get the most out of formal analysis, one thing that can be done is to highly
parameterize a design. Some Cadence guidelines for parameterization
include the following:
? Pass down all parameters
from top to bottom.
? Vectors that can affect size
and diameter, which impacts complexity, should be
? Every parameter should be
orthogonal to other parameters.
? Compute dependent parameters
as functions of independent parameters.
? Include system-wide/protocol
requirements as parameters even if they would never change between reuses of
example, if every packet of data should be no greater than 256 bytes or data
should be divided up into bursts of 64 bytes or less, then 256 and 64 should be
parameters, not hard-coded numbers.
? Parameterize number of
interfaces to replicated blocks.
For example, for an arbiter, use N arbitration interfaces instead of a fixed
? Design logic so that it
works for any width of bus.
For example, for a data bus (8, 16, 32-bits, and so on), define a parameterized
HDL parameters is not the only way to “parameterize” a design, defines can also
be used. I use defines for global
constants that are not changed on a module by module instantiation. I use parameters when a module’s constants
need to be changed on an instance by instance basis. The goal being that a top-level parameter can
be changed in one spot and the entire design is updated accordingly because the
lower level parameters are orthogonal.
a design often times allows one to easily shrink a design down enough such that
the properties in the design can be proved by a formal analysis tool like IFV.
highly parameterized design often times comes with requirements of using some
of the constructs introduced to Verilog in Verilog 2001 including generates,
indexed part-selects, and multi-dimensional wires. Also, one tends to write with a very
different style. The resulting code
sometimes ends up looking more like a program than a hardware description. This style is not always the easiest to read
for people who are used to other styles that make gates easier to “see”. Also, you may find your occasional tool bug
with Verilog 2001 constructs since they are not as widely used.
sometimes get to be very wide because there isn’t an easy way to change the
number of input vectors to a module. For
instance, you may need a mux module that has a parameterized number of
inputs. This would lead to an interface
definition like the following:
highly parameterized design is not just good from formal analysis, it also
leads to a more flexible and reusable design.
These benefits go well beyond formal analysis.