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PM7329 S/UNI-APEX-1K800
DATASHEET
PMC-2010141
ISSUE 2
ATM TRAFFIC MANAGER AND SWITCH
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
78
No equivalent per-Direction count and threshold for uP destined cells, since
there is only 1 uP port.
All counts represent the number of cells found at the hierarchical level, with the
exception of FreeCnt at the per-Device level. The FreeCnt count value
represents the number of free buffers remaining in the device. The initial value
of FreeCnt is defined by the user.
The congestion algorithm has three possible definitions for CLP:
1) cell CLP, the CLP found in each cell’s header;
2) BOM CLP, the CLP found in the frame BOM cell’s header;
3) OR CLP, the running OR of all received user cell’s CLPs since the BOM
of a frame. Non-user cells do not affect the state of the running OR CLP.
Depending on the VC configuration, anyone of these three definitions can be
used to increment a congestion count, or to select a threshold when comparing
to a count.
When the queue engine receives a cell, the congestion control will apply the
discard rules at each hierarchical level. Only when a cell has passed through
each hierarchical level without being discarded will it be permitted entry into the
queue.
Setting the Max threshold to zero on any given hierarchical level will effectively
disable congestion discards at that hierarchical level. Exception to this rule is the
VcMaxThrsh, which will always have the 8k-1 limit. The xxxCLP0Thrsh
thresholds must always be set greater than or equal to the xxxCLP1Thrsh
thresholds.
There are several error flags set whenever a non-zero maximum threshold is
exceeded. Table 9 correlates the interrupts and context record identification
parameters to the corresponding maximum threshold.
Table 9
- Congestion Error Flags
Threshold
Interrupt
Identification
VcMaxThrsh
QVcMaxThrshErr
(Maskable on per-VC
basis)
VcMaxThrshErrID
ClassMaxThrsh
QClassMaxThrshErr
ClassMaxThrshErrID
ClassMaxThrshErrPortID
PortMaxThrsh
QPortMaxThrshErr
PortMaxThrshErrID