// SPDX-License-Identifier: MIT
`timescale 1ns/1ps
module tb;
  reg clk = 0, reset = 1, request = 0;
  reg release_slot = 1, debug_request = 1;
  reg [3:0] length = 0;
  wire accepted, debug_accepted, full, empty, impossible;
  wire [1:0] occupancy;
  reg [31:0] state;
  integer seed = 1, directed = 0;
  integer short_seen = 0, long_seen = 0;
  integer impossible_seen = 0, debug_seen = 0, checked = 0;
  packet_gate dut(clk, reset, request, release_slot, debug_request,
                  length, accepted, debug_accepted, full, empty,
                  impossible, occupancy);
  always #5 clk = !clk;
  task observe;
    #1;
    if (accepted && length <= 7) short_seen = short_seen + 1;
    if (accepted && length == 15) long_seen = long_seen + 1;
    if (impossible) impossible_seen = impossible_seen + 1;
    if (debug_accepted) debug_seen = debug_seen + 1;
    if (!accepted) $fatal(1, "expected admission in empty simultaneous-release setup");
    checked = checked + 1;
    @(posedge clk);
  endtask
  initial begin
    if ($value$plusargs("seed=%d", seed)) begin end
    if ($value$plusargs("directed=%d", directed)) begin end
    state = 32'(seed);
    @(negedge clk);
    reset = 0;
    request = 1;
    for (integer i = 0; i < 16; i = i + 1) begin
      state = 32'd1664525 * state + 32'd1013904223;
      length = 4'(1 + state % 7);
      observe();
      @(negedge clk);
    end
    if (directed) begin
      length = 15;
      observe();
    end
    $display("seed=%0d directed=%0d checked=%0d short=%0d long=%0d impossible=%0d debug=%0d",
             seed, directed, checked, short_seen, long_seen,
             impossible_seen, debug_seen);
    $finish;
  end
endmodule