Channels

A channel is a named, typed stream of samples. The [channels."name"] tables map raw source data — a Protobuf field, an MQTT topic, an Influx field — onto channels you can drop on panels. The channel registry built from these tables is what the whole app reasons about; panels resolve channel names to ids through it and never parse names themselves.

A Protobuf channel

For a ZeroMQ/Protobuf source you declare which message field carries the value and which carries the timestamp:

[channels."sensor.acceleration.x"]
topic      = "accel"                       # source topic this field arrives on
proto_path = "AccelBatch.samples.x"        # value field path in the proto
ts_path    = "AccelBatch.samples.t_ns"     # timestamp field path (nanoseconds)
type       = "float"                       # float | int | bool | text
unit       = "m/s²"
color      = "#ff0000"
max_rate   = 100000                        # Hz — used to size the ring buffer
history_s  = 10.0                           # seconds of history retained
eu_scale   = 1.0                            # raw → engineering-unit scale
eu_offset  = 0.0                            # raw → engineering-unit offset

Fields

Field	Required	Meaning
`topic`	yes	Source topic/subject the data arrives on
`proto_path`	proto sources	Dotted path to the value field in the message
`ts_path`	proto sources	Dotted path to the nanosecond timestamp field
`type`	yes	Sample type: `float`, `int`, `bool`, or `text`
`unit`	no	Display unit label
`color`	no	`#rrggbb` line/marker colour
`max_rate`	no	Expected sample rate in Hz; sizes the ring buffer
`history_s`	no	Seconds of history kept in the live ring
`eu_scale` / `eu_offset`	no	Engineering-unit scaling applied on ingest
`max_lines`	text only	Max retained log lines for `type = "text"`

Ring-buffer capacity is derived as max_rate × history_s × 1.2. If you omit max_rate / history_s, per-channel values fall back to the file-wide [defaults] (or the built-in 1000 Hz / 10.0 s).

Sample types

`type`	Rust type	Typical panels
`float`	`f64`	waveform, gauge, FFT, XY
`int`	`i64`	waveform, state graph, status
`bool`	boolean	waveform, state graph, status
`text`	string (log line)	log, status

A state / integer channel

[channels."motor.state"]
topic      = "status"
proto_path = "StatusBatch.samples.state"
ts_path    = "StatusBatch.samples.t_ns"
type       = "int"
max_rate   = 1000
history_s  = 30.0

A text / log channel

[channels."system.log"]
topic      = "log"
proto_path = "LogBatch.samples.message"
ts_path    = "LogBatch.samples.t_ns"
type       = "text"
max_lines  = 500

Engineering-unit scaling

eu_scale and eu_offset convert a raw source value into engineering units on ingest, before it reaches the store: eu = raw × eu_scale + eu_offset. Everything downstream — panels, cursors, recordings — sees the scaled value.

Channels without a proto path

Not every source needs proto_path / ts_path:

MQTT / WebSocket channels can be discovered at runtime — a topic dragged onto a panel — and never appear in config.toml at all. See MQTT and WebSocket.
Bridge channels declare only topic + sample_type, because the bridge's payload schema is fixed and built in. See Bridge Adapters.

Constraint: topic names must be unique across coexisting sources. A bridge and a ZeroMQ source cannot both emit topic accel — they share one registry.

datavis — User Guide