We are using two ports of a i350-T2 NIC to do some network testing. We are capturing broadcast/multicast packets on both ports and doing some processing using the timestamp information. To dump the packets we are using tcpdump with the "-j adapter_unsynced" argument on both ports of the NIC; which should be using the NIC's unadjusted timestamps to timestamp each packet.
The problems is that the timestamps between between the two ports on the same i350 NIC have large offsets, 36000.xxx seconds, which suggests that a separate counter is used to timestamp each port. It is not clear from reading the datasheet if this is the case.
So are separate hardware counters used to timestamp each port? If so, is there a way to synchronously reset or read the counter values to deal with this offset?