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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
56
Field
Description
P
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.
V
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.
M
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.
CE
The Chain End (CE) bit is used by the host to indicate the end of
a linked list of TDs presented to the TMAC. The linked list can
contain one or more packets as delineated by the M bit (see
above). When CE is set to logic 1, the current TD is the last TD
of a linked list of TDs. When CE is set to logic 0, the current TD
is not the last TD of a linked list. When the current TD is not the
last of the linked list, the Host Next TD Pointer[13:0] field is valid,
otherwise the field is not valid.
Note: When CE is set to logic 1, the only valid value for M is
logic 0.
Note: When presenting raw (i.e. unpacketised) data for
transmission, the host should code the M and CE bits as for a
single packet chain, i.e. M=1, CE=0 for all TDs except the last in
the chain and M=0, CE=1 for the last TD in the chain.
TCC[6:0]
The Transmit Channel Code (TCC[6:0]) field is used by the host
to indicate with which channel a TD is associated. All TD in a
chain must be associated with the same channel, i.e. have this
field set to the same value.