Demo: Generate Frames and Watch with Candump¶

This demo shows how to use canarchy generate to produce test CAN traffic and canarchy capture --candump to watch it arrive in real time.

You need two terminals.

Set the backend once¶

The cleanest option is a persistent user config file. Create ~/.canarchy/config.toml:

[transport]
backend = "python-can"
interface = "udp_multicast"

Every canarchy command in any terminal will pick this up automatically — no per-session setup needed.

If you prefer environment variables instead, export them at the top of each terminal:

export CANARCHY_TRANSPORT_BACKEND=python-can
export CANARCHY_PYTHON_CAN_INTERFACE=udp_multicast

Backend choice matters¶

Two backends are available for software-only loopback:

Backend	Cross-process?	macOS?	Linux?	Requires
`virtual`	No — in-process only	Yes	Yes	nothing
`udp_multicast`	Yes	Yes*	Yes	`msgpack`, multicast route

virtual does not work for this demo. It uses an in-process shared queue, so frames sent in one process are invisible to a capture running in a separate terminal. Use udp_multicast for the two-terminal workflow shown here.

* macOS requires a multicast route to 239.0.0.0/8. If you see "No route to host", run:
sudo route add -net 239.0.0.0/8 -interface lo0

Terminal 1 — Start the Candump Capture¶

canarchy capture 239.0.0.1 --candump

The terminal blocks and waits. Each arriving frame prints as a candump-style line.

Terminal 2 — Generate Frames¶

If your ~/.canarchy/config.toml enables [safety].require_active_ack = true, add --ack-active and reply YES when prompted before the transmit step begins.

Random frames¶

canarchy generate 239.0.0.1 --count 5

Terminal 1 prints something like:

(1713369600.000000) 239.0.0.1 2A1#C3F19E04
(1713369600.200000) 239.0.0.1 05B#00
(1713369600.400000) 239.0.0.1 71C#A8B2CC07F1
(1713369600.600000) 239.0.0.1 3F0#
(1713369600.800000) 239.0.0.1 4D2#119A

Fixed ID and payload¶

canarchy generate 239.0.0.1 --id 0x7DF --dlc 3 --data DEADBE --count 3

Terminal 1 prints:

(1713369600.000000) 239.0.0.1 7DF#DEADBE
(1713369600.200000) 239.0.0.1 7DF#DEADBE
(1713369600.400000) 239.0.0.1 7DF#DEADBE

Incrementing data¶

--data I produces a rolling byte pattern useful for spotting dropped or out-of-order frames:

canarchy generate 239.0.0.1 --id 0x100 --dlc 4 --data I --count 4

Terminal 1 prints:

(1713369600.000000) 239.0.0.1 100#00010203
(1713369600.200000) 239.0.0.1 100#04050607
(1713369600.400000) 239.0.0.1 100#08090A0B
(1713369600.600000) 239.0.0.1 100#0C0D0E0F

Extended (29-bit) IDs¶

canarchy generate 239.0.0.1 --id 0x18FEEE31 --dlc 8 --data R --extended --count 1

Control the gap¶

--gap sets the inter-frame delay in milliseconds (default 200 ms):

canarchy generate 239.0.0.1 --count 10 --gap 50

Run continuously, `cangen`-style¶

Omit --count to generate and transmit frames continuously, spaced by --gap, until you stop it with Ctrl-C:

canarchy generate 239.0.0.1 --gap 50

Get Structured Output¶

Use --json instead of --candump to get machine-readable output:

canarchy generate 239.0.0.1 --id 0x123 --dlc 4 --data 11223344 --count 2 --json

Stop the Capture¶

Press Ctrl+C in Terminal 1 to stop the candump session.