().

To pass hardware timestamps there's some infrastructure for ethernet devices in the
mainlaine kernel, which is configured with "ethtool":

   ethtool -T|--show-time-stamping DEVNAME    Show time stamping capabilities

See details at

http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/networking/timestamping.txt

And some example source code at 

http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/networking/timestamping/timestamping.c

There needs to be added some infrastructure to the network devices to query
and configure the timestamping possibilities.

This is currently missing for CAN devices ...

Even if I moved a wrongly assigned hardware timestamp to another place here:

http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/drivers/net/can/usb/peak_usb?id=c9faaa09e2a1335678f09c70a0d0eda095564bab

the rest of the hardware timestamping (& configuration) is still missing.

Regards,
Oliver