PM7367 datasheet(69/323 Pages) PMC

69 / 323 page

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

Table 9 – Transmit Descriptor Fields

Field

Description

Data Buffer Start

Address [31:0]

The Data Buffer Start Address[31:0] bits point to the

data buffer in host memory.

The Data Buffer Start Address field is valid in all TDs

Bytes In Buffer [15:0]

The Bytes In Buffer[15:0] field is used by the host to

indicate the total number of bytes to be transmitted in

the current TD. Zero length buffers are illegal.

The Priority bit is set by the host to indicate the

priority of the associated packet in a two level quality

of service scheme. Packets with its P bit set high are

queued in the high priority queue in the TMAC.

Packets with the P bit set low are queued in the low

priority queue. Packets in the low priority queue will

not begin transmission until the high priority queue is

empty.

The V bit is used to indicate that the TMAC Next TD

Pointer field is valid. When set to logic 1, the TMAC

Next TD Pointer[13:0] field is valid. When V is set to

logic 0, the TMAC Next TD Pointer[13:0] field is

invalid. The V bit is used by the host to reclaim data

buffers in the event that data presented to the TMAC

is returned to the host due to a channel becoming

unprovisioned. The V bit is expected to be initialised

to logic 0 by the host.

The More (M) bit is used by the host to support

packets that require multiple TDs. If M is set to

logic 1, the current TD is just one of several TDs for

the current packet. If M is set to logic 0, this TD

either describes the entire packet (in the single TD

packet case) or describes the end of a packet (in the

multiple TD packet case).

Note: When M is set to logic 1, the only valid value

for CE is logic 0.

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