IOV – Transmit SideBCM5718 Programmer’s Guide
Broadcom®
January 29, 2016 • 5718-PG108-R Page 268
• Only Host based Rings supported (NIC based Rings defeatured early on)
• Maximum Ring size of 512 each
• 16 High Priority Send Producer Index Mailboxes – one per ring
• 16 Send Ring Control Blocks (RCB)
• 1KB of private on-chip SBD cache per Ring – Total 16KB
• Introduction of a SBD Fetch Threshold
• Send BD Format unchanged in Multi Ring mode.
• No Rate / Traffic Shaping algorithm offered
• Very basic round-robin packet by packet arbitration among 16 Send Rings
• All Send Offload features, namely LSO & Checksum-Offload shall continue to function in all rings without
any behavior change.
• Minimal set of per Send Queue EMAC Statistics
The basic Send interface with the Device Driver remains unchanged, only the number of Send Rings are scaled
up to 16 from 1. Thus there shall be 16x Send Producer BD Index Mailboxes and 16x Ring Control Block
Registers in controller.
SBDs are fetched from the Host memory and are stored in SBD-cache memory internal to the chip. Though such
a cache memory could be shared by all 16 Rings, for the sake of simplicity we chose to assign each Send Ring
a private partition of the SBD cache – physically it is a single SRAM, but is divided into 16 equal address regions.
Each such address range shall serve as a private SBD cache to a Send Ring. The total size of the SBD cache
is thus 16 KB.
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