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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
August 2006
Developer’s Manual
Reference Number: 306262-004US
937
AHB Queue Manager (AQM)—Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network
Processors
On the overflow condition, the written data is permanently lost. On the underflow
condition, the data returned is zero.
If there are parity errors where the parity notification is not enabled, the data returned
represents the data containing the parity error. If parity notification is enabled and the
entry contains a parity error, the error is signaled on that particular bus cycle and
consistent with the AHB specification, the master has the option of terminating a burst
operation on the first error.
In general, a software usage model should treat the return of zero data as a suspicious
case and the data type stored in the AQM should take this into account. If the data type
were to be memory address pointers, this is well behaved since a null pointer is not
defined. Other data types should take this into account.
27.4.5
Burst Operations to Queues
Burst operations are useful for writing multiple entry queues. An INCR4 burst can fill an
entire entry for a four entry queue without having to re-arbitrate for ownership of the
AHB bus, which enhances performance. However, if the burst type does not match the
entry size for the queue, the transaction data to the inactive queue entries is simply
dropped. In general, software should avoid burst transactions to queues that have
fewer words per entry than the burst because of the decreased performance.
27.5
Detailed Register Descriptions
*
Table 296.
Register Legend
Attribute
Legend
Attribute
Legend
RV
Reserved
RC
Read Clear
PR
Preserved
RO
Read Only
RS
Read/Set
WO
Write Only
RW
Read/Write
NA
Not Accessible
RW1C
Normal Read
Write ‘1’ to clear
RW1S
Normal Read
Write ‘1’ to set
Table 297.
Register Summary (Sheet 1 of 2)
Address
Register Name
Description
Reset Value
Access
0x60000000
QUEACC0_0
Queue 0 word 0 data register
N/A
RW
0x60000004
QUEACC0_1
Queue 0 word 1 data register (used only when Queue 0
has a entry size of 2 or 4)
N/A
RW
0x60000008
QUEACC0_2
Queue 0 word 2 data register (used only when Queue 0
has a entry size of 4)
N/A
RW
0x6000000C
QUEACC0_3
Queue 0 word 3 data register (used only when Queue 0
has a entry size of 4)
N/A
RW
0x60000010
QUEACC1_0
Queue 1 word 0 data register
N/A
RW
0x60000014
QUEACC1_1
Queue 1 word 1 data register (used only when Queue 1has
a entry size of 2 or 4)
N/A
RW
0x60000018
QUEACC1_2
Queue 1 word 2 data register (used only when Queue 1has
a entry size of 4)
N/A
RW
0x6000001C
QUEACC1_3
Queue 1 word 3 data register (used only when Queue 1has
a entry size of 4)
N/A
RW