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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
55
channels. The TMAC also performs per-channel sorting of packets received in the TDR ready
queue to eliminate head-of-line blocking.
9.6.1
Data Structures
The TMAC communicates with the host using Transmit Descriptors (TD), Transmit Descriptor
References (TDR), the Transmit Data Reference Ready (TDRR) queue and the Transmit Data
Reference Free (TDRF) queue.
The TMAC reads packet data from data buffers in host memory. The TD, TDR, TDRR queue, and
TDRF queue are data structures which are used to transfer host memory data buffer information.
All four data structures are manipulated by both the TMAC and the host computer. The TD holds
the data buffer size, data buffer address, and other packet information. The TDR is a pointer
which is used to index into a table of TDs. The TDRR queue and TDRF queue allow the TMAC
and the host to pass TDRs back and forth. These data structures are described in more detail in
the following sections.
Transmit Descriptor
The Transmit Descriptors (TDs) pass buffer and packet information between the TMAC and the
host. Both the TMAC and the host read and write information in the TDs. TDs are stored in host
memory in a Transmit Descriptor Table. The Transmit Descriptor structure is shown in Figure 10.
Figure 10 – Transmit Descriptor
M
V
Reserved (5)
TCC[6:0]
Bytes In Buffer [15:0]
Transmit Buffer Size [15:0]
Data Buffer Start Address [31:0]
Host Next TD Pointer [13:0]
TMAC Next TD Pointer [13:0]
Bit 31
CE
Bit 0
IOC
ABT
Reserved (16)
Res(2)
P
Table 11 – 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.