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.
- Class 1 supports run-time control (run, stop, memory upload/download when the processor is halted, breakpoints, read or set registers) using the JTAG interface. Communications are half duplex only and bandwidth is limited. Trace is not supported.
- Class 2 adds ownership trace and program trace and allows the auxiliary debugging port to be shared with "slow" I/O port pins. Ownership trace allows current task or current process trace for systems based on real-time kernels or operating-systems.
- Class 3 adds data write trace and memory read/write on-the-fly without halting execution. Data read/write tracing, sharing of the auxiliary port with high speed I/O ports such as the address/data bus, and support for data acquisition (visibility of related data parameters stored in internal resources, typically related calibration variables) may also be optionally part of Class 3 compliance.
- Class 4 adds memory substitution (fetching or reading data over the Nexus auxiliary port) and allows tracing to be triggered by a watchpoint. Triggering memory substitution on a watchpoint is an optional feature of Class 4 compliance.
Read more about this topic: Nexus (standard)
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