When IEEE 802.1AS is implemented with
PHY level timestamping, the PTP timestamped messages and associated PTP sequence IDs
are stored within the PHY. Accessing these packets using the traditional MDC/MDIO
serial interface can take microseconds to a few milliseconds and is sometimes
complex to integrate with 802.1AS software stack running in the SoC.
To ease the integration with gPTP, TI
PHYs offers additional two ways to provide PTP timestamps to host SOC.
- Appending the timestamp in the PTP message before being forwarded to the ECU
through the RX interface.
- A packet-based status mechanism that allows the PHY to generate in-band
Ethernet frames with timestamps to the SoC. The packet, called a PHY
Status Frame, can be used provide transmit PTP packet timestamps,
receive PTP packet timestamps, event timestamps, and trigger
conditions.
These additional capabilities allow SoC to access the PTP messages directly
from the IEEE 802.1AS software stack as opposed to having to access the messages
through MDIO/MDC, making the integration of gPTP easy and efficient.