Figure 23: Receive Return Ring Memory Architecture Diagram - Broadcom BCM5722 Programmer's Manual

Programmer's Guide
10/15/07
Host Memory
Host Buffer
1-(64K-1) Bytes
Status Block (80 bytes)
Status block resides in the NIC memory
space and is periodically DMA'd to the
host based on the host coalescing
timer.
Document 5722-PG101-R
Receive Buffer Descriptor
Host
Address
index len
type flags
ip chksum tcp_udp_chsum
error flag vlan tag
reserve
d
opaque
RX BD
Status Block
Status Word
unused
RX std cons RX big Cons
Unused RX mini Cons
TX Cons #1 RX Prod #1
RX Prod #2
TX Cons #16 RX Prod #16
The NIC is the Producer of the receive
return ring. It increments the internal
producer index to add elements to the ring .

Figure 23: Receive Return Ring Memory Architecture Diagram

B roa dcom Cor po rat ion
Receive Ring #1
Prod
1st
RCB #1
Cons
Receive Ring #16
Prod 1st
Con Mailbox Registers
Ring Control Block
Host Ring Address
max_len flags
NIC Ring Address
The ring and gives the length of the ring.
and configures the ring. The NIC ring
address is invalid for the receive return ring
RCB #16
RX Cons #1
RX Cons #2
RX Cons #16
Note:
The receiver return rings are always
stored in host memory.
BCM5722
Page 48