`ASSERT_ALWAYS_MSG(data_x_256b, m_clock, reset,
   ((req_select_mon != 0) && (req_info.size === 3'b101) && ($size(req_info.data) >= 256) && ((req_info.opcode === 5'b00000) || (req_info.opcode === 5'b00010)) |-> (!($isunknown(req_info.data[start_addr_bit +: 256]))  || !($stable(req_valid)) )),
   "Valid DATA contain X values for write or write-around operation and size of 256 bits");

`ASSERT_ALWAYS_MSG(data_x_512b, m_clock, reset,
   ((req_select_mon != 0) && (req_info.size === 3'b110) && ($size(req_info.data) == 512) && ((req_info.opcode === 5'b00000) || (req_info.opcode === 5'b00010)) |-> ( !($isunknown(req_info.data[511:0])) || !($stable(req_valid)) )),
   "Valid DATA contain X values for write or write-around operation and size of 512 bits");