PM7366-PI datasheet(74/286 Pages) PMC

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PM7366 FREEDM-8

DATA SHEET

PMC-1970930

ISSUE 4

FRAME ENGINE AND DATA LINK MANAGER

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

Table 12 – Transmit Descriptor Reference

Bit 16

Bit 0

STATUS[2:0]

TDR[13:0]

Field

Description

Status[2:0]

The TMAC fills in the Status field to indicate to the host the results of

processing the TD. The encoding is:

Status[1:0]

Description

Last or only buffer of packet, buffer read.

Buffer of partial packet, buffer read.

Unprovisioned channel, buffer not read.

Malformed packet (e.g. Bytes In Buffer field set to 0),

buffer not read.

Status[2]

Description

No underflow detected.

Underflow detected.

TDR[13:0]

The TDR[13:0] field contains the offset of the TD returned.

If a TDR is returned to the host with the status field set to “10” (unprovisioned channel), the TDR

may point to a binary tree of TDs and buffers (as indicated by the CE and V bits in the TDs). It is

the responsibility of the host to traverse the tree to reclaim all the buffers. If a TDR is returned to

the host with the status field set to any other value, the TDR will only point to one TD and buffer

regardless of the values of V and CE in that TD.

The underflow status bit (Status[2]) is normally attached to the TDR belonging to a packet

experiencing underflow. For long packets spanning multiple buffers, underflow is reported only

once at the first available TDR of that channel. All subsequent TDRs of that packet will be

returned normally without the underflow status. In rare cases, due to internal buffering by the

FREEDM-8, a packet may experience underflow at the very end of a packet, just as the TDR is

being returned to the TDR free queue. The underflow status will then be reported in the first TDR

of the immediate next packet of that channel. Because of the uncertainty with the reporting of

underflows between the current verse the subsequent packet, the underflow status should only be

used to gather performance statistics on channels and not for initiating packet specific responses

such as retransmission.

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