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NEXUS TOOLS
Ashling's Emulators and Debuggers for NEXUST-standard Microprocessor Debugging
Ashling is an active contributor to the NEXUS 5001T Forum, which has defined and published a Standard Global Embedded Processor Debug Interface for use in complex, high-speed On-Chip Debug implementations. NEXUS technology provides a global, scalable standard for debugging and calibrating complex high-speed RISC embedded microprocessors.
Introducing NEXUS
On-Chip Debugging
The NEXUS debug hardware interface
NEXUS compliance classes
Latest developments on the NEXUS Standard
For more information.
The NEXUS (IEEE-ISTO 5001T-1999) Standard has been created to provide a standard debug interface for embedded control applications. This interface is used to connect tools to an embedded system for:
- Run-time control (debugging)
- Code execution trace capture and Data access trace capture
- Calibration (Data access on-the-fly)
- Logic Analysis Rapid-prototyping
NEXUS specifies an open, global, general-purpose interface for development, debugging and optimization of automotive systems. Originally termed the Global Embedded Processor Debug Interface Standard Consortium, the NEXUS 5001T Forum is now a program of the IEEE Industry Standards and Technology Organization (IEEE-ISTO). The group's objectives are the development, dissemination, and implementation of a global interface standard for debugging of embedded processors.
As an active participant in the NexusT 5001 Forum, Ashling has worked closely with Freescale (Motorola) Semiconductors and the other forum members to produce the first Emulator and Real-time Trace system for Freescale (Motorola)'s MPC56x "Spanish Oak" automotive microprocessor family. The MPC565 is the industry's first device to feature a full Class 3 Nexus debug and calibration port. This means that external development, debug and calibration hardware can access the microprocessor "on-the-fly" without intrusion on program execution, to monitor or change variables, trace program flow or alter calibration tables, through a debug port defined by the NEXUS global standard.
The standard builds on the experience of a wide range of semiconductor vendors, development system suppliers and embedded systems design engineers (see www.ieee-isto.org/Nexus5001/membership.html for a full list of Nexus 5001 ForumT members). The NEXUS consortium now includes more than 30 companies, spanning the semiconductor, development-tools and automotive-electronics industries. Although the initial focus of the consortium was on the stringent requirements of automotive powertrain applications, the overall goal is to see the general-purpose standard applied and adopted all industries that will benefit from this standard interface, such as data communications and computer peripherals, wireless systems and other embedded control applications.
On-chip debugging support logic is a mandatory silicon component within complex high-speed RISC microprocessors; without such support logic it would be impossible or prohibitively expensive to implement debugging tools capable of supporting increasing clock speeds. Use of application-specific or customer-specific Systems-On-a-Chip (SOCs), some with multiple processors, means that a uniform, reliable debugging interface is essential to reduce the task of redesigning the microprocessor emulator for each individual SoC design. Meeting a short window of sales opportunity for a new embedded product requires fast and efficient product development. Since debug and verification makes up a significant part of the development cycle, an effective debug mechanism is vital.
NEXUS specifies the functions and interfaces (not the implementation) of the On-Chip Debug module.
The NEXUS debug hardware interface
The IEEE-ISTO 5001T-1999 (NEXUS) standard is designed to be processor and architecture independent and to support multi-core or multi-processor designs. It defines a standard set of connectors for connecting the debug tool to the target (the system-under-test. Data is transferred using a packet protocol. The physical interface is usually IEEE JTAG 1149.1; for high speed systems an auxiliary port can be used which supports full duplex, higher bandwidth transfers.
IEEE-ISTO 5001T-1999 (NEXUS) is a scalable standard, with (currently) four classes of compliance to the standard, ranging from the basic (JTAG-only) Class 1 up to Class 4.
NEXUS Debug Class Characteristics
| IEEE-ISTO 5001T-1999 Class | Class 1 | Class 2 | Class 3 | Class 4 |
| Trace features | Trace not supported | Adds ownership trace and program trace via Auxiliary ports | Adds data write trace and read/write memory on the fly via Auxiliary ports | Allows tracing to be triggered by a watchpoint via Auxiliary ports |
| Debug communication method | Half-duplex communication (Limited bandwidth) | Communication may be full duplex using Auxiliary port (higher bandwidth) | Communication may be full duplex using Auxiliary port (higher bandwidth) | Communication may be full duplex using Auxiliary port (higher bandwidth) |
| Run-time control | Supports run time control debug using JTAG interface | Supports run time control debug using JTAG interface or Auxiliary port | Supports run time control debug using JTAG interface or Auxiliary port | Supports run time control debug using JTAG interface or Auxiliary port |
| Auxiliary Port Implementation | No Auxiliary Port | Allows sharing of Auxiliary port with slow (static) IO port pins | Allows Port sharing with high-speed I/O ports. | Allows Port sharing with high-speed I/O ports. |
| Data acquisition | Not supported | Not supported | Supports data acquisition | Supports data acquisition |
| Memory Substitution | Not supported | Not supported | Not supported | Supports memory substitution (fetching or reading data over NEXUS auxiliary port) Optional: Triggering memory substitution on a watchpoint |
Latest developments on the NEXUS Standard
Ashling Microsystems, as a member of the Nexus 5001 ForumT, brings to the initiative its expertise in both on-chip debug based debugging techniques and Software Quality Assurance tools such as Performance Analyzers and Code Coverage tools. Through close co-operation with Freescale (Motorola), Ashling has now introduced a scalable, universal range of tools that offer full support for the Freescale (Motorola) PowerPC MPC565 family of automotive embedded processors.
Successful implementation of both silicon and tools has allowed the NEXUST forum to 'work out the bugs' in the original specification and work is now well under way on the next revision (NEXUS 1.5) of the NEXUS specification. This revision aims to address any ambiguities or errors in the original; it also extends the connector options and adds improved support for high-speed tracing.
Visit www.nexus5001.org
to review the full Specification, or download 
Ashling's White Paper on The
NEXUST 5001 Standard: Gateway to the Embedded Systems of the Future.
Contact us: for advice on NEXUS implementations and tools and the latest information on NEXUS products and technologies.
IEEE-ISTO 5001 and Nexus 5001 Forum are trademarks of the IEEE-ISTO.
