In last month's blog entry "An Expert's View on Power
Formats and Methodology", I highlighted a recent interview by Ed Sperling with
Sorin Dobre of Qualcomm, posted on the Low
Power Engineering Community. Amongst other things, Sorin explained how
Qualcomm takes advantage of the hierarchical methodology in the Common Power Format (CPF).
This month, my
good friend and Cadence colleague, Luke Lang, penned his third entry in a
series of methodology articles, Hierarchical
LP Design 3 in his "Everything Low Power" blog in the same on-line community.
When taken with the other two (Hierarchical
LP Design and Hierarchical
LP Design 2) the series adds up to a comprehensive tutorial on both the
value and the "how to" of hierarchical methodology in a power format, and
the tools that support the format.
Luke first covers how macro modeling can
capture power intent for IP blocks. Then he describes the capability to express
power intent top-down, which can set rules abstractly without worrying about
the details of all the power domain crossings lower in the design hierarchy. In
his third entry, he elaborates on the bottom-up approach, and the ability to
integrate the same block, in multiple situations requiring different use of the
block's internal power intent capabilities. Finally he describes how to use
virtual ports and virtual power domains to simplify specification of rules for design
objects that will later appear lower in the hierarchy, as the design
Not all these hierarchical capabilities are truly
unique to CPF. In fact, there is hierarchy support in the IEEE 1801 standard
for soft IP blocks, although it remains limited by Liberty in terms of the
power intent that can be described for a macro IP block. Another big problem is
the inclusion of Unified Power Format (UPF) 1.0 in 1801, which is still the subset of 1801 supported
by most UPF-based low power tools, and has only limited and incomplete semantics in
terms of hierarchy.
So for now, these hierarchical capabilities are unique to the Cadence
CPF-enabled low power solution. However, with our participation in IEEE 1801
and Si2's contribution of the CPF Open
Low Power Methodology to IEEE 1801, we're rapidly progressing towards
making these capabilities available to those who favor UPF too.