Jumbo Frames
BCM5718 Programmer’s Guide
Broadcom
®
January 29, 2016 • 5718-PG108-R
Page 117
• The jumbo producer ring is populated with BDs of a format known as the Extended Buffer descriptors. This
is different from the standard buffer descriptor format.
• It is important to note that the driver may post extended BDs only in the jumbo producer ring and may post
standard BDs only in the standard producer ring. BD formats may not be interchanged.
• The return rings are heterogeneous. That is, the controller returns both standard BDs and extended BDs in
the same return ring. Intermixing of both types of BDs can happen without any restriction.
• RX MBUF memory has been upsized to at least 32 KB.
• Both 4-tuple and 2-tuple RSS computation and classification are performed over RX jumbo frames.
• There are 4 return rings as per RSS requirements (this is not affected by jumbo frame support).
• Receive CRC calculation and checking is performed on jumbo frames.
• Hardware calculates TCP, UDP, and IP checksums on jumbo frames.
• In IOV mode (I/O Virtualization), all 17 receive queues (virtual receive queues) must be provided with
extended receive BDs. To that end, each VRQ is provided with a dedicated standard receive BD (RBD) ring
and a dedicated jumbo RBD Ring.
Other:
• Miscellaneous BD memory has been increased over legacy NetXtreme controllers from 6K (4K receive BD
+ 1K send BD + 1K gencomm) to 51 KB (17 KB standard receive BD + 17K jumbo receive BD + 16 KB
send BD + 1K gencomm). Gencomm describes on-chip memory space used for driver to/from boot code/
firmware communication.
• The structure of the status block has been updated in order to accommodate jumbo frame related
information.
• The controllers memory map has also been updated.
Affected Data Structures
The data structures introduced, updated, or affected due to jumbo frame support are discussed in this section.
In IOV mode, some of these structures are instantiated 17 times in case of receive and 16 times in case of
transmit.
Extended RX Buffer Descriptor (BD)
The extended buffer descriptors are only permitted to be posted to the jumbo producer ring. The structure is
shown in
Figure 23: “Extended RX Buffer Descriptor,” on page 118
. The main distinction of the extended BD
structure is that it can point to a maximum of four pieces of a scattered receive buffer. Hence the structure
contains four host addresses and four length fields.