# K10 — Queue<T> and StaticQueue<T, N>

## Position

- Series: FreeRTOS C++
- Lesson: L09, card K10
- Duration: 30 minutes
- Platform: Hazard3 / RV32I, FreeRTOS V11.3.0
- Message: 12-byte trivial `Sample`, capacity 2

## Outcome

The student explains byte-copy semantics, designs a trivial message, proves a
copy survives source mutation, compares dynamic and caller-owned static queue
storage, and handles full/empty states with explicit bounded timeouts.

## Lesson plan

| Time | Mode | Evidence |
| --- | --- | --- |
| 0–5 | type contract | `Sample` passes; owning `VectorV1` fails |
| 5–10 | create | dynamic cost 128 B; static delta 0 B |
| 10–15 | copy | send, mutate source, receive unchanged copy |
| 15–20 | storage | inspect first 12 static storage bytes |
| 20–25 | full/timeout | capacity 2; third send fails after 2 ticks |
| 25–30 | FIFO/drain | values 0x2222 then 0x3333; empty receive fails |

## Acceptance

- `sizeof(Sample)==12` reaches both create APIs;
- dynamic cost is positive and recovered by RAII destruction;
- static create has zero heap delta and its buffers are in `.bss`;
- received value remains 0x1111 after source becomes 0xDEAD;
- storage snapshot equals the first sent `Sample` byte-for-byte;
- full count is 2, third send returns false after at least 2 ticks;
- FIFO and non-blocking empty receive are correct;
- non-trivial owning message fails for the pinned static-assert reason;
- target exits with PASS.

## Main traps

1. Queue storage is a byte copy, not a C++ object owner.
2. `sizeof(pointer)` plus an object address is a different and invalid contract.
3. A trivially-copyable pointer still needs an external lifetime policy.
4. `portMAX_DELAY` must not be hidden as a convenient default.
5. Static queue control and byte storage must both outlive the queue.