E203 bypass buffer

如果fifo中没有数据，且有输入，则是bypass fifo，同周期内直接把输入数据转到输出数据。如果fifo中有数据，则读取fifo，成为普通的同步fifo。

module sirv_gnrl_bypbuf # (
  parameter DP = 8,
  parameter DW = 32
) (
  input           i_vld,
  output          i_rdy,
  input  [DW-1:0] i_dat,

  output          o_vld,
  input           o_rdy,
  output [DW-1:0] o_dat,

  input           clk,
  input           rst_n
);

  wire          fifo_i_vld;
  wire          fifo_i_rdy;
  wire [DW-1:0] fifo_i_dat;

  wire          fifo_o_vld;
  wire          fifo_o_rdy;
  wire [DW-1:0] fifo_o_dat;

  sirv_gnrl_fifo # (
       .DP(DP),
       .DW(DW),
       .CUT_READY(1)
  ) u_bypbuf_fifo(
    .i_vld   (fifo_i_vld),
    .i_rdy   (fifo_i_rdy),
    .i_dat   (fifo_i_dat),
    .o_vld   (fifo_o_vld),
    .o_rdy   (fifo_o_rdy),
    .o_dat   (fifo_o_dat),
    .clk     (clk  ),
    .rst_n   (rst_n)
  );

   // This module is a super-weapon for timing fix,
   // but it is tricky, think it harder when you are reading, or contact Bob Hu

  assign i_rdy = fifo_i_rdy;

  // The FIFO is bypassed when:
  //   * fifo is empty, and o_rdy is high
  wire byp = i_vld & o_rdy & (~fifo_o_vld);

  // FIFO o-ready just use the o_rdy
  assign fifo_o_rdy = o_rdy;

  // The output is valid if FIFO or input have valid
  assign o_vld = fifo_o_vld | i_vld;

  // The output data select the FIFO as high priority
  assign o_dat = fifo_o_vld ? fifo_o_dat : i_dat;

  assign fifo_i_dat  = i_dat;

  // Only pass to FIFO i-valid if FIFO is not bypassed
  assign fifo_i_vld = i_vld & (~byp);

endmodule

module sirv_gnrl_dffs_tb;

   reg  clk=0,rst_n;
   reg  i_vld, o_rdy;
   reg  [31:0] i_dat;

   wire i_rdy, o_vld;
   wire [31:0] o_dat;

   sirv_gnrl_bypbuf  #(.CUT_READY(1),.DP(4),.DW(32)) mybuf(.i_vld(i_vld),.i_rdy(i_rdy),.i_dat(i_dat),.o_vld(o_vld),.o_rdy(o_rdy),.o_dat(o_dat),.clk(clk),.rst_n(rst_n));

   always #10 clk=~clk;

   initial
   begin
	rst_n=1'b1;
	i_vld = 1'b0;
        o_rdy = 1'b0;
	i_dat = 32'h12345678;
	#20
	rst_n=1'b0;
	#80
	rst_n=1'b1;
	#80
	i_vld = 1'b1;
        o_rdy = 1'b1;
	i_dat = 32'h8;
	#20
	i_vld = 1'b1;
        o_rdy = 1'b1;
	i_dat = 32'h12;
	#20
	i_vld = 1'b1;
        o_rdy = 1'b1;
	i_dat = 32'h2;
	#20
	i_vld = 1'b1;
        o_rdy = 1'b1;
	i_dat = 32'h11;
	#20
	i_vld = 1'b1;
        o_rdy = 1'b1;
	i_dat = 32'h13;
	#20
	i_vld = 1'b1;
        o_rdy = 1'b1;
	i_dat = 32'h6;
	#20
	i_vld = 1'b1;
        o_rdy = 1'b1;
	i_dat = 32'h22;
	#20
	i_vld = 1'b1;
        o_rdy = 1'b1;
	i_dat = 32'h99;
	#20
	i_vld = 1'b1;
        o_rdy = 1'b1;
	i_dat = 32'h33;
	#20
	i_vld = 1'b0;
        o_rdy = 1'b1;
	i_dat = 32'h17;
	#20
	i_vld = 1'b1;
        o_rdy = 1'b1;
	i_dat = 32'h3;
        #500 $finish;
   end

   initial
	   $monitor($time,,,"clk=%b,rst_n=%b,i_vld=%b,o_rdy=%b, i_rdy=%b, o_vld=%b,",clk,rst_n,i_vld,o_rdy,i_rdy,o_vld);
   initial
   begin
   	//$dumpfile("dump.vcd");
   	//$dumpvars;
   	$fsdbDumpfile("dump.fsdb");
	$fsdbDumpvars("+all");
   end

   endmodule

用上面的testbench，可以看到是bypass buffer，fifo_o_vld总为0

module sirv_gnrl_dffs_tb;

   reg  clk=0,rst_n;
   reg  i_vld, o_rdy;
   reg  [31:0] i_dat;

   wire i_rdy, o_vld;
   wire [31:0] o_dat;

   sirv_gnrl_bypbuf  #(.CUT_READY(1),.DP(4),.DW(32)) mybuf(.i_vld(i_vld),.i_rdy(i_rdy),.i_dat(i_dat),.o_vld(o_vld),.o_rdy(o_rdy),.o_dat(o_dat),.clk(clk),.rst_n(rst_n));

   always #10 clk=~clk;

   initial
   begin
	rst_n=1'b1;
	i_vld = 1'b0;
        o_rdy = 1'b0;
	i_dat = 32'h12345678;
	#20
	rst_n=1'b0;
	#80
	rst_n=1'b1;
	#80
	i_vld = 1'b1;
        o_rdy = 1'b0;
	i_dat = 32'h8;
	#20
	i_vld = 1'b1;
        o_rdy = 1'b0;
	i_dat = 32'h12;
	#20
	i_vld = 1'b1;
        o_rdy = 1'b1;
	i_dat = 32'h2;
	#20
	i_vld = 1'b1;
        o_rdy = 1'b1;
	i_dat = 32'h11;
	#20
	i_vld = 1'b1;
        o_rdy = 1'b1;
	i_dat = 32'h13;
	#20
	i_vld = 1'b1;
        o_rdy = 1'b1;
	i_dat = 32'h6;
	#20
	i_vld = 1'b1;
        o_rdy = 1'b1;
	i_dat = 32'h22;
	#20
	i_vld = 1'b1;
        o_rdy = 1'b1;
	i_dat = 32'h99;
	#20
	i_vld = 1'b1;
        o_rdy = 1'b1;
	i_dat = 32'h33;
	#20
	i_vld = 1'b0;
        o_rdy = 1'b1;
	i_dat = 32'h17;
	#20
	i_vld = 1'b1;
        o_rdy = 1'b1;
	i_dat = 32'h3;
        #500 $finish;
   end

   initial
	   $monitor($time,,,"clk=%b,rst_n=%b,i_vld=%b,o_rdy=%b, i_rdy=%b, o_vld=%b,",clk,rst_n,i_vld,o_rdy,i_rdy,o_vld);
   initial
   begin
   	//$dumpfile("dump.vcd");
   	//$dumpvars;
   	$fsdbDumpfile("dump.fsdb");
	$fsdbDumpvars("+all");
   end

   endmodule

如果用上面的testbench，则变成普通的buffer，没有bypass