Send RingsBCM5718 Programmer’s Guide
Broadcom®
January 29, 2016 • 5718-PG108-R Page 107
Ring Control Block
The Send Ring RCB contains a pointer to the first Send BD in the device and host memory, number of send BDs
in the ring, and control flags (see “Send Rings” on page 105 for a full discussion of the send RCB). All the fields
are in big-endian ordering as required by the Ethernet controller. The RCBs of the send rings are located in the
device Miscellaneous Memory Region at offset 0x0100.
The devices support a host based send ring. The Send BDs of the host based Send Ring will be bus-mastered
from host memory into device local memory. The device driver will program the BDs directly in its memory space
and avoid programmed I/O to the MAC. The Max_Len field in the RCB (see Figure 20) indicates the maximum
number of BDs in the Send Ring. This field can be programmed to either 32, 64, 128, 256, 512, 1024, 2048, or
4096, depending on the type of ring for which the corresponding RCB applies.
Figure 20: Max_Len Field in Ring Control Block
Offset 32 16 15 0
Host Ring Address
0x00
0x04
Flags0x08
0x0C NIC Ring Address
Max_Len
Host Send Ring Control Block
1st
1st Ring Element 512th Ring Element
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