6.9 KiB
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.