Hierarchical test access architecture for embedded cores in an integrated circuit

The rapid emergence of reusable core-based designs, in the last few years, poses new challenges to the IEEE test access standard 1149.1. Due to widespread industrial acceptance of 1149.1 standard, ICs are now expected to be 1149.1-compliant. At the same time, a typical IC, like the TMS470 microcontroller manufactured by TI, often contains multiple cores with built-in 1149.1 compliant Test Access Port (TAP), as well as significant amounts of non-core logic, which does not have any built-in test access mechanism. In this paper, we present a new TAP design that enables systematic integration of TAP'ed cores with non-TAP'ed logic, and makes the total IC 1149.1 compliant, at the same time. This TAP design, designated Hierarchical Test Access Port (HTAP), has exactly the same I/O pin specifications as an 1149.1-compliant TAP, and can either serve as an 1149.1-compliant TAP, or act as an arbitrator between existing TAPs in the Embedded cores. Behavior of the HTAP-whether to act as a TAP or as an arbitrator of TAPs-is controlled via the TMS input pin.