Instruction level test methodology for CPU core software-based self-testing

TIS1 [1] is an instruction level methodology for CPU core self-testing that enhances instruction set of a CPU with test instructions. Since the functionality of test instructions is the same as the NOP instruction, NOP instructions can be replaced with test instructions so that online testing can be done with no performance penalty. TIS tests different parts of the CPU and detects stuck-at faults. This method can be employed in offline and online testing of all kinds of processors. Hardware-oriented implementation of TIS is proposed previously [1] that tests just the combinational units of the processor. Contributions of this paper are first, a software-based approach that reduces the hardware overhead to a reasonable size and second, testing the sequential parts of the processor besides the combinational parts. Both hardware and software oriented approaches are implemented on a pipelined CPU core and their area overheads are compared. To demonstrate the appropriateness of the TIS test technique, several programs are executed and fault coverage results are presented.