[

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
• KCD file format support

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/KCD
dbcparser dbc2 --dbc=file.dbc --format=C
# beauty or merge DBC/KCD
dbcparser dbc2 --dbc=file1.dbc --dbc=file2.kcd --format=DBC
# print DBC/KCD in human readable format
dbcparser dbc2 --dbc=file1.dbc --dbc=file2.kcd --format=human

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>intmain()
{
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>intmain()
{
constdbcppp_Nework*net=dbcppp_NetworkLoadDBCFromFile("your.dbc");
if (net)
{
can_frameframe;
while (1)
{
receive_can_frame_from_somewhere(&frame);
constdbcppp_Message*msg=nullptr;
auto n_msgs=dbcppp_NetworkMessages_Size(net);
for (uint64_ti=0; i<n_msgs; i++)
{
constdbcppp_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_ti=0; i<dbcppp_MessageSignals_Size(msg); i++)
{
constdbcppp_Signal*sig=dbcppp_MessageSignals_Get(msg, i);
uint64_traw=dbcppp_SignalDecode(sig, frame.data);
doublephys=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)