Transmit Time Stamping Service; Table 45: Send Ring Sbd Flags - Broadcom NetXtreme/NetLink BCM5718 Series Programmer's Manual

BCM5718 Programmer's Guide

Transmit Time Stamping Service

The software is able to mark certain types of PTP packets (Delay Request, Synch etc) and the NIC hardware
captures the time when such a packet's first byte, or SOF, is launched for transmission. Ideally, the time capture
is the instant of the actual SOF launch on the wire, but due to practical limitations, the capture will take place at
the time the SOF appears on GMII interface among EMAC and GPHY. The propagation delay through the GPHY
is virtually fixed, and hence, could easily be accounted for by system software.The captured time is in reference
to the EAV Reference Count. There is only a single 64-bit register, the TX Time Stamp Register, for this purpose.
The precision of this stamp is 1ns. System software may read the value of this register anytime to get the time-
stamp of last sent PTP packet. Reference the following table of send ring SBD for IEEE1588.
Bit # Flag Name
0 TCP/UDP Checksum Offload Enable This bit enables calculation of TCP or UDP checksums for IPv4
1 IP Checksum Offload enable
2 Packet End
3 Jumbo Frame
4 HDRLEN[2]
5 Capture Time Stamp
6 VLAN TAG
Broadcom
®
January 29, 2016 • 5718-PG108-R

Table 45: Send Ring SBD Flags

Flag Description
and IPv6 transmitted packets. The driver will set this bit only if the
packet contained within a buffer is TCP or UDP over IPv4 or IPv6.
This bit enables calculation of the IPv4 layer-3 checksum. This bit
will be set only for IPv4 packets. The driver will never be set for
IPv6 packets.
This bit will be set for the last send buffer in a packet.
Driver must set this bit to 1 if the MTU length of the Send Frame is
> 1500B. The MTU length is the Ethernet payload length and
excludes Header length (and Trailer length). All BDs belonging to
a Send Packet must configure this bit identically.
The length of the Ether+IP+TCP Headers to be replicated in each
segment arising out of a Large TCP Segment (LSO).
If this bit is 1, this frame's launch time shall be captured in the TX
Time-Stamp Register.
When this bit is set, the NIC will insert a VLAN tag in the Ethernet
header. The value for the inserted tag is taken from the VLAN Tag
field in the send BD.
Transmit Time Stamping Service
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