A system for outputting test data from cores to one communication interface. The system includes shared memories corresponding to the cores. Each shared memory includes a ring buffer and an array of slots. Each core generates a diagnostic message, and stores the generated diagnostic message in a select memory region of the ring buffer corresponding to a first empty slot of the array of slots. A selected core finds a first diagnostic message among diagnostic messages stored in the shared memories, and outputs the first diagnostic message to a personal computer through the communication interface.