Design Constraints Working Group

Glossary

Constraints

Design constraints may include high level design goals, lower-level design goals (budgets), detailed specifications about the desired implementation, and descriptions of the desired handling for special cases. A designer may directly specify lower-level constraints, or they may be derived from higher-level constraints. Examples of design constraints are area and power constraints, clock skew, scan chain order, and desired adder architectures.

Budgets and boundary conditions are specific types of design constraints. Assertions are not design constraints, because they describe how a block should be used, rather than how it should be implemented.

Assertions

Assertions may be associated with particular modes of operation, where they only apply when the block is operating in a particular mode.

Budgets

Constraints which have been hierarchically partitioned among a set of blocks in the design. A simple example is power budgets, where each block is assigned a fraction of the overall power constraint for the design. A more complicated example is arrival times and required times on lower level blocks in a design, which are budgets derived from clock cycle time constraints on paths between the blocks. Boundary Conditions

Aspects of the environment around a design or a block, particularly focused on physical and timing aspects of the connections to the pins on the block. For example, arrival times, required times, external driver types, and external loads. Operating Conditions

Apects of the operating environment for a design or a block such as the ambient temperature, the voltage supplied to the design, and the amount of process variation which should be assumed. Operating Environment

The overall environment in which a design or a block is expected to operate, including both the boundary conditions and operating conditions.