MATLAB Vehicle Network Communication

Prerequisites

• MATLAB R2021a or later
• Vehicle Network Toolbox installed (ver('vnt') to verify)
• For physical hardware: vendor-specific drivers installed (Vector CANlib, Kvaser CANlib, NI-XNET, PEAK PCAN driver)
• For testing without hardware: MathWorks Virtual channels are always available

Overview

Guide Claude through helping users establish vehicle network communication using MATLAB Vehicle Network Toolbox. This skill covers the full workflow from hardware discovery to message exchange across all supported protocols and vendors.

Implemented protocols:

• CAN / CAN FD — fully documented

Planned protocols (architecture ready, not yet documented):

• J1939 — parameter groups, transport protocol, address claiming
• XCP — measurement, calibration, A2L file handling
• Additional protocols as VNT adds support

When to Use

• User wants to send/receive messages on a vehicle network bus in MATLAB
• User is setting up a communication test bench or loopback verification
• User asks about Vehicle Network Toolbox channel configuration
• User encounters channel errors (initialization access, bus speed, no acknowledgment)
• User wants to filter, decode, or analyze vehicle network messages
• User asks which hardware works on their platform
• User wants passive bus monitoring without affecting traffic
• User needs to encode/decode signal data from messages

When NOT to Use

• User wants to log/replay BLF files without live communication — use a BLF logging skill
• User is building Simulink vehicle network blocks — use Simulink-specific skills
• User needs CAN database file (DBC/LDF/A2L) creation or editing — this skill covers using existing files only
• User is working with a protocol not yet documented in this skill (check protocol sections below)

Protocol Router

Use this decision tree to identify which protocol the user needs:

If the user asks about a protocol not yet documented, inform them which protocols are currently covered and offer to help with those.

Shared Concepts (All Protocols)

Hardware Discovery

t = canChannelList;  % CAN/CAN FD/J1939 devices

All VNT protocols share the same hardware discovery mechanism. See references/shared/hardware-discovery.md.

Channel Lifecycle

All protocols follow the same lifecycle pattern:

Create Channel → Configure → Start → Operate → Stop/Cleanup

Key rules:

• Configuration (bus speed, filters) must happen BEFORE start
• clear ch releases the channel (equivalent to stop + destroy)
• Use onCleanup(@() stop(ch)) for error-safe cleanup
• Running channels hold InitializationAccess — blocking new channel creation

See references/shared/channel-lifecycle.md.

Vendor / Platform Matrix

CAN / CAN FD

Troubleshooting Gate

If the user reports a CAN/CAN FD problem — "not working", "trouble", "error", "can't connect", "no messages", hardware not detected, or any communication failure — you MUST do one of the following:

1. Domain-knowledge question ("why does X cause Y", "what's the maximum stub length for CAN FD", "explain bit rate switching") — answer from references/can/troubleshooting/l1-domain-knowledge.md without running diagnostics.

2. Actionable problem requiring diagnosis — Load references/can/troubleshooting/diagnostic-workflow.md BEFORE responding. Follow its Entry-Point Routing to select the correct starting step. Do NOT diagnose from this file. The tables, pitfalls, and patterns below are reference material for healthy operation — they are NOT a diagnostic procedure. Improvising from them produces wall-of-text responses with multiple guesses instead of structured one-question-at-a-time triage.

Core Workflow

digraph can_workflow {
    rankdir=TB;
    node [shape=box];

    discover [label="1. Discover Hardware\ncanChannelList"];
    decide [label="CAN Classic or CAN FD?" shape=diamond];
    create_classic [label="2a. Create Channel\ncanChannel(vendor, device, ch)"];
    create_fd [label="2b. Create FD Channel\ncanChannel(..., ProtocolMode='CAN FD')\nor canFDChannel(...)"];
    config [label="3. Configure Bus Speed\nconfigBusSpeed (vendor-specific syntax)"];
    start [label="4. Start Channel\nstart(ch)"];
    operate [label="5. Transmit / Receive\ntransmit, receive\ntransmitPeriodic, transmitEvent, replay"];
    cleanup [label="6. Cleanup\nstop(ch) or clear ch"];

    discover -> decide;
    decide -> create_classic [label="Classic"];
    decide -> create_fd [label="CAN FD"];
    create_classic -> config;
    create_fd -> config;
    config -> start;
    start -> operate;
    operate -> cleanup;
}

Post-Transmit Verification (MANDATORY)

After ANY transmit, verify the bus accepted the frame before reporting success:

pause(0.5);
fprintf('TEC=%d REC=%d BusStatus=%s\n', ch.TransmitErrorCount, ch.ReceiveErrorCount, ch.BusStatus);

Never claim "sent successfully" from transmit returning without error. It is non-blocking and returns immediately regardless of bus state. When routing to diagnostics, do NOT list multiple possible causes — let Step 0.5 identify the root cause and ask one targeted question.

CAN Classic vs CAN FD Decision

Critical Patterns (Non-Obvious API Behavior)

These patterns are where the API behaves differently than expected. Follow these exactly.

attachDatabase operates on MESSAGES, not channels

% WRONG — will error
attachDatabase(ch, db);
ch.Database = db;  % only valid for name-based filterAllowOnly

% CORRECT — attach to received message object
rxMsg = receive(ch, 1);
attachDatabase(rxMsg, db);
speed = rxMsg.Signals.EngineSpeed;

transmitPeriodic + pack for live signal updates

% WRONG — manual loop blocks MATLAB, timing is inaccurate
while running
    pack(msg, newValue, 0, 16, 'LittleEndian');
    transmit(ch, msg);
    pause(0.1);
end

% CORRECT — hardware-timed, non-blocking
transmitPeriodic(ch, msg, 'On', 0.1);
start(ch);
pack(msg, newValue, 0, 16, 'LittleEndian');  % next cycle sends updated data

filterAllowOnly REQUIRES type argument for numeric IDs

% WRONG — errors with "Expected NAME to be one of these types: char, cell"
filterAllowOnly(ch, [0x180 0x181]);

% CORRECT — must specify 'Standard' or 'Extended'
filterAllowOnly(ch, [0x180 0x181], 'Standard');
filterAllowOnly(ch, [0x18FEF100], 'Extended');

CAN FD configBusSpeed is vendor-specific

% MathWorks Virtual / NI — simple 3-arg form works
configBusSpeed(ch, 500000, 2000000);

% Vector / Kvaser — REQUIRES 9-arg advanced timing form
configBusSpeed(ch, 500000, 2, 6, 3, 2000000, 2, 6, 3);

% PEAK-System — REQUIRES 10-arg clock-based form
configBusSpeed(ch, 20, 5, 1, 2, 1, 2, 1, 3, 1);

CAN FD receive ALWAYS returns timetable

% CAN FD channels ignore OutputFormat — always timetable
msgs = receive(fdCh, Inf);       % returns timetable
msgs.ID                          % numeric vector of IDs
msgs.Data{1}                     % uint8 vector for first message
% WRONG: msgs(1).Data, msgs.Data(1) — these error on timetable

transmitEvent fires on ANY .Data write (including pack)

transmitEvent(ch, msg, 'On');
start(ch);
pack(msg, value, 0, 16, 'LittleEndian');  % this auto-transmits!
% No explicit transmit() call needed — pack triggers it

Common Pitfalls

CAN References

Detailed API documentation (load on demand):

• references/can/channel-creation.md — canChannel, canFDChannel, vendor-specific syntax
• references/can/bus-speed-config.md — configBusSpeed, vendor-specific argument counts
• references/can/message-creation.md — canMessage, canFDMessage, valid FD DLCs
• references/can/transmit.md — transmit, transmitPeriodic, transmitEvent, replay
• references/can/receive.md — receive, SilentMode, timetable output, FIFO behavior
• references/can/filters.md — filterAllowOnly, filterBlockAll, filterAllowAll
• references/can/database.md — canDatabase, attachDatabase, signal-level decode/encode
• references/can/pack-unpack.md — pack, unpack, signal extraction, byte-order
• references/can/message-extraction.md — extractAll, extractRecent, extractTime, discard

CAN Troubleshooting

See Troubleshooting Gate at the top of this section. Also route to diagnostics when the agent observes unhealthy bus state (TEC/REC > 0, BusStatus not ErrorActive) during any operation — including after transmit verification.

• references/can/troubleshooting/diagnostic-workflow.md — Full diagnostic procedure (Phase 0 automation, L1 physical, L2 traffic analysis)
• references/can/troubleshooting/script-interfaces.md — Function signatures, arguments, and outputs for all diagnostic/analysis scripts

Shared References

• references/shared/hardware-discovery.md — canChannelList, platform constraints
• references/shared/channel-lifecycle.md — start, stop, onCleanup, channel release
• references/shared/limitations.md — Vendor/platform-specific constraints

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