2011-01-08 20:11:12 -06:00
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+OpenOCD and CoreSight Tracing
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+
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Many recent ARM chips (Using e..g. Cortex-M3 and
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Cortex-M4 cores) support CoreSight debug/trace.
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This note sketches an approach currently planned for those cores
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with OpenOCD.
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This tracing data can help debug and tune ARM software, but not
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all cores support tracing. Some support more extensive tracing
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other cores with trace support +should be able to use the same
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approach and maybe some of the same analysis code.
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+the Cortex-M3 is assumed here to be the
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+core in use, for simplicity and to reflect current OpenOCD users.
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This note summarizes a software model to generate, collect, and
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analyze such trace data . That is not fully implemented as of early
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January 2011, +and thus is not *yet* usable.
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+
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+
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+Some microcontroller cores support a low pin-count Single-wire trace,
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with a mode where +trace data is emitted (usually to a UART. To use
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this mode, +SWD must be in use.
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+At this writing, OpenOCD SWD support is not yet complete either.
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(There are also multi-wire trace ports requiring more complex debug
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adapters than OpenOCD currently supports, and offering richer data.
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+
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+
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+* ENABLING involves activating SWD and (single wire) trace.
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+
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+current expectations are that OpenOCD itself will handle enabling;
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activating single wire trace involves a debug adapter interaction, and
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collecting that trace data requires particular (re)wiring.
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+
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+* CONFIGURATION involves setting up ITM and/or ETM modules to emit the
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+desired data from the Cortex core. (This might include dumping
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+event counters printf-style messages; code profiling; and more. Not all
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+cores offer the same trace capabilities.
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+
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+current expectations are that Tcl scripts will be used to configure these
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+modules for the desired tracing, by direct writes to registers. In some
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+cases (as with RTOS event tracking and similar messaging, this might
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+be augmented or replaced by user code running on the ARM core.
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+
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+COLLECTION involves reading that trace data, probably through UART, and
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+saving it in a useful format to analyse For now, deferred analysis modes
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are assumed, not than real-time or interactive ones.
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+
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+
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+current expectations are to to dump data in text using contrib/itmdump.c
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+or derived tools, and to post-process it into reports. Such reports might
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+include program messaging (such as application data streams via ITM, maybe
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+using printf type messaging; code coverage analysis or so forth. Recent
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+versions of CMSIS software reserve some ITM codespace for RTOS event
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tracing and include ITM messaging support.
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Clearly some of that data would be valuable for interactive debugging.
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+
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+Should someone get ambitious, GUI reports should be possible. GNU tools
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+for simpler reports like gprof may be simpler to support at first.
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+In any case, OpenOCD is not currently GUI-oriented. Accordingly, we now
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+expect any such graphics to come from postprocessing.
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2020-07-12 17:32:49 -05:00
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measurements for RTOS event timings should also be easy to collect.
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2011-01-08 20:11:12 -06:00
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+Examples include context and message switch times, as well as times
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for application interactions.
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+
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