Released
Datasheet
PM73487 QRT
PMC-Sierra, Inc.
PMC-980618
Issue 3
622 Mbps ATM Traffic Management Device
8.2.1 Transmit Service Class Queue (TX SCQ) Control Block
Base address: 100000h (400000h byte)
Index: 4h
Number of entries: 496 (1984 words)
Type: Read/Write
Long Address = 100000 + 40 × VO + 4 × service_class + offset
h
h
h
Byte Address = 400000h +100h × VO + 10h × service_class + offset
Table 26. Transmit Service Class Queue (TX SCQ) Control Block Summary
Byte
Offset Offset
Long
Read or
Write
Name
Description
0h
4h
8h
0h
1h
2h
TX_SCQ_CONFIG
R/W
The exponents of the maximum and congested queue
depths for this SC.
TX_SCQ_STATE
R/W
(init only)
The current queue depth and congestion state for this
SC.
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.
Ch
3h
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.
8.2.1.1 TX_SCQ_CONFIG
Offset: 0h (0h byte)
Type: Read/Write
Format: Refer to the following table.
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 + 2TX_SCQ_EXP_MAX_QD
A value of 0h causes all cells for this SCQ to be dropped. A value of Fh 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 + 2TX_SCQ_EXP_CONG_QD
A value of 0h causes this SCQ to be in congestion at all times. A value of 1h may not be
used. A value of Fh causes this SCQ to enter congestion at a depth of 31744 cells.
152
PMC [ PMC-SIERRA, INC ]
