rptr_empty.v

Simulation and Synthesis Techniques for synchronous FIFO Design

module rptr_empty #(parameter ADDRSIZE = 4)
  (output reg                rempty,
   output     [ADDRSIZE-1:0] raddr,
   output reg [ADDRSIZE  :0] rptr,
   input      [ADDRSIZE  :0] rq2_wptr,
   input                     rinc, rclk, rrst_n);
  reg  [ADDRSIZE:0] rbin;
  wire [ADDRSIZE:0] rgraynext, rbinnext;
  //-------------------
  // GRAYSTYLE2 pointer
  //-------------------
  always @(posedge rclk or negedge rrst_n)
    if (!rrst_n) {rbin, rptr} <= 0;
    else         {rbin, rptr} <= {rbinnext, rgraynext};
  // Memory read-address pointer (okay to use binary to address memory)
  assign raddr     = rbin[ADDRSIZE-1:0];
  assign rbinnext  = rbin + (rinc & ~rempty);
  assign rgraynext = (rbinnext>>1) ^ rbinnext;
  //---------------------------------------------------------------
  // FIFO empty when the next rptr == synchronized wptr or on reset
  //---------------------------------------------------------------
  assign rempty_val = (rgraynext == rq2_wptr);
  always @(posedge rclk or negedge rrst_n)
    if (!rrst_n) rempty <= 1'b1;
    else         rempty <= rempty_val;
endmodule