PM7375-SC datasheet(91/430 Pages) PMC

91 / 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

9.14.6 Receive Request Machine

The receive DMA channel is controlled using the Receive Request Machine (RRM).

The RRM receives cell payloads associated with an open VC from the RALP block.

Payloads are assumed to be either management cells or part of a packet under

reassembly. For management cells, the payload is burst written into PCI Host

memory and the host is alerted. Some flexibility is provided to allow for the

accumulation of several cells before the PCI Host is alerted. For payloads of

packets under reassembly, the payload is burst written into PCI Host memory but

the PCI Host is not alerted until the complete packet has been reassembled. All

DMA burst data transfers are performed with minimum PCI Host interaction with the

aid of internal per VC storage.

For packets, PCI Host communication is provided using Receive Packet Descriptors

(RPD), a Receive Packet Descriptor Reference Small Buffer Free (RPDRSF)

Queue, a Receive Packet Descriptor Reference Large Buffer Free (RPDRLF)

Queue and a Receive Packet Descriptor Reference Ready (RPDRR) Queue. Two

free queues are provided to allow for flexible buffer sizes. For large buffers the

RPDRLF Queue and for small buffers the RPDRSF Queue. All four data structures

are located in PCI Host memory. A RPD is a thirty two byte data structure set up by

the PCI Host and used by the LASAR-155 to describe a packet or a portion of a

packet. The RPD data structure is fully described in the Receive Packet Descriptor

Section.

For management cells, PCI Host communication is provided using Receive

Management Descriptors (RMD), a Receive Management Descriptor Reference

Free (RMDRF) Queue and a Receive Management Descriptor Reference Ready

(RMDRR) Queue. All three data structures are located in PCI Host memory. A

RMD is a thirty two byte data structure set up by the PCI Host and used by the

LASAR-155 to describe a management cell. The RMD data structure is fully

described in the Receive Management Descriptor Section.

9.14.7 Receive Packet Descriptor Table

Each RPD resides in the Receive Packet Descriptor Table. The Receive Packet

Descriptor table can contain a maximum of 16384 RPDs. The base of the Receive

Packet Descriptor Table is user programmable via the PCID Rx Packet Descriptor

Table Base register. Thus, as shown below, a RPD can be located using a Receive

Packet Descriptor Reference (RPDR) combined with the PCID Rx Packet Descriptor

Table Base register.

PM7375-SC Datasheet(PDF) 91 Page - PMC-Sierra, Inc