题解 | #信号发生器#

参考题解可知题目未给出的信息，其中的cnt只用于产生方波，注意三角波的flag转换时刻，编写代码如下(附上仿真)：

// 方波的周期是20，锯齿波的周期是21，三角波的周期是40，且wave的最大值是20
`timescale 1ns/1ns
module signal_generator(
	input clk,
	input rst_n,
	input [1:0] wave_choise,
	output reg [4:0]wave
	);

reg [4:0]	cnt;
reg			flag;

always@(posedge clk,negedge rst_n)begin
	if(!rst_n)begin
		wave <= 0;
	end
	else begin
		case(wave_choise)
			0:wave <= ((cnt>=9)&&cnt!=19)?20:0;
			1:wave <= wave<=19?wave+1:0;
			2:wave <= flag?wave+1:wave-1;
			default:wave <= 0;
		endcase
	end
end

always@(posedge clk,negedge rst_n)begin
	if(!rst_n)begin
		cnt <= 0;
		flag<= 0;
	end
	else begin
		cnt <= (wave_choise==0)?(cnt==19?0:cnt+1):0;
		// flag<= (wave_choise==2) ? (((wave==1)&&(!flag)) ? 1 : (((wave==19)&&(flag))?0:flag)) : 0;
        //三目运算太长就不如ifelse语句简洁明了
        if (wave_choise==2) begin
            if ((wave==1)&&(!flag)) begin
                flag <= 1;
            end
            if ((wave==19)&&(flag)) begin
                flag <= 0;
            end
        end
        else begin
            flag <= 0;
        end
	end
end

endmodule

`timescale  1ns / 1ps

module tb_signal_generator;

// signal_generator Parameters
parameter PERIOD  = 10;


// signal_generator Inputs
reg   clk                                  = 0 ;
reg   rst_n                                = 0 ;
reg   [1:0]  wave_choise                   = 0 ;

// signal_generator Outputs
wire  [4:0]  wave                          ;


initial
begin
    forever #(PERIOD/2)  clk=~clk;
end

initial
begin
    $dumpfile ("HDL_bit_wave.vcd");
    $dumpvars;
    #(PERIOD*2) rst_n  =  1;
end

signal_generator  u_signal_generator (
    .clk                     ( clk                ),
    .rst_n                   ( rst_n              ),
    .wave_choise             ( wave_choise  [1:0] ),

    .wave                    ( wave         [4:0] )
);

initial
begin
    #(PERIOD*2);
    #(PERIOD*52) wave_choise = 2'b00;
    #(PERIOD*52) wave_choise = 2'b01;
    #(PERIOD*52) wave_choise = 2'b10;
    #(PERIOD*52) wave_choise = 2'b00;
    #(PERIOD*52) wave_choise = 2'b11;
    #(PERIOD*52);
    $finish;
end

endmodule