feat: add lab-rv32i-freertos-event-group card

2026-07-21 19:13:55 +02:00
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+# K13 — EventGroup and coordinated state
+
+## Position
+
+- Series: FreeRTOS C++
+- Lesson: L12, card K13
+- Duration: 30 minutes
+- Typed bits: UART=0x1, GPIO=0x2, APP=0x4
+- Static control block; no heap delta
+
+## Outcome
+
+The student designs a typed readiness mask, distinguishes any/all and
+keep/clear-on-exit, explains timeout snapshots, and rejects the interpretation
+of an event bit as a counter or payload.
+
+## Lesson plan
+
+| Time | Mode | Evidence |
+| --- | --- | --- |
+| 0–5 | typed masks | enum bits combine to all=0x7 |
+| 5–10 | publishers | coordinator Blocked; workers set 1,2,4 |
+| 10–15 | wait all | snapshot/current=0x7, satisfied |
+| 15–20 | clear one | clear GPIO returns 0x7, current=0x5 |
+| 20–25 | timeout | all unsatisfied for 3 ticks, snapshot=0x5 |
+| 25–30 | any + clear | snapshot=0x5, final=0; discuss races/counters |
+
+## Acceptance
+
+- type is an enum and masks remain typed at the wrapper boundary;
+- event-group handle equals caller static control and heap delta is zero;
+- coordinator is eBlocked before the first worker publishes;
+- repeated UART set is idempotent at mask 1;
+- all/keep gives 7 and explicit GPIO clear gives 5;
+- second all wait times out after at least 3 ticks with snapshot 5;
+- any/clear-on-exit succeeds with snapshot 5 and final mask 0;
+- target exits with PASS.
+
+## Main traps
+
+1. A bit is state, not an event count.
+2. A bit mask is not a payload record.
+3. Clear-on-exit affects all selected bits and can race with other waiters.
+4. Timeout return is a snapshot; test satisfaction explicitly.
+5. EventGroup FromISR set is deferred through the timer service task.