lab-rv32i-freertos-static-task/doc/card-plan.md

K08 — DynamicTask, StaticTask, deletion and lifetime

Position

• Series: FreeRTOS C++
• Lesson: L07, card K08
• Duration: 30 minutes
• Real dynamic heap_4 plus caller TCB/stack in .bss
• Idle task itself and the verifier use static storage to isolate measurement

Outcome

After 30 minutes the student can calculate stack words and bytes, prove dynamic heap cost versus zero-delta static creation, classify TCB/stack addresses, and explain why self-deletion and actual dynamic memory reclamation are separated by idle-task cleanup.

Lesson plan

Time	Mode	Evidence
0–5	units/storage	predict 256 words, bytes and locations
5–10	dynamic create	measure heap delta and classify TCB/stack
10–15	static create	caller TCB/stack addresses; heap delta zero
15–20	run/complete	identical result 500500; wrappers completed/null
20–25	delete timing	heap still reduced immediately after self-delete
25–30	idle cleanup	block verifier; recover exact dynamic delta/baseline

Canonical timeline

baseline
 -> xTaskCreate(dynamic): heap - dynamic_cost
 -> xTaskCreateStatic(static): no heap change
 -> both run and complete
 -> both call vTaskDelete(nullptr)
 -> verifier runs before idle: dynamic storage still pending cleanup
 -> verifier blocks
 -> idle calls termination cleanup:
      dynamic TCB/stack -> vPortFree
      static TCB/stack  -> not freed (caller owned)
 -> verifier wakes: heap == baseline

Stable evidence

Evidence	Required relation
dynamic cost	baseline - after_dynamic > 0
static delta	after_static == after_dynamic
verifier delta	static verifier creation also leaves heap unchanged
dynamic addresses	TCB and stack base lie in ucHeap
static addresses	observed TCB/stack equal caller storage and lie outside heap
before idle	free equals post-create value, despite completed wrappers
after idle	free=baseline; recovered bytes=dynamic cost
units	256 StackType_t words = 1024 B on RV32I

Main traps

1. stack_depth counts words, not bytes.
2. vTaskDelete(nullptr) removes the current task from scheduling but dynamic memory reclamation is deferred to idle.
3. Static task deletion does not free caller storage; premature reuse is a lifetime bug.
4. A wrapper handle becoming null is not proof that idle cleanup already ran.
5. Forced deletion does not run arbitrary C++ destructors on the victim stack.

Acceptance

• host test proves both create APIs receive the same stable context and static native handle equals caller TCB;
• ABI proves static worker storage is .bss and no vtable/init runtime exists;
• static create and verifier create have exactly zero heap delta;
• dynamic cost is recovered only after the verifier lets idle run;
• both results are 500500, states completed, handles null and final PASS is 1.