[jon]

cortexm.AcquireGroup acquires an explicit set of Cortex-M0/M33 targets over borrowed memory clients. Selected halt, resume, and status calls return per-core outcomes, including members not reached after a failure; register and step access stays inside the owned targets.

group, err := cortexm.AcquireGroup(ctx, []cortexm.Member{
    {ID: 1, Memory: memory0},
    {ID: 2, Memory: memory1},
})
if err == nil {
    _, err = group.Halt(ctx, 1, 2)
    if err == nil {
        _, err = group.Status(ctx, 1, 2)
    }
    if err == nil {
        _, err = group.ReadRegister(ctx, 1, cortexm.PC)
    }
    if err == nil {
        err = group.WriteRegister(ctx, 1, cortexm.R4, r4Value)
    }
    if err == nil {
        err = group.Step(ctx, 1)
    }
    if err == nil {
        _, err = group.Resume(ctx, 1)
    }
}
cleanup, cancel := context.WithTimeout(context.Background(), 5*time.Second)
_, releaseErr := group.Release(cleanup)
cancel()
err = errors.Join(err, releaseErr)
if releaseErr == nil {
    err = errors.Join(err, owner.Close())
}

The memory clients above are borrowed from one Arm owner; r4Value is an intentional register change which persists after release. If release fails, retain the group and Arm owner for another cleanup attempt. Group.Results copies the latest member outcomes without traffic.

Why

Separate targets already control the RP2350 cores, but their caller must track partial progress and cleanup independently. The group owns that lifecycle, preserves inherited halts, releases only halt requests it still owns, and attempts independent cleanup after a member fails. The caller still serializes calls over the shared connection. Sequential stopping does not promise simultaneous halt, and the group does not own CTI routing.

Documentation

Update the Cortex-M guide, architecture, composition, and capability table with group ownership, selected control, member access, and cleanup limits.

Hardware evidence

On the prepared RP2350 Secure dual-counter bench, J-Link EDU Mini V2 000802011345 at 1 MHz with APs 0x2000/0x4000, run:

OSTIOLE_RP2350_HIL_GROUP=1 \
OSTIOLE_RP2350_HIL_PROGRAM=bf878b47815bc5eaf6afb5279efaa6ff163832bd178c5b7b1604f80e6ad6cde9 \
go test -tags integration ./target/cortexm -run '^TestHILRP2350Group$' -count=1 -v

Two fresh sessions read all 19 registers on each core, verified one PC/R0/RAM step per core while its peer advanced, stopped both cores sequentially, verified another core-0 step while its peer stayed stopped, and resumed only core 0. In each session, group release restored progress on both cores and their initial disabled-debug/running state before the shared owner closed; DSCSR and inactive CTI configuration were unchanged. Group release and owner close succeeded in both sessions. Post-close state was not independently measured. Register writes and injected failures were not exercised physically, and the prepared RAM programs and instruction effects remain.

[jon]

@codex review

[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 2026-10-04T19:47:02.616298Z	4331bf6	Manual request
🔒 Security Review	✅ Completed 2026-10-04T19:39:50.379811Z	4331bf6	PR opened

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[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 4331bf6c64

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[jon]

@codex review

Please review the individual commits as well as the final diff. The previous commit-size finding counted the complete PR as one commit; the published series already separates acquisition/release (89ecdf0, 168 added non-test Go lines), selected control (0098318, 156), and member access (4331bf6, 43), each with tests and documentation. The head remains 4331bf6.

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. You're on a roll.

Reviewed commit: 4331bf6c64

ℹ️ About Codex in GitHub

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• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".