| name | tachograph |
| description | specialized knowledge for parsing/marshalling EU tachograph files. Use when needing to understand the .DDD/.V1B file format, TLV/TV protocols, ASN.1 mappings, or EU regulation compliance. |
EU Tachograph Domain Knowledge
This skill provides the domain expertise required to work with EU Tachograph files (Driver Card & Vehicle Unit).
Core Concepts
- Regulation First: All implementation must derive directly from EU regulations (Data Dictionary).
- Binary Fidelity: Support perfect round-trip parsing/marshalling (byte-for-byte exactness).
- Type Safety: Use specific types for specific generations/formats.
Workflows
1. Card File Structure (TLV)
- Architecture: See card_structure.md for TLV, DF/EF structure, and signature handling.
- Pattern: Use a "Two-Pass" parsing strategy (Raw TLV -> Semantic Structure).
2. Regulation & ASN.1
- Regulation: Consult regulation.md to locate specific chapters (Data Dictionary is critical).
- Definitions: Use ASN.1 definitions from the regulation as the source of truth for all data types.
3. Generations & Versions
- Details: See versions.md for a comprehensive overview of:
- Generation 1: Legacy (SHA-1, RSA-1024).
- Generation 2 V1: Smart Tachograph (SHA-256, ECC).
- Generation 2 V2: Smart Tachograph with GNSS/OSNMA support.
- Protocol Matrix: TLV (Card) vs TV (VU) tag ranges and structures.
- Detection: Use tag-based detection logic for both Card and VU files.
Best Practices for Implementation
Data Parsing
- ASN.1 Compliance: Every parser function should reference the ASN.1 definition from the spec.
- No Magic Numbers: Define constants for all binary offsets and lengths.
- Exact Lengths: Validate fixed-structure lengths exactly (
==), not loosely (>=).
- Nil Handling: The protocol has no concept of "null", only "default values" (e.g., spaces for strings, 0 for numbers). Parsing functions should handle missing or zero-length input safely.
Data Modeling
- Integers: Use signed integers (
int32/int64) for general numbers; the protocol rarely uses unsigned types in a way that maps cleanly to uint in all languages.
- Bitflags: Prefer boolean fields over integer bitmasks for clarity.
- Signatures: Model signed EFs by including a signature field (unless Regulation forbids).
