PM7375-SC datasheet(78/430 Pages) PMC

78 / 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

9.14.2 Transmit Request Machine

The transmit DMA channels are controlled using the Transmit Request Machine

(TRM). The TRM receives segmentation requests from the TATS block, retrieves

packet bytes using the PCI Interface and provides the bytes to the TALP block for

inclusion into cells. All transmit DMA data transfer actions are performed with

minimum PCI Host interaction with the aid of internal per VC storage.

PCI Host communication is provided using Transmit Descriptors (TD), a Transmit

Descriptor Reference Free (TDRF) Queue and a Transmit Descriptor Reference

Ready (TDRR) High and Low priority Queues. All four data structures are found in

the PCI Host memory space and are referenced using LASAR-155 registers. A TD

is a thirty-two byte data structure which can be used by the PCI Host to describe a

packet or a portion of a packet. The TD data structure is fully described below in the

Transmit Descriptor Section.

9.14.3 Transmit Descriptor Table

Each TD resides in the Transmit Descriptor Table in the PCI Host memory. The

Transmit Descriptor Table can contain a maximum of 16384 TDs. The based of the

Transmit Descriptor Table is user programmable using the PCID Transmit

Descriptor Table Base (TDTB) register. As shown below, each TD can be located

using a Transmit Descriptor Reference (TDR) combined with the TDTB register.

PM7375-SC Datasheet(PDF) 78 Page - PMC-Sierra, Inc