On-line testing of statically and dynamically scheduled synthesized systems

Most digital systems at some time during use have areas (modules) that are "dead" in the sense that they do not contain valid data, i.e., the data that was processed or generated by that area has been passed on to a subsequent stage and will not be required (read) again. In a synthesized system, where the flow of data is determined explicitly by an on-chip (synthesized) controller, the question of which areas will be dead or not (and when) is known in advance. There are areas and times when the "use" is data-dependent, but then the use is known to the controller at that time. This deadtime can be exploited to run a test pattern (either complete or in part) through the unused area, thereby giving the ability to continuously monitor the "health" of the overall system with very little (sometimes zero) impact on the processing capability. This has obvious applications in situations where reliability is a concern. There exist systems where an area is so heavily used that it is impossible to perform any testing at a serious rate; in this case the area may either be partially tested (or tested at a lower rate) or the processing of "reap" data periodically halted to anew a more thorough test to take place with concomitant throughput degradation. This paper describes a behavioral synthesis system that can detect and exploit dead areas for automatic testing. Pertinent aspects of the controller are described, and a number of dead area statistics (including "test throughput") generated from real designs are reported.