5.2.5 Ethernet Frame Timestamping

The LAN8650/1 supports timestamping on egress (transmit) or ingress (receive) of Ethernet frames via the MDI. The Frame Timestamp Capability (FTSC) bit in the Standard Capabilities (OA_STDCAP) register indicates that the LAN8650/1 supports frame timestamping. Frame timestamping is enabled by setting the Frame Timestamp Enable (FTSE) bit within the Configuration 0 (OA_CONFIG0) register.

Both 32‑bit and 64‑bit timestamp formats are supported, as shown in Figure 5-3 and Figure 5-4. Each timestamp format contains a 30-bit nanoseconds field which rolls over each second to zero at 0x3B9ACA00. The seconds field is incremented by one each time the nanoseconds field rolls over. The 32‑bit timestamp contains a 2‑bit seconds field allowing for a range of 4 seconds. The 64‑bit timestamp includes a larger 32‑bit seconds field.

Figure 5-3. 32-bit Timestamp Format
Figure 5-4. 64-bit Timestamp Format

The time stamp is captured by the MAC Time Stamp Unit; time stamps will be captured at the end of the Start-of-Frame delimiter for both inbound and outbound frames.