feat: add lab-rv32i-freertos-sw-timer card

2026-07-21 19:14:20 +02:00
commit ae65adee32
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+# K14 — Software timer and the timer daemon task
+
+## Position
+
+- Series: FreeRTOS C++
+- Lesson: L13, card K14
+- Duration: 30 minutes
+- Policies: one-shot and periodic
+- Static timer/task storage; heap delta zero
+
+## Outcome
+
+The student separates command queue acceptance from callback execution,
+observes timer-daemon context, measures one-shot and periodic timelines, and
+states the lifetime contract for a typed callback context.
+
+## Lesson plan
+
+| Time | Mode | Evidence |
+| --- | --- | --- |
+| 0–5 | wrapper contract | non-copy, explicit start, typed context |
+| 5–10 | command queue | two starts accepted before scheduler, callbacks zero |
+| 10–15 | initial timeline | periodic ticks 2 and 4 |
+| 15–20 | reset/change | one-shot reset at 1 expires at 6; period 2→3 at 4 |
+| 20–25 | daemon proof | current handle/name and separate callback stack |
+| 25–30 | stop/lifetime | periodic tick 7, then inactive; no fourth callback |
+
+## Acceptance
+
+- OneShotTimer and PeriodicTimer encode reload policy in the type;
+- wrapper is neither copyable nor movable and start is explicit;
+- xTimerCreateStatic uses caller-owned control blocks in .bss;
+- both start commands return accepted while callback snapshot is still zero;
+- reset/change/stop acceptance is recorded separately from execution;
+- periodic callback ticks are exactly 2, 4 and 7;
+- reset at tick 1 moves one-shot expiry to tick 6 and it becomes inactive;
+- callback runs on timer daemon handle/name and a separate stack;
+- stopping the periodic timer prevents a fourth callback;
+- heap before/after timer creation is identical and target exits with PASS.
+
+## Main traps
+
+1. A callback runs in the timer service task, not in an ISR.
+2. pdPASS means the daemon queue accepted a command, not that it executed.
+3. Blocking or long work in one callback delays every software timer.
+4. Timer ID/context and StaticTimer_t storage must outlive pending work.
+5. Destroying a wrapper cannot synchronously prove queued deletion completed.