题解 | #移位运算与乘法#

/*
此题要注意d值在cnt=0时进入reg_d，即d=128时的波形比较特别

*/

`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;
reg [7:0] reg_d;

always@(posedge clk or negedge rst) begin
    if(!rst) begin
        cnt <= 0;
    end
    else if(cnt == 2'b11) begin
        cnt <= 0;
    end
    else begin
        cnt <= cnt + 1 ;
    end
end

always@(posedge clk or negedge rst) begin
    if(!rst) begin
        reg_d       <= 0;
        out         <= 0;
        input_grant <= 0 ;
    end
    else begin
        case(cnt) 
            2'b00:begin
                reg_d       <= d;
                out         <= d;
                input_grant <= 1'b1 ;
            end
            2'b01:begin
                out         <= (reg_d<<2)-reg_d;
                input_grant <= 0 ;
            end
            2'b10:begin
                out         <= (reg_d<<3)-reg_d;
                input_grant <= 0 ;
            end
            2'b11:begin
                out         <= reg_d<<3;
                input_grant <= 0 ;
            end
            default : begin
                out <= 11'b0;
                input_grant <= 0 ;
            end
            
        endcase
    end

end


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