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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
62
Transmit Channel Descriptor Reference Table
The TMAC maintains a Transmit Channel Descriptor Reference (TCDR) table in which is stored
certain information relating to DMA activity on each channel together with TD pointers which are
used by the TMAC to sort packet chains supplied by the host into per-channel linked lists (see
below). The caching of DMA-related information reduces the number of host bus accesses
required to process each data packet, while the sorting into per-channel linked lists eliminates
head of line blocking. Each channel is provided with two entries in the TCDR table, one for high
priority packets (Pri 1) and one for low priority packets (Pri 0). The structure of the TCDR table is
shown in Figure 13 below.
Figure 13 – Transmit Channel Descriptor Reference Table
M CE
Last TD Pointer [13:0]
A
D
Current TD Pointer [13:0]
Bytes to Tx [15:0]
AbrtIOC
Host TD Pointer [13:0]
DMA Current Address [31:0]
Reserved
M CE
Last TD Pointer [13:0]
A
D
Current TD Pointer [13:0]
Bytes to Tx [15:0]
AbrtIOC
Host TD Pointer [13:0]
DMA Current Address [31:0]
M CE
Last TD Pointer [13:0]
A
D
Current TD Pointer [13:0]
Bytes to Tx [15:0]
AbrtIOC
Host TD Pointer [13:0]
DMA Current Address [31:0]
:
:
:
Bit 31
Bit 0
TCC 0, Pri 0
TCC 1, Pri 0
TCC 127, Pri 1
Next TD Pointer [13:0]
Reserved
Next TD Pointer [13:0]
Reserved
Next TD Pointer [13:0]
V
V
V
Last
M
U
NA
Last
M
U
NA
Last
M
U
NA
PiP
PiP
PiP
Table 13 – Transmit Channel Descriptor Reference Table Fields
Field
Description
M
A copy of the M bit in the TD currently being read.
CE
A copy of the CE bit in the TD currently being read.
Last TD Pointer [13:0]
Offset to the head of the last host-linked chain of TDs to be read.
(See Figure 14)