lab-rv32i-freertos-c-scheduler/doc/card-plan.md

Card plan — FC03

Goal

Make scheduler policy observable without teaching delays, queues, semaphores or C++ prematurely. A student must be able to distinguish priority selection from time slicing and show the difference in Hazard3/GDB.

Task

Task01 · Controlled scheduler experiment
├── A1 CONTEXT      timer -> tick ISR -> scheduler -> tasks
├── A2 STRUCTURE    contexts and bounded evidence records
├── A4 APPLICATION  four-task topology and priority contract
├── A5 FLOW         deterministic E01-E12 replay
├── A6 STATE        Ready/Running/Deleted and priority transition
├── A7 RUNTIME      CSRs, ISR stack, TCB/stack and committed traces
└── Exercise        bounded observation with time slicing disabled

A3 is not repeated because callback dispatch was established in FC02. A8 is not used because the scheduler policy is a kernel configuration rather than an application design pattern.

Runtime contract

1. high_probe is Ready at priority 0.
2. peer_a and peer_b are CPU-bound at priority 2.
3. verifier is Ready at priority 1 and cannot run while peers remain Ready.
4. The committed task-change trace must contain A-B-A.
5. Peer A records before_raise and calls vTaskPrioritySet(high, 3).
6. High records HIGH and self-deletes before the API call returns.
7. Peer A records after_raise, requests peer termination and both peers self-delete.
8. The verifier checks every invariant and exits with PASS.

The exact ordering claim applies to the three-marker projection only. Other legal scheduling activity may occur before peer A is selected again.

Exercise

Disable configUSE_TIME_SLICING while keeping both CPU-bound peers at the same priority. This is an expected-noncompletion experiment: observe for a bounded number of ticks that one peer may starve the other, capture the debugger state, then restore the configuration. The exercise does not redefine the card's PASS contract.

The series-level rationale and all FC03 acceptance gates are maintained in:

meta/workspace-info/plans/informatyka/freertos-c-fc03-a1-a8.md.