Diagnostic Log and Trace

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Diagnostic Log and Trace

Welcome to COVESA Diagnostic Log and Trace (DLT). If you are familiar with DLT and want to know what's new, check the Release Notes.

New to DLT? Great! Welcome aboard. We prepared a brief overview for you as well as some information on how to get started immediately. After you made yourself familiar with the basic mechanics of DLT, you can learn more about advanced concepts and features.

Overview

COVESA DLT provides a log and trace interface, based on the standardised protocol specified in the AUTOSAR Classic Platform R19-11 DLT. It is used by other COVESA components but can serve as logging framework for other applications without relation to COVESA.

The most important terms and parts are depicted in the following figure. Please refer to Glossary for a full overview over DLT-specific terms.

A DLT User essentially is an application that serves its respective (not DLT-related) purpose and produces DLT log messages. It utilizes the DLT library to craft and transmit these messages.
The DLT Library provides a convenient API to DLT Users (i.e. applications) to create DLT log messages and hand them over to the DLT Daemon. If the latter is not avilable, the library will cache the messages in a ring buffer so they don't get lost immediately.
The DLT Daemon is the DLT communication interface of an ECU. It collects and buffers log messages from one or more DLT users running on the ECU and provides them to DLT clients upon their request. The daemon also accepts control messages from the clients to adjust the daemon's or the aplications' behaviour.
A DLT Client receives and consumes the log messages from DLT Users by fetching them from DLT Daemons. It may also issue control messages to control the behaviour of a DLT Daemon or its connected DLT Users. A DLT client can even transmit user-defined data to a DLT User through so-calles injection messages.

This is only the simplest of all use cases that you will further pursue in the Get Started section. Once you want to learn more, you will find that the repository contains advanced features utilizing several adaptors and console utilities as well as test applications.

Get Started

In this section, you can learn how to build and install DLT. Then you can choose to run a DLT demo setup or to start by developing your own DLT-featured application.

Build and install

The following packages need to be installed in order to be able to build and install DLT daemon:

cmake
zlib
dbus
json-c (only required for dlt-receives extended filtering)

On Ubuntu those dependencies can be installed with the following command:

sudo apt-get install cmake zlib1g-dev libdbus-glib-1-dev build-essential
optional: sudo apt-get install libjson-c-dev # in case you want to use dlt-receives extended filtering

Then proceed to download DLT if you haven't already. We recommend cloning the repository, but downloading and extracting a zip-archive is fine as well.

cd /path/to/workspace
git clone https://github.com/COVESA/dlt-daemon.git

To build and install the DLT daemon, follow these steps:

cd /path/to/workspace/dlt-daemon
mkdir build
cd build
cmake ..
make
optional: sudo make install
optional: sudo ldconfig # in case you executed make install

For DLT on Cygwin please refer to Build and Install DLT on Cygwin

CMake accepts a plethora of build options to configure the build to suit your needs.

Run a DLT demo

In case you haven't had a look at the brief overview, now would be the perfect occasion to learn about the most important terms and to get an idea where data is buffered. Then go on with our guide on how to set up a DLT demo setup.

Develop your own DLT-featured application

Now that you have seen DLT in action, you probably want to develop your own applications using DLT. You will find everything you need in our "DLT for Application Developers" guide.

A hint: If you want to read the API documentation, you have to build it locally at the moment. The API documentation is generated with doxygen. To build it, run cmake with the -DWITH_DOC=ON option, e.g.:

mkdir build
cd build
cmake -DWITH_DOC=ON ..
make doc

Build DLT debian package

To build the DLT debian package for your own purpose, follow these steps:

dpkg-buildpackage -us -uc

Learn more

Once you got your feet wet with developing your first application, you might want to learn more. Find out about DLT's advanced topics, learn how to configure, control and interface DLT or study its internals by checking out the design specifications.

Advanced Topics

The COVESA DLT implementation is capable of by far more than to "just" send log message. You will get an overview of advanced features in this section. Follow the links to learn more about the respective concept.

Document	Description
Build Options	The CMake build system provides a large amount of build options. They let you turn on or off certain features and provide alternative implementation details.
LogStorage	The DLT Daemon as well as the DLT libary provide buffers for caching log data during absence of a consumer. However, some use cases require to write large amounts of log message e.g. to mass storages for long term storage or because no other means of exfiltrating the log data is available.
MultiNode	A DLT Daemon can run as a gateway to connect multiple passive nodes. Each passive node has its owns DLT Applications and runs its own daemon. The gateway node connects to all of them, collects the logs and routes them to the DLT Client.
Extended Network Trace	Normal DLT messages are limited in size. To overcome this limitation the feature network trace message allows the user to send or truncate messages which would not fit into a normal DLT message.
DLT Filetransfer	Although not originally designed for this, files can be transmitted over DLT. A corresponding DLT Client (e.g. DLT Viewer) can receive and decode them accordingly.
DLT KPI	Valueable status information about the monitored system can be read via DLT as well. The information under `/proc` of the target system is at your hands easily.
DLT Core Dump Handler	This tool collects and extracts debug information then utilize DLT Filetransfer to transfer the information to client.

Configure, Control and Interface

There is still lots to discover about DLT. If you turn on the generation of manpages with the cmake option -DWITH_MAN=ON you can learn how to configure DLT to exactly suit your needs, how to control the behvaiour of running instances and how to interface DLT with existing system through provided adaptors.

The man pages are generated with pandoc, which also needs asciidoc as dependency.

Build manpages (initally or because something changed) with e.g.

mkdir build
cd build
cmake -DWITH_MAN=ON ..
make generate_man

Document	Description
Configuration
dlt-daemon(1)	How to start DLT-Daemon
dlt.conf(5)	Configure the DLT framework to reflect your use case
Control running instances of DLT
dlt-receive(1)	Receive DLT messages from daemon and print or store the log messages.
dlt-control(1)	Send control messages to daemon.
dlt-logstorage-ctrl(1)	Send a trigger to daemon to connect/disconnect certain logstorage device, or send a demand to sync data the internal buffer into logstorage file.
dlt-passive-node-ctrl(1)	Send a trigger to daemon to connect/disconnect passive daemon.
Interfacing DLT
dlt-system(1)	DLT-System provides a way to directly access system logs via DLT
dlt-system.conf(5)	Configure DLT-System
dlt-adaptor-stdin(1)	Adaptor for forwarding input from stdin to daemon.
dlt-adaptor-udp(1)	Adaptor for forwarding received UDP messages to daemon.
dlt-convert(1)	Convert DLT files into human readable format.
dlt-sortbytimestamp(1)	Read log messages from DLT file, sort by timestamp, and store them again.
dlt-qnx-system(1)	Access system logs in QNX with DLT

Contribution

Start working, best practice is to commit smaller, compilable pieces during the work that makes it easier to handle later on.

If you want to commit your changes, create a Pull Request in Github. Please make sure to follow the Rules for commit messages

Coding Rules

This project is now using clang-format as replacement of uncrustify.

For convenience, any code changes will be harmonized before commit by hooks/pre-commit.

Install clang-format

Install pre-commit script by:

cp scripts/pre-commit.sample .git/hooks/pre-commit

Configuration: .clang-format

For reference to clang-format, you can check with: Configurator

Known issues

List of open issues can be found on Github

DLT library: Usage of dlt_user_log_write_float64() and DLT_FLOAT64() leads to "Illegal instruction (core dumped)" on ARM target.
DLT library: Nested calls to DLT_LOG_ ... are not supported, and will lead to a deadlock.
For Non linux platforms [eg: QNX] IPC supported is UNIX_SOCKET. For Linux Platforms both IPC FIFO and UNIX_SOCKET are supported

Software/Hardware

Developed and tested with Ubuntu Linux 16 64-bit / Intel PC

License

Full information on the license for this software is available in the "LICENSE" file. Full information on the license for the cityhash code is available in "COPYING" file in src/core_dump_handler/cityhash_c.

Contact

Tin Le Tin.Le@vn.bosch.com; Minh Luu Quang Minh.LuuQuang@vn.bosch.com