what is metastability



Metastability is an unknown state it is neither Zero nor One.Metastability happens for the design systems violating setup or hole time requirements. Setup time is a requirement , that the data has to be stable before the clock-edge and hold time is a requirement , that the data has to be stable after the clock-edge. The potential violation of the setup and hold violation can happen when the data is purely asynchronous and clocked synchronously.
Steps to prevent Metastability.
1. Using proper synchronizers(two-stage or three stage), as soon as the data is coming from the asynchronous domain. Using Synchronizers, recovers from the metastable event.
2. Use synchronizers between cross-clocking domains to reduce the possibility from metastability.
3. Using Faster flip-flops (which has narrower Metastable Window).




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