PM7367 datasheet(68/323 Pages) PMC

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PM7367 FREEDM-32P32

DATA SHEET

PMC-1991499

ISSUE 2

FRAME ENGINE AND DATA LINK MANAGER

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

packet status information associated with the data in each buffer. TDs are

transferred from the TMAC to the host and vice versa using descriptor reference

queues. The TMAC maintains all the pointers for the operation of the queues.

The TMAC acquires buffers with data ready for transmission by reading TDRs

from a TDR ready queue. After a packet has been transmitted, the TMAC places

the associated TDR onto a TDR free queue.

To minimise host bus accesses, the TMAC maintains a descriptor reference table

to store current DMA information. This table contains separate DMA information

entries for up to 32 transmit channels. The TMAC also performs per-channel

sorting of packets received in the TDR ready queue to eliminate head-of-line

blocking.

8.6.1 Data Structures

The TMAC communicates with the host using Transmit Descriptors (TD),

Transmit Descriptor References (TDR), the Transmit Data Reference Ready

(TDRR) queue and the Transmit Data Reference Free (TDRF) queue.

The TMAC reads packet data from data buffers in host memory. The TD, TDR,

TDRR queue, and TDRF queue are data structures which are used to transfer

host memory data buffer information. All four data structures are manipulated by

both the TMAC and the host computer. The TD holds the data buffer size, data

buffer address, and other packet information. The TDR is a pointer which is

used to index into a table of TDs. The TDRR queue and TDRF queue allow the

TMAC and the host to pass TDRs back and forth. These data structures are

described in more detail in the following sections.

Transmit Descriptor

The Transmit Descriptors (TDs) pass buffer and packet information between the

TMAC and the host. Both the TMAC and the host read and write information in

the TDs. TDs are stored in host memory in a Transmit Descriptor Table. The

Transmit Descriptor structure is shown in Figure 10.

Figure 10 – Transmit Descriptor

Reserved (5)

TCC[6:0]

Bytes In Buffer [15:0]

Transmit Buffer Size [15:0]

Data Buffer Start Address [31:0]

Host Next TD Pointer [13:0]

TMAC Next TD Pointer [13:0]

Bit 31

Bit 0

IOC

ABT

Reserved (16)

Res(2)

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