Shift4

Build a 4-bit shift register (right shift), with asynchronous reset, synchronous load, and enable.

• areset: Resets shift register to zero.
• load: Loads shift register with data[3:0] instead of shifting.
• ena: Shift right (q[3] becomes zero, q[0] is shifted out and disappears).
• q: The contents of the shift register.

If both the load and ena inputs are asserted (1), the load input has higher priority.

module top_module(
    input clk,
    input areset,  // async active-high reset to zero
    input load,
    input ena,
    input [3:0] data,
    output reg [3:0] q); 

    always @(posedge clk or posedge areset) begin
        if(areset) 
            q <= 0;
        else begin
            case({ena,load})
                2'b00:q <= q;
                2'b01:q <= data;
                2'b10:q <= q >> 1;
                2'b11:q <= data;
            endcase
    	end
    end
endmodule