feat: add lab-rv32i-freertos-mutex card

2026-07-21 19:14:19 +02:00
commit 6419a78ff6
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+# K11 — Mutex, LockGuard and priority inheritance
+
+## Position
+
+- Series: FreeRTOS C++
+- Lesson: L10, card K11
+- Duration: 30 minutes
+- Actors: LOW=1, MEDIUM=2, HIGH=3, coordinator=4
+- Storage: static mutex control and static task stacks
+
+## Outcome
+
+The student distinguishes mutex ownership from semaphore signaling, repairs
+early returns with `LockGuard`, and explains every state/priority transition in
+a measured priority-inheritance schedule.
+
+## Lesson plan
+
+| Time | Mode | Evidence |
+| --- | --- | --- |
+| 0–5 | ownership | owner-only give; ordinary mutex non-recursive |
+| 5–10 | LockGuard | three returns each give exactly once |
+| 10–15 | setup | LOW takes; HIGH attempts; MEDIUM ready |
+| 15–20 | inheritance | HIGH blocked; LOW priority rises 1→3 |
+| 20–25 | release | MEDIUM has not run; HIGH acquires next |
+| 25–30 | restore | LOW returns to 1; protected counter is 11 |
+
+## Acceptance
+
+- mutex handle equals caller static control and heap delta is zero;
+- LOW owns at first checkpoint and HIGH owns after handoff;
+- HIGH is blocked while waiting;
+- LOW priority is exactly 1, then 3, then 1;
+- MEDIUM does not run before LOW release;
+- event order proves inherited LOW precedes MEDIUM;
+- guard restores on every host early-return path;
+- ordinary recursive attempt fails;
+- target exits with PASS and shared counter 11.
+
+## Main traps
+
+1. A binary semaphore is not an ownership mutex and has no inheritance.
+2. Ordinary mutex recursion deadlocks/fails; use a recursive type deliberately.
+3. Only the owner may unlock.
+4. Mutex APIs are not ISR APIs.
+5. Inheritance is temporary and bounded by the held mutex lifetime.