'timescale 1ns/1ps //定义 时间单位/时间精度

parameter TIME_PERIOD = 10;
reg clock;
initial
begin
clock = 0;//初始化clock为0
forever
   # (TIME_PERIOD/2) clock = ~clock; 
end

parameter TIME_PERIOD = 10;
reg clock;
initial
clock = 0;//初始化clock为0
always
# (TIME_PERIOD/2) clock = ~clock;

parameter HI_TIME = 5,
    LO_TIME = 10;
reg clock;
always
begin
# HI_TIME clock = 0;
# LO_TIME clock = 1;
end

parameter PULSE_COUNT = 4,
    TIME_PERIOD = 10;
reg clock;
initial
begin
clock = 0;//初始化clock为0
repeat (2*PULSE_COUNT)
   # (TIME_PERIOD/2) clock = ~clock; 
end

parameter HI_TIME = 5,
    LO_TIME = 10,
    PHASE_SHIFT = 2;
reg   absolute_clock;
wire derived_clock;
always
begin
# HI_TIME absolute_clock = 0;
# LO_TIME absolute_clock = 1;
end

assign # PHASE_SHIFT derived_clock = absolute_clock;