Programmer’s Guide BCM5722
10/15/07
Broadcom Corporation
Document 5722-PG101-R Receive Data Path Page 16
RULES CHECKER
The rules checker examines frames. After a frame has been examined, the appropriate classification bits are set in the buffer
descriptor. The rules checker is part of the RX data path and the frames are classified during data movement to NIC memory.
The following frame positions may be established by the rules checker:
• IP Header Start Pointer
• TCP/UDP Header Start Pointer
• Data Start Pointer
RX LIST PLACEMENT
The RX List Placement function determines one of the multiple receive lists the frame should be placed on. Then, the RX
List Placement block adds the frame to the appropriate list. The selection is based on a class value in the frame descriptor.
There are no configuration registers for this block beyond the mode control register (see “Mode Control Register (Offset
0x6800)” on page 333). The BCM5787, BCM5787M, BCM5906, BCM5906M, BCM5754, and BCM5754M devices have only
one receive list; hence, all the received frames not discarded by the rules checker are placed into one receive list. The
BCM5755 and BCM5755M devices support four receive lists.
RX LIST INITIATOR
The RX List Initiator function activates whenever the receive producer index for any of receive buffer descriptor (BD) rings
is written. This value is located in one of the receive BD producer mailboxes. The host software writes to the producer
mailbox and causes the RX Initiator function to enqueue an internal data structure/request, which initiates the DMA of one
or more new BDs to the NIC. The actual DMAs generated depend on the comparison of the value of the received BD host
producer index mailbox, the NIC’s copy of the received BD consumer index, and the local copy of the received BD producer
index.
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