3.1.1. Synchronization Register Chains
- The registers in the chain are all clocked by the same clock or phase-related clocks.
- The first register in the chain is driven asynchronously or from an unrelated clock domain.
- Each register fans out to only one register, except the last register in the chain.
The timing slack available in the register-to-register paths of the synchronizer allows a metastable signal to settle, and is referred to as the available settling time. The available settling time in the MTBF calculation for a synchronizer is the sum of the output timing slacks for each register in the chain. Adding available settling time with additional synchronization registers improves the metastability MTBF.