13.1. Additional Material
Trace Bandwidth Considerations
SRC field (if enabled) may change the otherwise optimal layout of Fields in Messages.
Validation Considerations
ResourceFull message with I-CNT full is rare and may not be experienced in normal code. Simplest way to generate is to have an infinite loop and (rare) interrupt handler. This loop should increment a register or memory location - this value should correspond to total accumulated I-CNT.
Potential Future Enhancements
Table below is proposing some future enhancements for N-Trace messages. These were discussed during the development of the N-Trace specification.
| Enhancement | Conformance | Notes |
|---|---|---|
Instrumentation Data Trace |
Nexus Compatible |
Very likely (Nexus defines appropriate messages). It will require software to be instrumented by code sending data using trace infrastructure (Arm CoreSight ITM enabled many use-cases). |
Selective Data Trace |
Nexus Compatible |
Very likely (Nexus defines appropriate messages). It will allow sending some data in response to triggers (from debug module or external). |
Full Data Trace |
Nexus Compatible |
Likely (E-Trace supports it), but necessary bandwidth may be a problem. |
Smaller field sizes |
Nexus Extension |
Unlikely (too much of a change). Some of the fields may be made shorter (as not all cases are needed), but it may not be justified. |
System Bus Trace |
Nexus Compatible |
Likely (Nexus defines appropriate messages and there is a need for more than trace of harts). |
Additional TCODE |
Nexus Extension |
Possible, but more real-life examples are needed to justify it. |
Single MSEO bit |
Nexus Compatible |
Unlikely to be considered. It may provide (12.5% instead of 25% MSEO overhead), but it is more complex to handle by both encoder and decoders. |
More MDO bits |
Nexus Compatible |
Very unlikely to be considered. To keep byte alignment, 14 or 22 or 30-bit MDO may be considered. Even 14-bit will cause a lot of 'wasted' bits. |
| Each of the above enhancements should be first prototyped and validated using reference C encoder/decoder. |