We are using a DP83848K to transmit in 100BaseT Full Duplex mode and are seeing a significant delay between when the TX_EN pin is active and when we see the packet on the wire with wireshark.
Our application transmits 1 packet every 65ms and we have a scope on the TX_EN pin as input to the DP83848K. The TX_EN pin triggers as expected every 65ms with some jitter on the order of a few microseconds at most, but our packet timing as seen on wireshark can vary by a few milliseconds.
If we run for a hour or so, we usually have up to about 10 packets that seem to have been delayed for a few milliseconds. And all that time no variation to speak of in the input signals to the DP83848K.
I am wondering if anyone else has experienced this issue.
We are in the process of getting a scope that will decode ethernet packets so I can see the timing of both events on a single time source and not rely on wireshark for packet timing, but I don't think this is the source of the problem.
There is no switch in between our transmitting connector. Only about a 10ft long ethernet cable to the laptop running wireshark.
Any help is much appreciated.
Eric