![]() Minimum or maximum delay path. A path that must meet a delay constraint that you explicitly specify as a time value.The tor expert bundle contains the tor and pluggable transports binaries, bridge strings, and geoip data used in Tor Browser.Multicycle path. A path designed to take more than one clock cycle from launch to capture.False path. A path that is never sensitized due to the logic configuration, expected data sequence, or operating mode.Otherwise, the tool might incorrectly report those paths as having timing violations.Īn STA tool may let you specify the following types of exceptions: If certain paths are not intended to operate according to the default setup and hold behavior assumed by the STA tool, you need to specify those paths as timing exceptions. A hold violation can occur if the clock path has a long delay. For this hold check, the tool considers the shortest possible delay along the data path and the longest possible delay along the clock path between FF1 and FF2. This check ensures that the data already existing at the input of FF2 remains stable long enough after the clock edge that captures data for the previous cycle. ![]() When the tool performs a hold check, it verifies that the data launched from FF1 reaches FF2 no sooner than the capture clock edge for the previous clock cycle. For this setup check, the tool considers the longest possible delay along the data path and the shortest possible delay along the clock path between FF1 and FF2. If the data path delay is too long, it is reported as a timing violation. Therefore, when the tool performs a setup check, it verifies that the data launched from FF1 reaches FF2 within one clock cycle, and arrives at least 1.0 time unit before the data gets captured by the next clock edge at FF2. The time unit size, such as ns or ps, is specified in the logic library.īy default, the tool assumes that signals are propagated through each data path in one clock cycle. The clock period is defined in the tool to be 10 time units. The following example shows how STA checks setup and hold constraints for a flip-flop:įor this example, assume that the flip-flops are defined in the logic library to have a minimum setup time of 1.0 time units and a minimum hold time of 0.0 time units. This constraint enforces a minimum delay on the data path relative to the clock edge. A hold constraint specifies how much time is necessary for data to be stable at the input of a sequential device after the clock edge that captures the data in the device.This constraint enforces a maximum delay on the data path relative to the clock edge. A setup constraint specifies how much time is necessary for data to be available at the input of a sequential device before the clock edge that captures the data in the device.STA then checks for violations of timing constraints, such as setup and hold constraints: This delay is caused by the parasitic capacitance of the interconnection between the two cells, combined with net resistance and the limited drive strength of the cell driving the net. Net delay is the amount of delay from the output of a cell to the input of the next cell in a timing path. From these table entries, the tool calculates each cell delay. Typically, a delay table lists the amount of delay as a function of one or more variables, such as input transition time and output load capacitance. ![]() In the absence of back-annotated delay information from an SDF file, the tool calculates the cell delay from delay tables provided in the logic library for the cell. The total delay of a path is the sum of all cell and net delays in the path.Ĭell delay is the amount of delay from input to output of a logic gate in a path. After breaking down a design into a set of timing paths, an STA tool calculates the delay along each path.
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