// snippet
t.addr = 32'h1003; t.size = 3'd2;     // plant the suspect values
if (!t.randomize(null)) $display("0x1003 with size 2 breaks a constraint");

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class axi_txn;
  rand bit [31:0] addr;
  rand bit [2:0]  size;
  constraint align_c { addr % (32'd1 << size) == 0; }
  constraint size_c  { size inside {[3'd2:3'd3]}; }
endclass

module tb_pin_check;
  axi_txn t = new();
  // Check-only: pin every rand field to the suspect values. The call can only
  // succeed if those exact values satisfy every active constraint.
  function automatic bit legal(bit [31:0] a, bit [2:0] s);
    axi_txn probe = new();
    return probe.randomize() with { addr == a; size == s; };
  endfunction
  initial begin
    bit r1, r2, r3;
    r1 = legal(32'h1004, 3'd2);   // 4-byte aligned, 4-byte beats
    r2 = legal(32'h1003, 3'd2);   // not 4-byte aligned
    r3 = legal(32'h1004, 3'd3);   // 8-byte beats need an 8-byte boundary
    $display("addr 1004 size 2: %0d   addr 1003 size 2: %0d   addr 1004 size 3: %0d", r1, r2, r3);
    if (!(r1 && !r2 && !r3)) $fatal(1, "FAIL: a pinned check gave the wrong verdict");
    $display("PASS: pinning every field with an inline with gave the three verdicts by hand");
    $finish;
  end
endmodule

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class eth_frame;
  rand bit [13:0] length;
  constraint legal_c { length inside {[64:1518]}; }
endclass

module top;
  initial begin
    eth_frame f = new();
    // Wants a jumbo frame. Inline ANDs with legal_c, so this is empty.
    if (!f.randomize() with { length == 9000; })
      $display("inline length 9000 vs class range: no solution");
    else $fatal(1, "FAIL: length 9000 should contradict legal_c");
    $display("PASS: the inline jumbo request failed as expected");
    $finish;
    // Fix 1: soften the class default, then the hard inline wins.
    // Fix 2: f.legal_c.constraint_mode(0) around this one call.
    // Fix 3: subclass eth_frame with a jumbo constraint.
  end
endmodule

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// minimal_repro: 3 constraints, 1 state value, no methodology code.
class repro;
  rand bit [31:0] addr;
  rand bit [2:0]  size;
  constraint align_c { addr % (1 << size) == 0; }
  constraint hot_c   { addr inside {[32'h1001:32'h1003]}; }
  constraint size_c  { size >= 3'd2; }
endclass

module top;
  initial begin
    repro r = new();
    // UNSAT: size>=2 needs addr divisible by 4, but the hot window
    // holds no multiple of 4. Three constraints, zero solutions.
    if (!r.randomize()) $display("PASS: repro shows UNSAT as analyzed");
    else $fatal(1, "FAIL: solved: addr=%h size=%0d", r.addr, r.size);
    $finish;
  end
endmodule