PM73121ꢀAAL1gator II
Data Sheet
PMC-Sierra, Inc.
PMC-980620
,VVXHꢀꢁ
AAL1 SAR Processor
POTENTIAL SYSTEM IMPACTS
Hardware Considerations
The AAL1gator II device is pin-for-pin compatible with the WAC-021-CX. However, the
following hardware issues are items to consider.
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The DS3 mode requires a 40 MHz system clock to maintain throughput.
Power consumption for the AAL1gator II is about 300 mW higher than for the WAC-021-
CX device.
Software Considerations
The first two issues are addressed by PMC-Sierra’s AAL1gator II software Device Control
Package.
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The math table was modified to support E1 and T1 lines at the same time. This was
required since the WAC-021-CX has a different math table for E1 lines than for T1 lines.
The PM73121 can configure some lines in E1 mode and some lines in T1 mode. As a
result, only one math table is required and anyone using E1 SDF-MF mode needs to use
the new math table.
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New counters have to been added to support the CES MIB. These count values will
automatically be written into memory at previously unused locations.
The PM73121 calculates buffer overflow as data is written into memory. The WAC-021-
CX calculates buffer overflow only at the start of a cell being written into memory.
Because of this difference in calculating buffer overflow, it is possible that a queue
configured with a certain MAX_BUF size with the WAC-021-CX may show an overflow
with the PM73121.
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The SNP algorithm has been changed to conform with the “Fast Algorithm”, as specified
in the ITU-T Recommendation I.363.1. The new algorithm is more tolerant to single
errors and lost cells and has a slightly different behavior. Typically this is transparent to
users, unless they are injecting errors. However, one side effect of the new algorithm is
that the first cell received for any queue is always dropped. This is not an issue for most
applications since there is always a start-up period before any real data is contained in the
cells. However, if an application exists that is sensitive to the loss of the first cell, a new
control bit has been added to disable dropping the first cell (refer to
“NODROP_IN_START” on page 161). This bit defaults to off.
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The INCORRECT_SNP counter (refer to “R_INCORRECT_SNP Word Format” on page
158) has been changed to conform to the CES Management Information Base (MIB). That
is, all cells with an incorrect SNP field will be counted, regardless of whether or not the
SN was corrected. (In the WAC-021-CX only non-correctable SNPs were counted.)
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PMC [ PMC-SIERRA, INC ]
