feat: add lab-rv32i-freertos-semaphore-notify card

2026-07-21 19:14:20 +02:00
commit 3ae96a0d06
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+# K12 — Semaphores and task notifications
+
+## Position
+
+- Series: FreeRTOS C++
+- Lesson: L11, card K12
+- Duration: 30 minutes
+- Waiter priority 3, signaler priority 2
+- Static semaphore controls; notification state in waiter TCB
+
+## Outcome
+
+The student selects a binary semaphore, counting semaphore or direct task
+notification from the communication cardinality and state semantics, then
+proves blocked/wake transitions and clear/value policy.
+
+## Lesson plan
+
+| Time | Mode | Evidence |
+| --- | --- | --- |
+| 0–5 | binary | empty 0, give 1, second give false, take 0 |
+| 5–10 | counting | max/initial 2, take to 1 then 0 |
+| 10–15 | blocked waiter | third take blocks; signaler observes eBlocked |
+| 15–20 | release | one give wakes exactly one waiter; token consumed |
+| 20–25 | notification count | give/take returns 1, state lives in TCB |
+| 25–30 | notification value | explicit overwrite/wait yields 0xA5A55A5A |
+
+## Acceptance
+
+- binary and counting bounds are enforced;
+- both handles equal caller static controls and heap delta is zero;
+- waiter is blocked at all three intended waits;
+- counting release is consumed immediately, leaving count 0;
+- notification give/take returns exactly 1;
+- explicit `overwrite` action transfers 0xA5A55A5A;
+- event order connects counting block/release and both notification phases;
+- target exits with PASS.
+
+## Main traps
+
+1. A semaphore signals availability; it does not carry a data record.
+2. Notification targets one specific task/slot, not arbitrary consumers.
+3. Clear-on-exit versus decrement changes binary/counting notification meaning.
+4. Wrong action or clear mask can silently lose bits/value.
+5. Identical wake behavior does not imply identical storage/cardinality.