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<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8">
  </head>
  <body>
    <script>

    function Memory(arrayBuffer) {
      this.arrayBuffer = arrayBuffer;
      this.length      = arrayBuffer.byteLength;
      this.u8          = new Uint8Array(arrayBuffer);
    }

    Memory.prototype = {
      readU32 : function (offset) {
        return ((this.u8[offset] << 24) | (this.u8[offset+1] << 16) | (this.u8[offset+2] << 8) | this.u8[offset+3])>>>0;
      },

     write32 : function (offset, value) {
        this.u8[offset  ] = value >> 24;
        this.u8[offset+1] = value >> 16;
        this.u8[offset+2] = value >>  8;
        this.u8[offset+3] = value;
      }
    };

    function Device(mem, rangeStart) {
      this.mem        = mem;
      this.rangeStart = rangeStart;
    }

    Device.prototype = {
      read32 : function (address) {
        var ea = address - this.rangeStart;
        return this.mem.readU32(ea);
      },

      write32 : function (address, value) {
        var ea = address - this.rangeStart;
        this.mem.write32(ea, value);
      }
    };

    var mem = new Memory(new ArrayBuffer(0x2000)); // NB doesn't repro with less than 0x2000?
    var dev = new Device(mem, 0xa0000000);

    // With this value, the test fails 100% of the time after 130-134 iterations.
    var magic_value = 0xaaaaaaaa;

    // NB with 31 bit value, e.g 0x04123456,
    // the test fails about 25% of the time after 132 iterations.
    //var magic_value = 0x0aaaaaaa;

    function test(addr, val, i) {
      dev.write32(addr, val);

      var actual = dev.read32(addr);
      if (actual!== magic_value) {
        var o = addr - dev.rangeStart;
        alert('test failed after ' + i + ' iterations.\n' +
          'Expecting ' + magic_value.toString(16) + ' but got ' + actual.toString(16) + '\n' +
          'Values: ' + dev.mem.u8[o+0].toString(16) + ' ' +
                       dev.mem.u8[o+1].toString(16) + ' ' +
                       dev.mem.u8[o+2].toString(16) + ' ' +
                       dev.mem.u8[o+2].toString(16)
      );
        return false;
      }
      return true;
    }

    var addr = 0xa0000000;

    for(var i = 0; i < 100000; ++i) {
      if (!test(addr, magic_value, i)) {
        break;
      }
    }

    </script>

  </body>
</html>