PM7384 FREEDM-84P672
DATA SHEET
PMC-1990445
ISSUE 5
FRAME ENGINE AND DATA LINK MANAGER 84P672
Field
Description
TMAC Next TD Pointer The TMAC Next TD Pointer[14:0] bits are used to
[14:0]
store TDRs which permits the TMAC672 to create
linked lists of TDs passed to it via the TDRR queue.
The TDs are linked with other TDs belonging to the
same channel and same priority level. In the case
that data presented to the TMAC672 is returned to
the host due to a channel becoming unprovisioned, a
TDR pointing to the start of the per-channel linked list
of TDs is placed on the TDRF queue. It is the
responsibility of the host to follow the TMAC672 and
host links in order to recover all the buffers.
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.
Host Next TD Pointer
[14:0]
The Host Next TD Pointer[14:0] bits are used to store
TDRs which permits the host to support linked lists of
TDs. As described above, linked lists of TDs are
terminated by setting the CE bit to logic 1. Linked
lists of TDs are used by the host to pass multiple TD
packets or multiple packets associated with the same
channel and priority level to the TMAC672.
Transmit Buffer Size
[15:0]
The Transmit Buffer Size[15:0] field is used to
indicate the size in bytes of the current TD's data
buffer. (N.B. The TMAC672 does not make use of
this field.)
Transmit Descriptor Table
The Transmit Descriptor Table, which resides in host memory, contains all of the
Transmit Descriptors referenced by the TMAC672. To access a TD, the
TMAC672 takes a TDR from a TDRR queue or from the TCDR table and adds
16 times its value (because each TD is 16 bytes in size) to the Transmit
Descriptor Table Base (TDTB) pointer to form the actual address of the TD in
host memory. Each TD must reside in the Transmit Descriptor Table. The
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
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PMC [ PMC-SIERRA, INC ]
