5.2.5.1 Timestamping - Frame Egress

Transmit timestamping is enabled by setting the Frame Timestamp Enable (FTSE) bit in the Configuration 0 (OA_CONFIG0) register. The SPI host will indicate to the LAN8650/1 that a transmit (egress) timestamp should be captured for a specific frame by writing the Timestamp Capture (TSC) field of the transmit data header. The TSC field is only valid in the corresponding data header of the transmit data block payload containing the beginning of a new frame, i.e., Start Valid (SV) is set to ‘1’. A non-zero TSC field indicates which of three Transmit Timestamp Capture High/Low registers (TTSCAH/L, TTSCBH/L, TTSCCH/L) the captured egress timestamp value for the frame will be placed. When the frame is transmitted, the LAN8650/1 will capture the current timestamp, place the timestamp into the desired Transmit Timestamp Capture register pair, and set the appropriate Transmit Timestamp Capture Available (TTSCAA, TTSCAB, TTSCAC ) status bit in the Status 0 (OA_STATUS0) register. If enabled, the IRQ_N pin will also be asserted.

When the TSC header field is zero (or frame timestamping is disabled), no frame egress timestamp will be captured.