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RELEASED
DATA SHEET
PM7382 FREEDM-32P256
ISSUE 3
PMC-2010333
FRAME ENGINE AND DATA LINK MANAGER 32P256
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA,INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
70
Transmit Channel Descriptor Reference Table
The TMAC256 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 TMAC256 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 14 below.
Figure 14 – Transmit Channel Descriptor Reference Table
Current TD Pointer [14:0]
Last TD Pointer [14:0]
Host TD Pointer [14:0]
DMA Current Address[31:0]
Bit 0
Bit 33
TCC 0, Pri 0
TCC 671, Pri 1
Bytes to Tx [15:0]
Reserved (12)
Res
Next TD Pointer [14:0]
D
A
M CE
IOC
Abrt
PiP
NA
U
Res
V
TCC 1, Pri 0
Current TD Pointer [14:0]
Last TD Pointer [14:0]
Host TD Pointer [14:0]
DMA Current Address[31:0]
Bytes to Tx [15:0]
Reserved (12)
Res
Next TD Pointer [14:0]
D
A
M CE
IOC
Abrt
PiP
NA
V
Current TD Pointer [14:0]
Last TD Pointer [14:0]
Host TD Pointer [14:0]
DMA Current Address[31:0]
Bytes to Tx [15:0]
Reserved (12)
Res
Next TD Pointer [14:0]
D
A
M CE
IOC
Abrt
PiP
NA
V
U
Res
U
Res
Res
Res
Res
Res
Res
Res