
Nexus (standard)

Nexus or IEEE-ISTO 5001-2003 is a standard debugging interface for embedded systems.
Features.
The IEEE-ISTO 5001-2003 (Nexus) feature set is modeled on today's on-chip debug implementations, most of which are processor-specific. Its goal is to create a rich debug feature set while minimizing the required pin-count and die area, and being both processor- and architecture independent. It also supports multi-core and multi-processor designs. Accordingly, it is comparable to the ARM CoreSight debug architecture.
Physically, IEEE-ISTO 5001-2003 defines a standard set of connectors for connecting the debug tool to the target or system under test. Logically, data is transferred using a packet-based protocol. This protocol can be JTAG (IEEE 1149.1); or, for high-speed systems, an auxiliary port can be used that supports full duplex, higher bandwidth transfers.
Key Nexus functionality involves either JTAG-style request/response interactions, or packets transferred through the debug port, and includes:
A low-level application programming interface (API) is also allowed for, to mask target specifics such as the host connection mechanism (such as an emulator or Calibration-instrument) and processor specific Nexus register details. This API is produced jointly by the tool and semiconductor vendor.
Compliance classes.
IEEE-ISTO 5001-2003 is a scalable standard; there are currently four classes of compliance to the standard, ranging from the basic (JTAG only) Class 1 up to Class 4.