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Intel
®
IXP42X Product Line of Network Processors and IXC1100 Control Plane Processor
September 2006 DM
Order Number: 252480-006US 561
AHB Queue Manager (AQM)—Intel
®
IXP42X product line and IXC1100 control plane processors
than or equal to the full watermark, the queue is considered nearly full. If the number
of completely full entries is less than or equal to the empty watermark, the queue is
considered nearly empty.
Of course, status may be read at any time by an AHB read of the appropriate status
register. The status read will reflect the status of the queue at the time of the read,
respecting all previous AHB operations. By example, if two closely spaced AHB reads
are performed, one to a queue and another to that queue’s status register, the status
register read will reflect the completion of the queue read. This will require that the
second read have additional wait states inserted (by hardware) into the bus operation
in order to insure that the first operation has been completed.
The operation of the Nearly Full, Nearly Empty, Full and Empty Status Flags with the
Nearly Empty & Nearly Full watermarks set to various levels is demonstrated in
Table 177. For this example, the buffer size is set to 64 and the entry size is set to 1.
When the watermarks are set to zero, the Nearly Empty and Empty Flags will be
identical and the Nearly Full and Full Flags will be identical.
Please note in the following table the “# Entries in the Queue” represents the cardinal
number of entries in the queue for each watermark value.
21.4.2.2 Flag Bus
Status, for queues 0-31 only, will be directly communicated to the NPE via a dedicated
interface, referred to as the Flag Bus. The Flag Bus is composed of 4 independent
strobe signals, aqm_flag_strb[3:0], a queue identification bus, aqm_flag_que_id[4:0],
and a queue status bus, aqm_flag_que_stat[3:0]. The queue status bus will provide
the empty, nearly empty, nearly full and full status flags respectively on bits 0-3 of the
Table 177. Queue Status Flags
Nearly Empty
Watermark
Nearly Full
Watermark
# Entries in the
Queue
ENENFF
0 (000) 0 (000)
0
1 – 62
63
1
0
0
1
0
0
0
0
1
0
0
1
1 (001) 1 (001)
0
1
2 – 61
62
63
1
0
0
0
0
1
1
0
0
0
0
0
0
1
1
0
0
0
0
1
2 (010) 2 (010)
0
1 – 2
3 - 60
61 – 62
63
1
0
0
0
0
1
1
0
0
0
0
0
0
1
1
0
0
0
0
1
4 (011) 4 (011)
0
1 – 4
5 – 58
59- 62
63
1
0
0
0
0
1
1
0
0
0
0
0
0
1
1
0
0
0
0
1
8 (100) 8 (100)
0
1 - 8
9 – 54
55 - 62
63
1
0
0
0
0
1
1
0
0
0
0
0
0
1
1
0
0
0
0
1