PM7384 FREEDM-84P672
DATA SHEET
PMC-1990445
ISSUE 5
FRAME ENGINE AND DATA LINK MANAGER 84P672
Table 12 – Transmit Descriptor Reference
Bit 17
Bit 0
STATUS[2:0]
TDR[14:0]
Field
Description
Status[2:0]
The TMAC672 fills in the Status field to indicate to the
host the results of processing the TD. The encoding is:
Status[1:0] Description
00
01
10
11
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
0
No underflow detected.
1
Underflow detected.
TDR[14:0]
The TDR[14:0] 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-84P672, 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.
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
67
PMC [ PMC-SIERRA, INC ]
