---
nc-id: NC-001
project: demo-epb
date-discovered: 2026-05-11
severity: Critical
status: Closed
---

# Non-Conformity NC-001: Step counter overflow not documented

| Field                | Value                              |
|---------------------|-----------------------------------|
| NC ID               | NC-001                            |
| Project             | demo-epb                          |
| Date discovered     | 2026-05-11                        |
| Discovered by       | Review REV-001                    |
| Affected artefact    | `src/apply_controller.c`          |
| Requirement         | SWE-002 (watchdog)                |
| Severity            | Critical                          |
| Status              | Closed                            |

---

## 1. Description

`step_count` in the apply controller is declared as `uint32_t` and is monotonically incremented in `apply_ctrl_step_50ms`. At 50 ms/tick the counter overflows after 2^32 * 50 ms ≈ 6.8 years. The watchdog in SWA-002 only compares the delta between two reads (wrap-around safe), but the behaviour is not documented in the header and may lead to errors in subsequent maintenance.

## 2. Risk assessment

| Aspect            | Assessment                                                       |
|-------------------|-------------------------------------------------------------------|
| Effect            | In theory false-negative watchdog on wrap-around comparison       |
| Likelihood        | Very low (6.8 years lifetime)                                     |
| Safety contribution | Indirect — watchdog is part of the SG-01 implementation         |

## 3. Immediate action

Header comment in `apply_controller.h` extended: explicit description of wrap-around behaviour. The watchdog implementation (in SWA-001) must use `uint32_t` subtraction for delta comparison (wrap-safe).

## 4. Corrective action (root cause)

Add the checklist item "document integer overflow behaviour" to the code-review checklist. Verify in subsequent reviews.

## 5. Verification

- Comment in `apply_controller.h` v1.1 (commit `<hash>`)
- Watchdog in SWA-001 uses `uint32_t` subtraction (see SWA-001 §4)
- Review checklist updated

## 6. Closure

Closed on 2026-05-11 by S. Lohmaier after verification.