The diagram above shows the point in the TX datapath where the two-step operation is performed. The time stamp references are defined as follows:
- TS2: The output timestamp signal when a two-step operation is selected.
- TS2': The plane to which both timestamps are corrected.
TS2 has a correction applied so that it is referenced to
the TS2' plane, depending on the value of the signal
ctl_tx_ptp_latency_adjust[15:0].
On the transmit side, a command field is provided by the client to the subsystem in parallel with the frame sent for transmission. This indicates, on a frame-by-frame basis, the 1588 function to perform (either no-operation or two-step). If using the ToD format, then for both one-step and two-step operation, the full captured 80-bit ToD timestamp is returned to the client logic using the additional ports defined in Port Descriptions. If using the Correction Field format, then for both one-step and two-step operation, the full captured 64-bit timestamp is returned to the client logic using the additional ports defined in Port Descriptions (with the upper bits of data set to zero as defined in the table).