Section 8: Ieee1588; Ieee1588 Time Sync Introduction; Netxtreme Time Sync Assist; Coexistence - Broadcom NetXtreme/NetLink BCM5718 Series Programmer's Manual

BCM5718 Programmer's Guide

IEEE1588 Time Sync Introduction

IEEE1588 and IEEE802.1AS are two protocols designed to perform time synchronization over Ethernet
networks. IEEE1588 Precision Time Protocol (PTP) provides a UDP packet based time synchronization
mechanism, while IEEE802.1AS extends PTP to operate directly over the L2 or Ethernet layer. Time precision
offered by PTP is in the sub-microsecond range and, in fact, can get down to a Nanosecond.

NetXtreme Time Sync Assist

NetXtreme architecture provides a set of hardware (HW) features to assist IEEE1588 and IEEE802.1AS traffic
over Ethernet. Both 1588 and 802.1AS are complex protocols from the perspective of statefulness and are best
implemented by a software module resident in the host computer. However, since these protocols demand a
sub-microsecond, in some cases nanosecond grade precision, long latencies encountered by host software do
not permit these protocols to be implemented in software (Host CPU) in their entirety. The goal of NetXtreme
architecture is to provide the cheapest and simplest set of HW hooks so that a service grade PTP profile may
be enabled in the host server computer.
The assists that NetXtreme provides are:
• A 64-bit Counter clocked by the 125 MHz DLL clock to serve as the Precision Clock – Thus 8ns is the
maximum precision offered. This clock is known as the EAV Reference Clock.
• A 64-bit Transmit Time Stamp Register – Software shall mark certain types of PTP message Packets in turn
for TX hardware to capture launch time of that packet.
• A 64-bit Receive Time Stamp Register – RX hardware shall crack and identify certain types of PTP packets
as configured by host SW. The reception time of such a packet shall be recorded in this register. Host SW
shall retain the control to choose which PTP message Types get time stamped.
This feature, Time Sync Assist, may be enabled by setting a Mode bit in the chip.

Coexistence

The Time Sync Assist feature coexists with the following NetXtreme features:
• VLAN Tagging – In-band or out-of-band
• SNAP/LLC Framing – Transmit and receive.
• Transmit LSO – Note that PTP packets cannot be TCP segments.
• Transmit IP, UDP, TCP checksum offload – IP/UDP Transmit Checksum offload is applicable to UDP PTP
packets, provided the packets are appropriately formatted by the software protocol engine, that is, 2B UDP
padding etc must be taken care by software.
Broadcom
®
January 29, 2016 • 5718-PG108-R
S e c t i o n 8 : I E E E 1 5 8 8
IEEE1588
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