Descriptor Rings
BCM5718 Programmer’s Guide
Broadcom
®
January 29, 2016 • 5718-PG108-R
Page 75
Send Buffer Descriptors
Standard (Not Large Segment Offload)
The format of an individual send buffer descriptor is shown in
The fields are defined as follows:
• The Host Address field contains the 64-bit host address of the buffer that the descriptor points to. A length
of 0 indicates that the descriptor does not have a buffer associated with it.
• The Flags field contains bits flags that contain control information for the device for transmitting the
packets. The defined flags are listed in
.
Table 8: Send Buffer Descriptors Format
Offset (Bytes) 31
16 15
0
0x00
Host Address [63:0]
0x04
0x08
Length [15:0]
Flags [15:0]
0x0c
Reserved
VLAN Tag
Table 9: Defined Flags for Send Buffer Descriptors
Bits
Name
Description
0
TCP_UDP_CKSUM
a
If set to 1, the controller replaces the TCP/UDP checksum field of TCP/UDP
packets with the hardware calculated TCP/UDP checksum for the packet
associated with this descriptor.
1
IP_CKSUM
If set to 1, the controller replaces the IPv4 checksum field of TCP/UDP packets
over IPv4 with the hardware calculated IPv4 checksum for the packet associated
with this descriptor. This bit should only be set in the descriptor that points to the
buffer containing the IPv4 header. It is assumed that the IPv4 header is
contained in a single buffer.
2
PACKET_END
If set to 1, the packet ends with the data in the buffer pointed to by this descriptor.
3
Jumbo Frame
The 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.
4
HDRLEN[2]
The length of the Ether+IP+TCP Headers to be replicated in each segment
arising out of a Large TCP Segment (LSO).
5
Capture Time Stamp (BCM5719/5720 only) If this bit is 1, this frame’s launch time shall be captured
in the TX Time-Stamp Register.
6
VLAN_TAG
a
If set to 1, the device inserts an IEEE 802.1Q VLAN tag into the packet. The 16-
bit TCI (Tag Control Information) field of four byte VLAN tag comes from the
VLAN Tag field in the descriptor.
7
COAL_NOW
If set to 1, the device immediately updates the Send Consumer Index after the
buffer associated with this descriptor has been transferred via DMA to NIC
memory from host memory. An interrupt may or may not be generated according
to the state of the interrupt avoidance mechanisms. If this bit is set to 0, then the
Consumer Index is only updated as soon as one of the host interrupt coalescing
conditions has been met.