Wrapper design for the reuse of a bus, network-on-chip, or other functional interconnect as test access mechanism

Abstract

A new core test wrapper design approach is proposed which transports streaming test data, for example scan test patterns, into and out of an embedded core exclusively via (some of) its functional data ports. The latter are typically based on standardised protocols such as AXI, DTL, and OCP. The new wrapper design allows a functional interconnect, such as an on-chip bus or network-on-chip (NOC) to transport test data to embedded cores, and hence eliminates the need for a conventional dedicated test access mechanism (TAM), such as a TestRail or test bus. The approach leaves both the tester, as well as the embedded core and its test unchanged, while the functional interconnect can handle the test data transport as a regular data application. The functional interconnect is required to offer guaranteed throughput and zero latency variation, a service that is available in many buses and networks. For 672 example cases based on the ITC'02 System-on-Chip (SOC) Test Benchmarks, the new approach in comparison with the conventional approach shows an average wrapper area increase of 14.5%, which is negligible at the SOC level, especially since the dedicated TAM can be eliminated. Futhermore, the new approach decreases the core test length by 3.8% on average.