
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
64
Field
Description
Host TD Pointer [13:0] A copy of the Host Next TD Pointer field of the TD
currently being read, i.e. a pointer to the next TD in the
chain currently being read. (See Figure 14)
DMA Current
Address[31:0]
The DMA Current Address [31:0] bits hold the address
of the next dword in the current buffer. This field is
incremented on each access to the buffer.
V
Indicates if the linked list of packets for this channel
contains more than one host-linked chain (See Figure
14). If the V bit is set to logic 1, the list contains more
than one chain and the next and last TD pointer fields
are valid. If the V bit is set to logic 0, the list is either
empty or contains only one host-linked chain and the
next and last TD pointer fields are invalid.
Next TD Pointer [13:0] Offset to the head of the next host-linked chain of TDs
to be read. (See Figure 14)
Transmit Descriptor Linking
As described above, the TCDR table contains pointers which the TMAC uses to
construct linked lists of data packets to be transmitted. After the host places a
new TDR in the TDR Ready queue, the TMAC retrieves the TDR and links it to
the TD pointed at by the Last TD Pointer field. The TMAC may create up to 256
linked lists, viz. a high-priority list and a low-priority list for each DMA channel.
Whenever a new data packet is requested by the downstream block, the TMAC
picks a packet from the high-priority linked list unless it is empty, in which case, a
packet from the low-priority linked list is used.