Ethernet AVB Endpoint - 9.0 English

Tri-Mode Ethernet MAC LogiCORE IP Product Guide (PG051)

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9.0 English

This section provides information about the key functional blocks which are introduced when the optional AVB Endpoint is included in the core.

Important: It is actually the “controlled frequency RTC” nanoseconds field which is sampled by the timestamping logic rather than the synchronized RTC (see Figure 1 ). This is important when operating as a clock slave: the controlled frequency RTC always acts as a smooth counter and the synchronized RTC might suffer from occasional step changes (whenever a new offset adjustment is periodically applied by the software drivers). These step changes are avoided by using the controlled frequency RTC, could otherwise lead to errors in the various PTP calculations which are performed by the software drivers.
Tip: The software drivers can themselves obtain (when required) the local synchronized RTC value by summing the captured timestamp with the current nanoseconds offset value of the RTC Nanoseconds Field Offset Control (effectively performing the step 2 calculation of Figure 1 in software).