
DATA SHEET
PM7367 FREEDM-32P32
ISSUE 2
PMC-1991499
FRAME ENGINE AND DATA LINK MANAGER
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMER’S INTERNAL USE
55
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.
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.