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Let us define the RTL interconnects connected to the output of a
datapath nit in the datapath as its output network. A
functional unit with more than one operation or a register with
more than one variable bound to it outputs values of multiple
variables onto its output network in different clock cycles. In
general, the output value has to be routed to only a small portion
of the output network in a given clock cycle. If care is not
taken, many other parts of the network may also experience
switching activity. Many functional units, for example, a
ripple-carry adder, output a lot of glitches before the output
finally settles down to the correct value [46]. These
glitches also contribute significantly to the output network power
consumption.
Fig. 3 shows the percentage of total
interconnect power consumed through SSA for the eight benchmarks
optimized for area and power. For both AO and IUPO circuits, SSA
consumes a significant percentage of total interconnect power,
with the average being 62.6% and 29.2%, respectively, even when
glitches are not taken into account. AO circuits incur a higher
percentage of SSA power in interconnects because their datapath
units are usually heavily shared.
Figure 3:
Percentage of total interconnect power consumed by SSA.
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Next: Motivational example
Up: Observations
Previous: Interconnect power consumption
Lin Zhong
2003-10-11