handshake_gate.v

handshake checker and it is used in the design of USB or other material ,it is a simple one on the a

/*module handshake_gate;
    input  a,clk, r, reset;
    output ef;
    wire cob_a, cob_r, a1,a1not, a,anot,r1,r1not,r,rnot,cob1,cob2,cob3,e0;
    begin
        nor(cob_a,~a,reset);
        nor(cob_r,~r,reset);
    d_ff (.d(cob_a),.clk(clk),.q(a1),._q(a1not));
    d_ff  (.d(a1),.clk(clk),.q(a),._q(anot));
    d_ff  (.d(cob_r),.clk(clk),.q(r1),._q(r1not));
    d_ff  (.d(r1),.clk(clk),.q(r),._q(rnot));
    and  (cob1,rnot,anot,r1not);
    and (cob2,rnot,r1,a1not);
    and (cob3,r,a,a1not);
    or  (e0, cob1,cob2, cob3);
    locker final(.reset(reset),.e0(e0),.ef(ef));
end
endmodule; */



module handshake_gate(a,clk,r,reset,ef);
    input  a,clk, r, reset;
    output ef;
    wire cob_a, cob_r, a1,a1not, a,anot,r1,r1not,r,rnot,cob1,cob2,cob3,e0;
   // begin
        nor(cob_a,~a,reset);
        nor(cob_r,~r,reset);
    d_ff  H(.d(cob_a),.clk(clk),.q(a1),._q(a1not));
    d_ff  I(.d(a1),.clk(clk),.q(a),._q(anot));
    d_ff  J(.d(cob_r),.clk(clk),.q(r1),._q(r1not));
    d_ff  K (.d(r1),.clk(clk),.q(r),._q(rnot));
    and  (cob1,rnot,anot,r1not);
    and (cob2,rnot,r1,a1not);
    and (cob3,r,a,a1not);
    or  (e0, cob1,cob2, cob3);
    locker final(.reset(reset),.e0(e0),.ef(ef));
// end
endmodule