[EMAIL PROTECTED] (Martin Burnicki) writes: [...] > 3.) By the NIC hardware. You need a time stamp unit (TSU) which listens on > the > data lines between the MAC and the PHY. The TSU contains a pattern matching > unit which detects the pattern of the desired packet type in the serial bit > stream on those data lines. If such a pattern is detected then the pattern > matching unit must capture a time stamp of a high speed counter which is also > part of the TSU. Since this method takes time stamps when a packet goes on > the wire or arrives on the wire is also capable to eliminate the latency due > to network collisions. > The driver must be able to read those time stamps from the TSU and either > assign them to the packets or pass them up the protocol stack to the > application which then assigns the time stamps to the packets. > The TSU can be implemented in a programmable logic device like an ASIC or > FPGA. > This method is the most accurate, but it requires a NIC with a TSU, and a > kernel driver which supports the TSU. > The problem here is that most commonly used NICs have the MAC and the PHY in > a > single chip, and the data lines on which the TSU must listen is not > accessible outside the chip. > > You must also be aware that the timing accuracy is significantly degraded if > the PTP packets go through switches or routers which don't have a special > handling for such packets, so packets may be queued which introduces again > an
It would be an interesting experiment to echo those PTP packets 1) directly via an X-cable 2) via some switch, hub, etc. [...] Regards, Ulrich Windl _______________________________________________ questions mailing list [email protected] https://lists.ntp.isc.org/mailman/listinfo/questions
