Shadow checker (SC): A low-cost hardware scheme for online detection of faults in small memory structures of a microprocessor

At various stages of a product life, faults arise from different sources. During product bring up, logic errors are dominant. During production, manufacturing defects are main concerns while during operation, the concern shifts to aging defects. No matter what the source is, debugging such defects may permit logic, circuit or physical design changes to eliminate them in future. Within a processor chip, there are three broad categories of structures, namely the large memory structures such as caches, small memory structures such as reorder buffer, issue queue, and load-store buffers and the data-path. Most control functions and data steering operations are based on small memory structures and they are hard to debug. In this paper, we propose a lightweight hardware scheme, called shadow checker to detect faults in these critical units. The entries in these units are tested by means of a shadow entry that mimics intended operation. A mismatch traps an error. The shadow checker shadows an entry for a few thousand cycles before moving on to shadow another. This scheme can be employed to test chips during silicon debug, manufacturing test as well as during regular operation. We ran experiments on 13 SPEC2000 benchmarks and found that our scheme detects 100% of inserted faults.