题解 | #移位运算与乘法#

分三段写更为直观

`timescale 1ns/1ns
module multi_sel(
input [7:0]d ,
input clk,
input rst,
output reg input_grant,
output reg [10:0]out
);
//*************code***********//

	reg [1:0] cnt_4;
	reg [7:0] d_reg;
	
	always @ (posedge clk or negedge rst) begin
		if (!rst)
			cnt_4 <= 2'd0;
		else if (cnt_4 == 2'd3)
			cnt_4 <= 2'd0;
		else 
			cnt_4 <= cnt_4 + 1;
	end
	
	
	always @ (posedge clk or negedge rst) begin
		if (!rst) begin
			d_reg <= 0;
			input_grant <= 1'b0;
		end 
		else if (cnt_4 == 2'd0) begin
			d_reg <= d;
			input_grant <= 1'b1;
		end
		else begin
			d_reg <= d_reg;
			input_grant <= 1'b0;
		end
	end
	
	always @ (posedge clk or negedge rst) begin
		if (!rst) 
			out <= 0;
		else if (cnt_4 == 2'd0)
			out <= d;
		else if (cnt_4 == 2'd1)
			out <= (d_reg<<2) - d_reg;
		else if (cnt_4 == 2'd2)
			out <= (d_reg<<3) - d_reg;
		else if (cnt_4 == 2'd3)
			out <= (d_reg<<3);
		else
			out <= 0;
	end
	

//*************code***********//
endmodule