Question

Let us assume that processor testing is done by (1)
filling the PC, registers, and data and instruction memories with some values (you
can choose which values), (2) letting a single instruction execute, then (3) reading
the PC, memories, and registers. These values are then examined to determine if
a particular fault is present. Can you design a test (values for PC, memories, and
registers) that would determine if there is a stuck-at-0 fault on this signal?

Answer 1

Solution

For testing for a "stuck-at-0" fault on a wire, we require an instruction that puts that wire to a value of 1 and has a different result if the value on the wire is stuck-at-0:

If this signal is stuck-at-0, an instruction that writes to an odd numbered register will end up writing to the even numbered register.

Therefore if we place a value of 0 in R30 and a value of 1 in R31, & then execute

ADD R31, R30, R30

the value of R31 is supposed to be 0. If bit 0 of the Write Register input to the Registers unit is stuck-at-0, the value is written to R30 instead and R31 will be 1

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