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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
August 2006
Developer’s Manual
Reference Number: 306262-004US
945
AHB Queue Manager (AQM)—Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network
Processors
27.6.11
Queue Configuration Words 0 - 63
The 64 queue configuration words are located in internal SRAM and require initialization
before AQM usage. The read and write pointers need to be cleared on initialization,
because this reflects an empty queue. A system reset sets the status registers to
reflect empty queues, but until the queue configuration words have been set, this state
is somewhat inconsistent. On a write accesses to any of the Queue Configuration Words
0-31, the corresponding queue status is communicated on the Flag Bus. When the AQM
is fully configured, use these configuration words for read-only purposes, to monitor
queue pointers. Resetting a queue requires two operations. First the appropriate queue
status flags must be configured, then the Queue Configuration Word must be set. The
data format for the Queue Configuration Word is shown in the QUECONFIG register.
If the queue configuration word has not been initialized, reading or writing to a queue
produces undefined operations, and can cause spurious parity errors and/or data
corruption of another queue.
Register Name:
QUECONFIG (0 <= n <=63)
Block
Base Address:
Queue #n 0x2000
Offset Address
+ 4n
Reset Value
0xUUUUUUUU
Register Description:
Queue #n configuration word located in SRAM.
Access:
(See below.)
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
8
7
6
5
4
3
2
1
0
Queue (n)
NF
Watermark
Queue (n)
NE
Watermark
Q (n)
Buffer
Size
Q (n)
Entry
Size
Queue (n) Base Address
Queue (n) Read Pointer
Queue (n) Write Pointer
Register
QUECONFIG (0 <= n <=63)
Bits
Name
Description
Reset
Value
Access
31:2
9
Nearly Full
Watermark
These bits configure the Nearly Full Watermark, to 0 (“000”), 1 (“001”), 2 (“010”),
04(“011”), 8 (“100”), 16 (“101”), 32 (“110”), or 64 (“111”) entries from the top of
the queue. The usable range of Nearly Full Watermark selection must be less than
the buffer size.
U
RW
28:2
6
Nearly Empty
Watermark
These bits configure the Nearly Empty Watermark, to 0 (“000”), 1 (“001”), 2
(“010”), 04(“011”), 8 (“100”), 16 (“101”), 32 (“110”), or 64 (“111”) entries from
the bottom of the queue. The usable range of Nearly Empty Watermark selections
must be less than the buffer size.
U
RW
25:2
4
Buffer Size
These bits configure the queue buffer size. The buffer size can be configured for
16 (“00”), 32 (“01”), 64 (“10”) or 128 (“11”) words.
U
RW
23:2
2
Entry Size
These bits configure the queue entry size of the queue. The entry size can be set
at 1 (“00”) or 2 (“01”) or 4 (“10”) words. An input of “11” sets the entry size to 1.
U
RW
21:1
4
Base Address
This field configures the starting base address of the queue. The read and write
pointer are offset addresses from the base address. This base address is a SRAM
16 word address. (In other words, this value needs to be multiplied by 16 to get
the SRAM address. Also, this value is a word address, not a byte address as the
queue has no notion of bytes.) Base addresses, 00 to 03, are reserved for the
Queue Configuration Words. The most significant bit of the base address is
reserved for growth to a 16 KB SRAM to provide 8 KB of additional queue buffer
space. BIt 21 is implemented (i.e. can be read and written) but will cause an
address wrap (e.g. 0x00 and 0x80 point to the same region in SRAM).
U
RW
13:7
Read Pointer
Pointer to the next entry to read from the queue. The pointer is the AQM’s internal
SRAM word address. This pointer should be initialized to zero, and should be
written only for diagnostic or test purposes.
U
RW
6:0
Write Pointer
Pointer to the next entry to write to the queue. The pointer is the AQM’s internal
SRAM word address. This pointer should be initialized to zero, and should be
written only for diagnostic or test purposes.
U
RW