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What is clock to output delay?
The minimum time required to obtain a valid output at an output pin that is fed by a register after a clock signal transition on an input pin that clocks the register. This time always represents an external pin-to-pin delay.
What is the usage of timing constraints?
Timing constraints are used to specify the timing characteristics of the design. Timing constraints may affect all internal timing interconnections, delays through logic and LUTs and between flip-flops or registers. Timing constraints can be either global or path-specific.
How to constrain timing paths in a clock design?
Defining the clock in a single-clock design constrains all timing paths between registers for a single cycle setup time analysis. Assume the clock in our design is having a time period of 5ns, so we will define a clock with 5ns time period and specify clock port in the design. Note: Unit of time is 1ns in this example.
Why do we need to constrain the virtual clock?
The answer is virtual clock. The virtual clock is a clock that is not connected to any port or pin within the current design but instead serves as a reference for input or output delays. Now constrain our design with respect to this virtual clock. But you may think, why we are discussing this!
How does constraining timing paths in synthesis work?
To constrain all the input paths in our design for setup time, in addition to the clock, we must provide the latest arrival time of the data at the input ports relative to the launching flip-flop’s clock edge (the time delay is called the input delay).
Is the minimum output delay equal to the minimal hold slack?
The minimum output delay is equal to the minimal hold slack. The minimal hold slack is calculated in the following steps: Because the data in this example is launched at the rising edge of the clock the next time the data changes is after one clock period T after tLAUNCH.