This problem occurs if you create an ALT2GXB_RECONFIG instance using the Quartus® II software and simulate in the ModelSim® software, and the
write_all inputs to the ALT2GXB_RECONFIG instance are not assigned a high or low value at the start of the simulation. If these signals are not assigned at the time of the first RECONFIG clock edge in the simulation, the
busy output of the ALT2GXB_RECONFIG instance stays at the don't care (x) value for the entire simulation time even if a valid value is set later in the simulation.
To avoid this problem, assign default values for the
write_all signals so that they are valid at the first RECONFIG clock edge in the simulation.