说明： quarter ii调用modelsim，在fpga仿真时，为了能减少器件本身对时序的影响，我们一般采用第三方的仿真软件如MODELSIM来验证时序的正确性 (quarter ii call modelsim, in fpga simulation, in order to reduce the impact of the timing device itself, we generally use third parties to verify the simulation software, such as timing correctness MODELSIM)
