Automotive Logging

1 skill files covering logging domain for automotive software engineering.

Required Tools

• DLT Viewer (optional, for visualization)
• Python 3.8+
• dlt-daemon (optional, for network logging)

Instructions

dlt-logging

DLT (Diagnostic Log and Trace) Guide — AUTOSAR/COVESA

Overview

DLT is the standardized logging framework for automotive systems, defined by AUTOSAR and maintained by COVESA. It provides structured, high-performance logging with application/context-based filtering, binary message format for efficiency, and support for multi-ECU log aggregation.

Architecture

Application 1        Application 2        Application N
┌─────────────┐     ┌─────────────┐     ┌─────────────┐
│ DLT User    │     │ DLT User    │     │ DLT User    │
│ Library     │     │ Library     │     │ Library     │
└──────┬──────┘     └──────┬──────┘     └──────┬──────┘
       │                   │                   │
       └───────────────────┼───────────────────┘
                           │ UNIX Socket / Shared Memory
                  ┌────────┴────────┐
                  │  DLT Daemon     │
                  │  (dlt-daemon)   │
                  ├─────────────────┤
                  │ File Output     │ → /var/log/dlt/*.dlt
                  │ Network Output  │ → TCP port 3490
                  │ Serial Output   │ → /dev/ttyS0
                  └─────────────────┘
                           │ TCP/IP
                  ┌────────┴────────┐
                  │  DLT Viewer     │  (Desktop analysis tool)
                  └─────────────────┘

Identification Model

DLT uses a hierarchical ID system for filtering:

• ECU ID (4 chars): Identifies the hardware unit (e.g., "ECU1", "GW01")
• Application ID (4 chars): Identifies the software application (e.g., "ADAS", "DIAG")
• Context ID (4 chars): Identifies the subsystem within an app (e.g., "CTRL", "SENS")

This enables precise filtering: show only ADAS.CTRL errors from ECU1.

Log Levels

| Level | Value | Usage | |-------|-------|-------| | FATAL | 0x01 | System failure, requires immediate action | | ERROR | 0x02 | Error condition, operation failed | | WARN | 0x03 | Potential problem, degraded operation | | INFO | 0x04 | Normal operational events | | DEBUG | 0x05 | Detailed debug information | | VERBOSE | 0x06 | Maximum detail (development only) |

Message Format

DLT messages use a compact binary format for efficiency:

┌──────────────┬──────────────┬──────────────┬──────────────┐
│ Storage Hdr  │ Standard Hdr │ Extended Hdr │ Payload      │
│ (16 bytes)   │ (4 bytes)    │ (10 bytes)   │ (variable)   │
└──────────────┴──────────────┴──────────────┴──────────────┘

Storage Header: timestamp (seconds + microseconds), ECU ID
Standard Header: version, message counter, length, ECU ID
Extended Header: message info, app ID, context ID
Payload: type-safe arguments (string, int, float, raw data)

Verbose vs Non-Verbose Mode

• Verbose mode: Payload includes type info per argument (self-describing).

Larger messages but viewable without external database.

• Non-verbose mode: Payload is raw data, requires FIBEX database to decode.

Smaller messages, used in production for bandwidth savings.

DLT Daemon Configuration

Key configuration file: /etc/dlt.conf

ini
# DLT daemon configuration
Verbose = 1                    # Enable verbose mode
DaemonFIFOSize = 65536        # FIFO buffer size
LoggingLevel = INFO            # Daemon's own log level
OfflineTraceDirectory = /var/log/dlt  # File output directory
OfflineTraceFileSize = 10000000       # Max file size (10MB)
OfflineTraceMaxSize = 100000000       # Max total size (100MB)
ECUId = ECU1                   # This ECU's identifier

Multi-ECU Logging

For distributed automotive systems:

• Each ECU runs its own dlt-daemon with unique ECU ID
• Central logger connects to all ECUs via TCP port 3490
• DLT Viewer aggregates and time-correlates logs from all ECUs
• Use NTP or PTP for time synchronization across ECUs

Integration with Python

The DLTAdapter in this project wraps the DLT protocol for Python applications. Key patterns:

• Use context managers (with DLTAdapter(...)) for automatic cleanup
• Pass structured data as keyword arguments for filtering
• Use separate contexts per subsystem for independent log level control
• Integrate with Python's standard logging via DLTLoggingHandler

Performance Considerations

• DLT overhead: ~1 microsecond per log message (shared memory transport)
• File I/O is buffered; messages may be lost on crash without flush
• Use log level filtering to reduce volume in production
• Rotate log files to prevent disk exhaustion (configure max file/total size)

Best Practices

• Use meaningful 4-character IDs: ADAS (not APP1), CTRL (not CTX1)
• Set production log level to INFO or WARN (not DEBUG/VERBOSE)
• Always close DLT adapters to flush buffered messages
• Use DLT Viewer's filter and search for efficient log analysis
• Archive DLT files with ECU ID and timestamp for traceability
• Correlate DLT logs with CAN traces and diagnostic sessions for RCA