# FC03 — Tick, Priorities, Preemption and Time Slicing

FC03 is a freestanding C11 FreeRTOS card for RV32I/Hazard3. It turns the
scheduler rules from Chapter 4 of the official FreeRTOS Kernel Book into one
bounded, replayable experiment.

The program proves two independent facts:

```text
equal priorities:  peer A -> peer B -> peer A
priority change:   before_raise -> HIGH -> after_raise
```

The first trace is produced by two CPU-bound tasks at priority 2 with
preemption and time slicing enabled. The second trace is produced when peer A
raises a Ready task from priority 0 to priority 3. That task must run before
`vTaskPrioritySet()` returns to peer A.

## Book mapping

- Chapter 4.5 — task priorities;
- Chapter 4.6 — time measurement and the tick;
- Chapter 4.9 — changing task priority;
- Chapter 4.12 — time slicing.

The order of the FreeRTOS C series is curated for the laboratory. It is not a
claim that every optional chapter or API variant appears in the first fifteen
cards.

## Build and checks

```sh
make task1
make host-test
make check-abi
./scripts/run_sim.sh
./scripts/check_determinism.sh
```

`check-abi` rejects C++ runtime dependencies. The deterministic replay uses
application-owned records and public FreeRTOS APIs. Kernel internals may be
inspected in GDB, but they are never required by the application assertions.

## Evidence contract

- `E01`–`E05`: configuration, handles, priorities and scheduler start;
- `E06`: first bounded tick-hook observation;
- `E07`: committed A-B-A task-change trace;
- `E08`–`E10`: immediate-preemption marker projection;
- `E11`: peer self-deletion complete;
- `E12`: low-priority verifier publishes PASS.

The tick hook writes only a bounded diagnostic record and calls a dedicated
ISR-safe checkpoint sink. It does not print, allocate, block or use task-only
APIs.

## Generated material

`json/card_source.json` is the single card source. Rendering produces HTML and
TeX only; PDF generation and commits are separate, explicit operations.