DBC Parser Documentation Overview This module implements a minimal DBC parser intended for use in the FrameTap project. Its purpose is to read a DBC file and convert it into an internal representation that can later be used for: displaying CAN frames and signals building a hierarchical structure for UI integrating with Qt Model/View selecting signals for plotting preparing for runtime CAN/J1939 decoding The implementation intentionally follows the KISS principle: simple readable easy to modify independent from Qt This is not a full DBC parser, but a practical foundation that can be extended gradually. Architecture The module uses a simple processing pipeline. DBC file ↓ DbcParser ↓ DbcDatabase ↓ DbcTreeBuilder ↓ TreeNode hierarchy ↓ Future Qt Model/View integration Each component has a clear responsibility. Component Responsibility DbcParser Reads and parses the DBC file DbcDatabase Stores parsed frames and signals DbcTreeBuilder Converts the database into a tree TreeNode Represents hierarchical nodes This separation allows the parser to remain independent from UI or visualization logic. File Structure The module consists of several logical parts. Data structures Files: signal_info.h frame_info.h dbc_database.h These files define the internal representation of parsed data. Tree representation Files: tree_node.h tree_node.cpp Defines a simple hierarchical structure that can later be used by UI components. Parser Files: dbc_parser.h dbc_parser.cpp Responsible for reading the DBC file and extracting frame and signal information. Tree builder Files: dbc_tree_builder.h dbc_tree_builder.cpp Converts the parsed database into a tree representation. Data Structures SignalInfo Represents a single signal defined in a DBC file. Fields: name startBit length isLittleEndian isSigned factor offset minimum maximum unit receivers comment Notes: receivers may contain multiple ECUs comment is optional factor and offset define physical conversion Physical value is calculated as: physical = raw * factor + offset FrameInfo Represents a CAN frame. Fields: name canId dlc transmitter comment signals pgn hasPgn Notes: signals is a vector of SignalInfo transmitter is the ECU that sends the frame pgn is derived if the frame appears to follow J1939 rules DbcDatabase Top level container for parsed data. DbcDatabase └── vector This structure represents the entire DBC file content. Tree Representation The module converts the parsed data into a tree. Node types: Root Frame Signal Example structure: dbc ├── EngineData │ ├── EngineSpeed │ ├── OilTemp │ └── CoolantTemp └── VehicleData ├── VehicleSpeed └── Odometer Each node stores either: FrameInfo SignalInfo This tree structure is designed to integrate easily with Qt Model/View. Parser The parser is implemented in: dbc_parser.h dbc_parser.cpp It performs line-based parsing of the DBC file. Supported elements: BO_ SG_ CM_ Supported DBC Syntax Frame Definition Example: BO_ 256 EngineData: 8 EEC1 Parsed values: Field Meaning 256 CAN identifier EngineData frame name 8 DLC EEC1 transmitter ECU Signal Definition Example: SG_ EngineSpeed : 0|16@1+ (0.125,0) [0|8000] "rpm" ECU1,ECU2 Parsed values: Field Meaning EngineSpeed signal name 0 start bit 16 signal length @1 little endian + unsigned factor 0.125 offset 0 minimum 0 maximum 8000 unit rpm receivers ECU1, ECU2 Comments Frame comment: CM_ BO_ 256 "Engine data frame"; Signal comment: CM_ SG_ 256 EngineSpeed "Actual engine speed"; These values are stored in: FrameInfo::comment SignalInfo::comment PGN Extraction PGN is derived using simplified J1939 logic. Typical J1939 identifier layout: Priority Reserved Data Page PDU Format PDU Specific Source Address The parser extracts PGN from the 29-bit CAN ID. This is a simplified approximation and should not be considered full J1939 validation. Example Usage Typical usage: DbcParser parser; DbcDatabase database = parser.ParseFile("example.dbc"); DbcTreeBuilder builder; std::unique_ptr root = builder.Build(database); After this step, the tree can be used by a UI or visualization system. Example Tree Example output structure: dbc ├── EngineData │ ├── EngineSpeed │ ├── OilTemp │ └── CoolantTemp └── VehicleData ├── VehicleSpeed └── Odometer Limitations The current implementation intentionally does not support many advanced DBC features. Not supported yet: multiplexed signals BA_ attributes BA_DEF_ definitions VAL_ value tables signal groups advanced comments complex syntax variations These can be added later if required. Design Principles KISS The parser is intentionally simple. It avoids complex grammar systems and tokenizers in order to keep the code easy to understand and maintain. Separation of Concerns Parsing, storage, and tree building are separate components. This makes it easier to: test the parser change UI representation export data reuse the module elsewhere Qt Independence The parser itself does not depend on Qt. Qt integration should be implemented through a separate adapter layer. Future Development Recommended evolution path. Stage 1 (current) BO_ SG_ CM_ transmitter receivers basic PGN extraction tree representation Stage 2 Add: extended CAN ID detection better PGN extraction TreeNode parent pointer Qt Model adapter Stage 3 Add support for: VAL_ value tables BA_ attributes BA_DEF_ definitions extended comments Stage 4 Advanced functionality: multiplexing runtime signal decoding integration with CAN stream drag-and-drop plotting Intended Usage in FrameTap This module will allow FrameTap to: load DBC files display frames and signals select signals search signals display metadata prepare runtime decoding Example workflow: Load DBC ↓ Browse signals ↓ Select signal ↓ Decode CAN frames ↓ Plot physical values Why Abstract Factory Is Not Used An abstract factory is intentionally not used at this stage. The current structure already separates responsibilities clearly: parser → database → tree builder → tree Introducing factories now would increase complexity without significant benefit. Factories can be added later if multiple internal representations are required. Build Integration The module is independent of any specific build system. It can be integrated using: CMake qmake Makefile Simply add the source files to the project. Summary This module provides a minimal but extensible DBC parser designed for FrameTap. Key properties: simple modular Qt-independent extendable It converts a DBC file into an internal structure: frame → signals with additional metadata such as: transmitter receivers comments basic PGN information This forms the foundation for future CAN signal visualization and decoding.