Broadcom BCM5722 - Figure 28: Overview Diagram of RX Flow

Programmer’s Guide BCM5722
10/15/07
Broadcom Corporation
Document 5722-PG101-R RX Data Flow Diagram Page 70
RX DATA FLOW DIAGRAM
The receive data flow can be summarized in Figure 28. 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 28: Overview Diagram of RX Flow
The following steps describe the RX flow sequence.
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 BCM5722 Ethernet controller from the host-
based Receive Producer Ring.
3. The BCM5722 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.
6. The BD used for the received packet is DMAed from the BCM5722 Ethernet controller to one of the receive return rings,
and the Receive Return Ring Producer Index register in the host status block is updated by the BCM5722 Ethernet
controller.
BCM570X
Family
Rcv BD Std Producer Ring Index
Rcv BD Mini Producer Ring Index
Rcv BD Jumbo Producer Ring Index
MailBox Registers
status word
rcv std cons
unused
rcv jbo cons
unused rcv min cons
Status Block
Standard, Mini, 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 1-16 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