rust-embedded / rust-embedded/cortex-m

TPIU: `LAR` and `FFCR` not part of ARMv7-M standard

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O-Armv7-M
Dominant language
Rust
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Description

https://github.com/rust-embedded/cortex-m/blob/92552c73d3b56dc86007450633950d16ebe0e495/src/peripheral/tpiu.rs#L10-L34

c.f. https://developer.arm.com/documentation/ddi0403/d/Debug-Architecture/ARMv7-M-Debug/Trace-Port-Interface-Unit/TPIU-registers-summary

Both lar and ffcr introduced in c6ed9ef. lar is unused, but ffcr utilized in 720282f and refactored in fb604a7.

LAR is likely a part of the CoreSight standard, unsure about FFCR at the moment. Access to there registers should be gated if backing documentation can be found, otherwise removed.

I want to recall figuring FFCR out when I debugged openocd for an STM32 last year, but I need to verify that.

Contributor guide

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start in src/peripheral/tpiu.rs, especially the LAR and FFCR register definitions, and compare them with the linked ARMv7-M TPIU register summary. Review the referenced commits and verify whether FFCR is used by the existing API. Done means the registers are supported only where the documentation confirms them, or are removed when unsupported.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
embedded-iot
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
35/100

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