题解2 | #移位运算与乘法#

将cnt/d_temp/移位运算拆分成多个写

注意：第一次计算d*1 时，out 并不能写为 out <= d_temp ，此时d_temp 是上一拍的值，当cnt = 0 && rst 时才将d存到d_temp 里。

`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 [2:0] cnt;
reg [7:0] d_temp;

always @(posedge clk or negedge rst)
begin
    if (!rst)
        cnt <= 0;
   
    else if (cnt == 3'd3)
        cnt <= 0;

    else 
        cnt <= cnt +1;

end

always @(posedge clk or negedge rst)
begin
    if (!rst)
    begin
        d_temp <= 0;
        input_grant <= 0;
    end

    else if (cnt == 0)
    begin
    d_temp <= d;
    input_grant <= 1;
    end
    
    else
    begin
    d_temp <= d_temp;
    input_grant <= 0;
    end
end

always @(posedge clk or negedge rst)
begin
    if (!rst)
    out <= 0;

    else
        case(cnt)
        3'd0: out <= d;  
        3'd1: out <= (d_temp << 2) - d_temp;
        3'd2: out <= (d_temp << 3) - d_temp;
        3'd3: out <= d_temp << 3;
        default: out <= 0;
        endcase
end



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