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VHDL (VHSIC-HDL, Very High-Speed Integrated Circuit Hardware Description Language) is a hardware description language used in electronic des...

Saturday 2 April 2011

Static Timing Analysis

Static timing analysis verifies circuit timing by “adding up propagation delays along paths between clocked elements in a circuit. It checks the delays along each path against the specified timing constraints for each circuit path and reports any existing timing violations. Static timing analysis tools can determine and report timing statistics such as the total number of paths, delays for each path and the circuit’s most critical paths. As design complexity increases, performing timing analysis manually becomes extremely difficult and sometimes even impossible. With increasing popularity of HDL based design methodologies, static timing analysis becomes increasingly popular among digital logic designers. To summarize, both static and dynamic timing analysis methods offer tradeoffs. One is not a replacement for the other. However, the static timing analysis method offers more complete coverage, little overhead, and the ability to report errors in terms of the design schematic.

1.It resembles manual analysis methods.
2. It is path oriented and finds all setup and hold violations.
3. It does not require stimulus or functional models.
4. It is faster than simulation. (for the same amount of coverage).

1. It can report false errors.
2. It cannot detect timing errors related to logical operation.

Static timing analysis is similar to manual analysis process, except that it is automated. This allows the design to be analyzed much faster. This makes it possible for a designer to experiment with different synthesis options and constraints in a short time. This method is also complete because it traces and evaluates all paths in a design, not just those exercised by test stimulus.

Because static timing analysis does not perform logic simulation, test stimulus and functional models are not required. This makes static analysis available earlier since development time for stimulus and models are not required.

The modeling requirements for a static analysis tool are relatively simple. However, timing information for each component in the design is required and the designer must specify waveform information about the input data and clock signals the design uses. The component timing information can be found in parts libraries or data books. Such timing information typically include: pin-to-pin delays, setup, hold time specifications and signal inversion information, and clock frequency constraints. Clock and data waveforms are a normal requirement of the design process, and do not require additional development time.

The major drawback of a static timing analysis tool is that it reports false errors. By checking all possible paths in a design, static timing analysis ensures that all possible setup and hold violations in the circuit have been found. However, the potential to detect some false errors exists since circuit behavior is not considered during the analysis. Static analysis tools cannot detect timing errors related to logical operation. Because static timing analysis does not perform functional testing, it cannot detect timing errors, such as race conditions, that are based on the logical operation of the circuit.

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