AR# 5057: 4.2i Foundation Timing Simulator - Metastable operation not accurately simulated (undefined state persists)
AR# 5057
4.2i Foundation Timing Simulator - Metastable operation not accurately simulated (undefined state persists)
Description
Keywords: Timing, Simulator, metastable, Foundation, metastability, undefined, setup, hold
Urgency: Standard
General Description: When a metastable operation occurs in timing simulation in the Foundation simulator, the simulator does not go stable until either a clear, a preset, or the next clock cycle is encountered.
Solution
If a setup or hold time parameter is violated in simulation, the FF/latch output will not be defined.
If an actual device register goes into a metastable state, it will probably recover well within 1 ns and the design process will continue. This process is outlined in the Xilinx Application Note "Metastable Recovery" (Xilinx XAPP094).