PM7375-SC datasheet(93/430 Pages) PMC

93 / 430 page

PM7375 LASAR-155

DATA SHEET

PMC-931127

ISSUE 6

LOCAL ATM SAR & PHYSICAL LAYER

PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE

9.14.8 Receive Packet Queues and Operation

RPDRs pointing to free RPD are passed from the PCI Host to the RRM using the

Receive Packet Descriptor Reference Small Free (RPDRSF) and the Receive

Packet Descriptor Reference Large Free (RPDRLF) Queues. The RRM uses one or

more free RPDs for packet reassembly. Two free queues are used by the RRM, the

RPDRLF Queue for large buffers and the RPDRSF Queue for small buffers. At the

start of packet reception the RRM will use a small buffer to store the start of a

packet. If the packet exceeds the small buffer size, the RRM will use large buffers

to store the remainder of the packet.

In order to take advantage of burst PCI transfers, the RRM reads up to six RPDs

from each Free Queue and stores them locally. Once a packet has been

reassembled, the RRM passes completed RPDs to the PCI Host using the Receive

Packet Descriptor Reference Ready (RPDRR) Queue.

All three Queues reside in PCI Host memory and are defined using a common base

pointer residing in the PCID Receive Queue Base register and twelve offset

pointers, four per queue. For each queue, two pointers are required to define the

start and the end of a queue while two pointers are required for the current write and

read locations within the queue. The read pointer always points to the last location

read while the write pointer always points to the next location to be written.

A full condition for the queues is defined as the read and the write pointers being

equal. A empty condition is defined as the read pointer one less then the write

pointer. The last location in a queue is not considered as part of the queue and thus

is not a valid entry.

The LASAR-155 reassembles packets using RPDs in Host memory. Each RPD

contains control fields, a RPD pointer reference field and a buffer pointer field. The

control fields are used by the LASAR-155 to indicate to the PCI Host which VC a

reassembled packet is associated with and the state of the reassembled packet.

The buffer pointer is used to point to a buffer where the reassembled packet is

stored. If the packet was too large for a single buffer, the RPD pointer reference

field is provided to create a linked list of RPDs. When the LASAR-155's RRM has

assembled a packet, it attaches the RPDR of the RPD describing the packet to the

RPDRR Queue. For multiple RPD packets, only the first RPD's RPDR of the linked

list is attached. Please refer below.

PM7375-SC Datasheet(PDF) 93 Page - PMC-Sierra, Inc