RX Data Flow DiagramBCM5718 Programmer’s Guide
Broadcom®
January 29, 2016 • 5718-PG108-R Page 100
RX Data Flow Diagram
The receive data flow can be summarized in Figure 17. The Receive Producer Ring, Receive Buffer Descriptors,
Receive Return Rings, Mailbox registers, and status block registers are the main areas of the receive data flow.
Figure 17: Overview Diagram of RX Flow
The RX flow sequence is as follows:
1. The host software updates a Receive Producer Ring Index in the Mailbox registers.
2. A receive BD or series of BDs with the corresponding index is DMAed to the Ethernet controller from the
host-based Receive Producer Ring.
3. The Ethernet controller updates the Receive Consumer Index in the Host Block register and stores copy of
the BD.
4. A valid Ethernet packet is received from the network into the device.
5. The Ethernet packet is DMAed to host memory using a BD previously DMAed from a Receive Producer
Ring.
MailBox Registers
status word
rcv std cons
unused
unused
unused unused
Status Block
Standard and Jumbo Producer Rings
In Host Memory
BD n
Buffer Descriptor points
to free RX buffer in host
TX cons #1 RX prod #1
Receive Return Rings in
host memory
BD n
Used Buffer Descriptor points to host
memory where packet was copied
1
2
3
4
6
5
Host Memory
Network
Rcv BD Std Producer Ring Index
BCM570X
Family
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