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RELEASED
DATA SHEET
PM7366 FREEDM-8
ISSUE 4
PMC-1970930
FRAME ENGINE AND DATA LINK MANAGER
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA,INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
61
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
00
Last or only buffer of packet, buffer read.
01
Buffer of partial packet, buffer read.
10
Unprovisioned channel, buffer not read.
11
Malformed packet (e.g. Bytes In Buffer field set to 0),
buffer not read.
Status[2]
Description
0
No underflow detected.
1
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.