Honor caller deadlines in Cortex-M and J-Link operations.

[jon]

Cortex-M acquisition, halt/resume/status, register access, and release now use the caller's context without adding a five-second deadline. J-Link configuration inspection also uses the caller's context, removing its one-second deadline and 101-attempt limit. It still retries only usb.ErrNotConfigured, with 10 ms between attempts.

For an already acquired, halted target, the call stays the same. Before, a thirty-second allowance was cut to five seconds:

readCtx, cancel := context.WithTimeout(ctx, 30*time.Second)
pc, err := core.ReadRegister(readCtx, cortexm.PC)
cancel()

After, the same call can use the full thirty seconds, unless ctx ends sooner:

readCtx, cancel := context.WithTimeout(ctx, 30*time.Second)
pc, err := core.ReadRegister(readCtx, cortexm.PC)
cancel()

The target still needs Release before its memory owner is closed. A failed transfer may leave cleanup pending; retain both owners and supply a usable context for restoration.

Likewise, before this change jlink.Open(ctx, device) stopped retrying an unconfigured device after one second or 101 attempts. Afterward, jlink.Open(ctx, device) retries until configuration appears or ctx ends. Ownership is unchanged: close the session on success, or the supplied device on error. A failed session close may need another attempt.

Why

The library was shortening caller deadlines even when the caller had deliberately allowed more time. Callers now choose their own limits. A context without a deadline or cancellation can wait indefinitely for a target transition or USB configuration.

Failed Cortex-M acquisition still attempts restoration with an independent five-second context. That cleanup must remain possible after cancellation; a non-nil target returned with an error retains any cleanup obligation for a later Release.

Documentation

The Cortex-M guide and API comments describe caller-owned deadlines, including release. The architecture guide and J-Link capability table describe configuration retries under the caller's context.

Hardware evidence

On macOS, two fresh CMSIS-DAP v2 sessions on the nRF51822 micro:bit at 1 MHz/AP0 read all 19 supported registers, wrote and restored R4/SP/MSP/PSP/PC, and resumed the counter program. The counter stopped while halted and advanced after resume and release. Both sessions restored initially disabled debug and running state before closing the Arm debug owner; both owners closed successfully. The bench used serial 9900360140124e4500279015000000360000000097969901 and the retained counter firmware:

OSTIOLE_CORTEXM_HIL_CONTROL=1 \
OSTIOLE_CORTEXM_HIL_REGISTERS=1 \
OSTIOLE_CORTEXM_HIL_PROGRAM=sha256:ee294cc06ab6e8228161b49506675b065c0148b26421cf1f83c8e45e35cd4e5d \
go test -tags integration ./target/cortexm \
  -run '^TestHILCortexM0Registers$' -count=1 -v

The J-Link EDU Mini V2 returned the same firmware metadata and selected interface across close and immediate reopen. Both sessions closed successfully:

OSTIOLE_JLINK_HIL=1 OSTIOLE_JLINK_HIL_SERIAL=000802011345 \
go test -tags integration ./jlink \
  -run '^TestHILJLinkMetadataSurvivesReopen$' -count=1 -v

These runs exercised ordinary operation after removing the limits; they did not provoke a slow target or prolonged unconfigured USB state. Deadline propagation, extended retries, and cancellation have behavioral-test coverage. No firmware was reloaded, and target state after the Arm owner closed was not measured.

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-27T00:54:06.265034Z	84c5fe3	Manual request
🔒 Security Review	✅ Completed 2026-09-27T00:54:43.968722Z	84c5fe3	PR opened

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[jon]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. 🚀

Reviewed commit: 84c5fe38bd

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