lab-rv32i-freertos-semaphore-notify/doc/card-plan.md

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.