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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors—AHB Queue Manager
(AQM)
Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
Developer’s Manual
August 2006
936
Reference Number: 306262-004US
requires essentially a complete software reset of the AQM and in general any stored
data is invalid. To accomplish this software reset, the AQM must have parity disabled
and the entire memory should be reinitialized. After reinitialization “normal” operation
may resume, although obviously any stored data is now destroyed.
27.4.4
Data Validity
The AHB queue manager can produce “incorrect” data under certain contexts, and
these contexts need to be understood. Some of these cases represent incorrect
software usage of the AQM, others represent hardware conditions. The following table
summarizes the cases where the AQM does not return “valid” data, how a software
stack will be notified and what (if anything) can be done.
As described elsewhere, not all AHB cycle types are supported, with certain ones
automatically producing an Error response. The data returned for these cases is not
defined.
Data returned for out-of-range SRAM access or MMR access is always zero and no error
condition is signaled. If software should attempt reads or writes of out-of-range
addresses, there will not be any obvious notification except that the data read will be
zero and data written will be ignored.
Reading (for example) two words out of a single word queue will return data for the
first word and zeros for the second word. The fact that the second word is not defined
is not signalled. In general, a mismatch between the number of words in the entry
between the actual usage and the configuration word definition will either result in lost
data (i.e. as if it were overflow) or zeros.
Table 295.
Data Validity Cases and Their Handling
Case
Hardware
Signal
Software Signal
Recovery
Unsupported bus
operation
AHB Error
response
Data Abort fault to Intel XScale
®
Processor
Error to AHB COP
Target Abort to PCI
Forced parity error to expansion bus - may result in
silent data corruption if expansion device ignores
parity.
None
Out of range SRAM
address
None
Zero value returned on all reads, writes ignored.
Detect zero value,
handle as exception
Reading incorrect
number of queue
words
None
Zero value returned on all reads, writes ignored.
Detect zero value,
handle as exception
Queue overflow on
write
None
Status flag set.
None, data is lost.
Queue underflow on
read
None
Status flag set, zero value returned
Detect zero value,
handle as exception
Parity error without
parity detection
enabled
None
None, will most probably result in silent corrupted
data.
None
Parity error on data
during queue read
AHB Error
response
Data Abort fault to Intel XScale
®
Processor
Error to AHB COP
Target Abort to PCI
Forced parity error to expansion bus - may result in
silent data corruption if expansion device ignores
parity.
Interrupt signal to Intel XScale processor
Reset and restart
application usage of
AQM