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PM73487 QRT
PMC-Sierra, Inc.
PMC-980618
Issue 3
622 Mbps ATMTraffic Management Device
Released
Datasheet
152
8.2.1
Transmit Service Class Queue (TX SCQ) Control Block
Base address: 100000
h
(400000
h
byte)
Index: 4
h
Number of entries: 496 (1984 words)
Type: Read/Write
Long Address = 100000
h
+
40
h
×
VO +
4
h
×
service_class
+
offset
Byte Address = 400000
h
+100
h
×
VO +
10
h
×
service_class
+
offset
8.2.1.1
TX_SCQ_CONFIG
Offset: 0
h
(0
h
byte)
Type: Read/Write
Format: Refer to the following table.
Table 26. Transmit Service Class Queue (TX SCQ) Control Block Summary
Byte
Offset
Long
Offset
Name
Read or
Write
Description
0
h
0
h
TX_SCQ_CONFIG
R/W
The exponents of the maximum and congested queue
depths for this SC.
4
h
1
h
TX_SCQ_STATE
R/W
(init only)
The current queue depth and congestion state for this
SC.
8
h
2
h
TX_SCQ_HEAD/
TX_SCQ_OUT_FIFO_HEAD
R/W
(init only)
For non-multicast queues, this is the head of the
linked list. For multicast queues, this is the FIFO
read pointer.
C
h
3
h
TX_SCQ_TAIL/
TX_SCQ_OUT_FIFO_TAIL
R/W
(init only)
For non-multicast queues, this is the tail of the linked
list. For multicast queues, this is the FIFO write
pointer.
Field (Bits)
Description
Not present
(31:16)
RAM is not present in these bit locations.
TX_SCQ_EXP_MAX_QD
(15:12)
Exponent of the maximum per-SC queue depth. Initialize to the proper setting. Limits
the TX_SCQ_CUR_QD to:
TX_SCQ_CUR_QD
≤
1 + 2
TX_SCQ_EXP_MAX_QD
A value of 0
h
causes all cells for this SCQ to be dropped. A value of F
h
limits this SC to
31744 cells.
TX_SCQ_EXP_CONG_QD
(11:8)
Exponent of the congested per-SCQ queue depth. Initialize to the proper setting. The
congestion state is entered when the threshold is exceeded, and the congestion state is
exited when the queue length drops below 50 percent of this threshold. Enables conges-
tion management when:
TX_SCQ_CUR_QD > 1 + 2
TX_SCQ_EXP_CONG_QD
A value of 0
h
causes this SCQ to be in congestion at all times. A value of 1
h
may not be
used. A value of F
h
causes this SCQ to enter congestion at a depth of 31744 cells.