Embedded Instrumentation Integration Using Ieee Nexus 5001 and 1149.7 Neal Stollon, Hdl Dynamics

New capabilities for improving embedded control and visibility for chip level analysis and design for debug logic and interfaces to an IC are needed to enable real time functional control, test, and observation of embedded and otherwise not easily accessible operational features [1]. IEEE 5001, also known as Nexus provides a standard method and architecture for embedded instrument interfaces. New debug and instrumentation capabilities, being introduced by Nexus working groups, include support for IEEE 1149.7, which defines the next generation for (JTAG) Debug and Test Control [2]. Given a need for embedded instrumentation, the advantages of adopting standards based solutions are compelling. In addition to reducing the design times required for the instrumentation interface, standards based solutions provide consistency of features and have support from a variety of tools venders. As an example, over half dozen tools vendors support a range of Nexus solutions today. Instrumentation based debug tools have evolved from the earliest days of processor application to provide powerful and compact methods of hardware and software analysis. The most widely used instrumentation interface today is IEEE 1149.1 or JTAG, which is provides a test interface in the majority of digital ICs. JTAG provides a simple and well understood interface supported by many embedded systems tools vendors. JTAG, as IC and board level test interface, has limitations when used as an instrumentation interface. Since JTAG has a single bidirectional serial channel (figure 1), bandwidth is limited; which for communication intensive instrumentation applications such as tracing of embedded signals, can be a serious limitation. Similarly the serial nature of JTAG limits the number of JTAG based instruments that it can practically communicate with, which is a performance limitation barrier for multi-core designs at the SoC or board level. The simplicity of the JTAG interface similarly presents a significant performance limitation in many instrumentation applications. JTAG, as a relatively simple state controlled interface, lacks any native features for security, power management, and other factors important to modern SoC. Despite these limitations, JTAG has remained the leading instrumentation interface, in part due to a lack of alternatives that also support more mainstream test functions.