Data Validity Cases And Their Handling - Intel IXP45X Developer's Manual

Intel
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.
Table 295.

Data Validity Cases and Their Handling

Case
Unsupported bus
operation
Out of range SRAM
address
Reading incorrect
number of queue
words
Queue overflow on
write
Queue underflow on
read
Parity error without
parity detection
enabled
Parity error on data
during queue read
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.
® ®
Intel IXP45X and Intel IXP46X Product Line of Network Processors
Developer's Manual
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IXP45X and Intel IXP46X Product Line of Network Processors—AHB Queue Manager
Hardware
Signal
Data Abort fault to Intel XScale
Error to AHB COP
AHB Error
Target Abort to PCI
response
Forced parity error to expansion bus - may result in
silent data corruption if expansion device ignores
parity.
None Zero value returned on all reads, writes ignored.
None Zero value returned on all reads, writes ignored.
None Status flag set.
None Status flag set, zero value returned
None, will most probably result in silent corrupted
None
data.
Data Abort fault to Intel XScale
Error to AHB COP
Target Abort to PCI
AHB Error
Forced parity error to expansion bus - may result in
response
silent data corruption if expansion device ignores
parity.
Interrupt signal to Intel XScale processor
Software Signal
®
Processor
®
Processor
Reference Number: 306262-004US
(AQM)
Recovery
None
Detect zero value,
handle as exception
Detect zero value,
handle as exception
None, data is lost.
Detect zero value,
handle as exception
None
Reset and restart
application usage of
AQM
August 2006