![](http://datasheet.mmic.net.cn/330000/PM7329-BI_datasheet_16444382/PM7329-BI_69.png)
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
55
by assigning a 3-bit logarithmic weight value and a 7-bit sequence number to
each port. The scheduler maintains a 7-bit polling sequence number and
increments it after each scheduler polling cycle. During a scheduler polling cycle
each of the 128 ports is evaluated. The port will be polled if the following
conditions are met:
the port’s transmit data queue is not empty
the n LSB’s of the scheduler poll sequence number match the n LSB’s
of the port’s sequence number (n is equal to the port’s weight). For
ports with a weight of zero, this compare is ignored. For ports with a
weight of one, then only the LSB is compared. For ports with a weight
of seven, then the entire seven bits are compared.
To maintain even distribution of ports within the same weight class, software
must assign sequence numbers to ports evenly across the 128 polling
sequences. This sequence number need only be changed when a port’s weight
is changed or the distribution ports in a weight group becomes significantly
unbalanced due to port deactivations. Sequence numbers and weights may be
modified at any time.
The logarithmic weights are set so that lower speed ports are evaluated less
often relative to higher speed ports. The following formula show relationship
between the 3 bit logarithmic weights (lw) and the assigned relative throughput
weight (rw) in the case where the aggregate throughput of all the ports is greater
than the available bandwidth:
rw = 2
(7-lw)
The maximum polling rate for any given port is dictated by the number of active
ports. In Any-PHY mode, if only one port is active for all 128 ports (port’s
transmit data queue is not empty), the maximum polling rate is governed by the
following formula:
Max. polling rate = f(SYSCLK) / (64 * 2
lw
)
The equivalent equation for UL2M mode is the following:
Max. polling rate = f(SYSCLK) / 2
lw
10.3 Wan Port Scheduler
The WAN port scheduler operates between the queue engine and the multi-
channel WAN port FIFO. The S/UNI-APEX-1K800 WAN port scheduler provides
weighted interleaved round robin scheduling of up to 4 WAN ports. The dynamic
range of the weights is 8 to 1.