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dbcppp

A C/C++ DBC file parser based on boost.spirit. This library is designed for decoding performance.

Features

• very fast decoding
• verbose parser output in error case
• DBC is editable through C/C++ interface exported from the library
• read/write DBC file
• decode functionality for frames of arbitrarily byte length
• cantools like decoding

Getting started

Build & Install

git clone --recurse-submodules https://github.com/xR3b0rn/dbcppp.git
cd dbcppp
mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE=Release ..
make -j
make RunTests
make install
ldconfig # on Unix-systems only

Usage example

Command line tool

dbc2

# generate C source from DBC
dbcparser dbc2 C file.dbc 
# beauty or merge DBC
dbcparser dbc2 DBC file1.dbc
# print DBC in human readable format
dbcparser dbc2 human file1.dbc

decode

cantools like decoding:

candump any | dbcppp decode --bus=vcan0,file1.dbc --bus=vcan1,file2.dbc

Library

• Examples
• C++

#include <fstream>
#include <dbcppp/Network.h>
int main()
{
    std::unique_ptr<dbcppp::INetwork> net;
    {
        std::ifstream idbc("your.dbc");
        net = dbcppp::INetwork::LoadDBCFromIs(idbc);
    }
    std::unordered_map<uint64_t, const dbcppp::IMessage*> messages;
    for (const dbcppp::IMessage& msg : net->Messages())
    {
        messages.insert(std::make_pair(msg.Id(), &msg));
    }
    can_frame frame;
    while (1)
    {
        receive_frame_data(&frame);
        auto iter = messages.find(frame.can_id);
        if (iter != messages.end())
        {
            const dbcppp::IMessage* msg = iter->second;
            std::cout << "Received Message: " << msg->Name() << "\n";
            for (const dbcppp::ISignal& sig : msg->Signals())
            {
                const dbcppp::ISignal* mux_sig = msg->MuxSignal();
                if (sig.MultiplexerIndicator() != dbcppp::ISignal::EMultiplexer::MuxValue ||
                    (mux_sig && mux_sig->Decode(frame.data) == sig.MultiplexerSwitchValue()))
                {
                    std::cout << "\t" << sig.Name() << "=" << sig.RawToPhys(sig.Decode(frame.data)) << sig.Unit() << "\n";
                }
            }
        }
    }
}

• C

#include <stdio.h>
#include <dbcppp/CApi.h>
int main()
{
    const dbcppp_Nework* net = dbcppp_NetworkLoadDBCFromFile("your.dbc");
    if (net)
    {
        can_frame frame;
        while (1)
        {
            receive_can_frame_from_somewhere(&frame);
            const dbcppp_Message* msg = nullptr;
            auto n_msgs = dbcppp_NetworkMessages_Size(net);
            for (uint64_t i = 0; i < n_msgs; i++)
            {
                const dbcppp_Message* msg = dbcppp_NetworkMessages_Get(i);
                if (dbcppp_MessageId(tmp) == frame.can_id)
                {
                    printf("Received message: %s\n", dbcppp_MessageGetName(msg));
                    dbcppp_MessageForEachSignal(msg, print_signal_data, &frame);
                    for (uint64_t i = 0; i < dbcppp_MessageSignals_Size(msg); i++)
                    {
                        const dbcppp_Signal* sig = dbcppp_MessageSignals_Get(msg, i);
                        uint64_t raw = dbcppp_SignalDecode(sig, frame.data);
                        double phys = dbcppp_SignalRawToPhys(sig, raw);
                        printf("\t%s=%f\n", dbcppp_SignalName(sig), phys);
                    }
                }
            }
        }
    }
    dbcppp_NetworkFree(net);
}

DBC data types

Supported

• version
• new_symbols
• bit_timing
• nodes
• value_tables
• messages
• message_transmitters
• environment_variables
• environment_variables_data
• signal_types
• comments
• attribute_definitions
• attribute_defaults
• attribute_values
• value_descriptions
• signal_extended_value_type_list
• signal_groups
• signal_multiplexer_value

Not supported yet

• sigtype_attr_list
• signal_type_refs

Decode-function

The signals decode function is using prestored masks and fixed offsets to speed up calculation, therefore the decoding-function should be almost as fast as a code generated decode function would be. The assembly of the decode-function on its critical path (signed and byte swap must happen) looks like this (VS19 10.0.18362.0 compiler):

template <Alignment aAlignment, Signal::ByteOrder aByteOrder, Signal::ValueType aValueType, Signal::ExtendedValueType aExtendedValueType>
double template_decode(const Signal* sig, const void* nbytes) noexcept
00007FF8025BCA73  mov         rax,rcx  
00007FF8025BCA76  mov         rcx,qword ptr [rcx+140h]  
00007FF8025BCA7D  xorps       xmm0,xmm0  
00007FF8025BCA80  bswap       r8  
00007FF8025BCA83  shr         r8,cl  
00007FF8025BCA86  and         r8,qword ptr [rax+130h]  
00007FF8025BCA8D  mov         rcx,qword ptr [rax+138h]  
00007FF8025BCA94  mov         rax,rcx  
00007FF8025BCA97  or          rcx,r8  
00007FF8025BCA9A  and         rax,r8  
00007FF8025BCA9D  cmove       rcx,r8  
00007FF8025BCAA1  cvtsi2sd    xmm0,rcx  
00007FF8025BCAA6  ret   

On the best path (no byteswap must take place and ExtendedValueType == Double) the decode function only has 5 instructions:

template <Alignment aAlignment, Signal::ByteOrder aByteOrder, Signal::ValueType aValueType, Signal::ExtendedValueType aExtendedValueType>
double template_decode(const Signal* sig, const void* nbytes) noexcept
00007FF8025BCAF0  mov         rax,qword ptr [rdx]  
00007FF8025BCAF3  mov         qword ptr [rsp+8],rcx  
00007FF8025BCAF8  mov         qword ptr [sig],rax  
00007FF8025BCAFD  movsd       xmm0,mmword ptr [data]  
00007FF8025BCB03  ret  

Known issues

• tests for decoding function for float/double is failing on some machines (currently only confirmed for System/s390x)

Similar projects

• Vector_DBC Does basically the same, the biggest difference is that it uses bison instead of boost::spirit for grammar parsing
• CAN BUS tools in Python 3 (cantools)