
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
54
packet status information associated with the data in each buffer. TDs are
transferred from the TMAC to the host and vice versa using descriptor reference
queues. The TMAC maintains all the pointers for the operation of the queues.
The TMAC acquires buffers with data ready for transmission by reading TDRs
from a TDR ready queue. After a packet has been transmitted, the TMAC places
the associated TDR onto a TDR free queue.
To minimise host bus accesses, the TMAC maintains a descriptor reference table
to store current DMA information. This table contains separate DMA information
entries for up to 32 transmit channels. The TMAC also performs per-channel
sorting of packets received in the TDR ready queue to eliminate head-of-line
blocking.
8.6.1 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