Telemetry Events Reference

BB emits :telemetry events for performance monitoring and diagnostics.

Event Types

Span Events

Span events use :telemetry.span/3 which automatically emits:

• [:prefix, :start] - When operation begins
• [:prefix, :stop] - When operation completes successfully
• [:prefix, :exception] - When operation raises

Diagnostic Events

Single events emitted for component health reporting.

Motion Events

[:bb, :motion, :solve]

IK solver execution.

Start Measurements:

Stop Measurements:

Metadata:

Stop Metadata (additional):

[:bb, :motion, :move_to]

Full move operation (solve + send positions).

Stop Measurements:

Metadata:

[:bb, :motion, :send_positions]

Sending positions to actuators.

Stop Measurements:

Metadata:

Kinematics Events

[:bb, :kinematics, :forward]

Forward kinematics computation.

Stop Measurements:

Metadata:

Command Events

[:bb, :command, :execute]

Command execution span.

Stop Measurements:

Metadata:

Estimator Events

[:bb, :estimator, :input]

Counter emitted each time a BB.Estimator server receives a message on one of its declared input paths.

Measurements:

Metadata:

[:bb, :estimator, :output]

Counter emitted each time a BB.Estimator server publishes an output message (one per {output_name, message} returned from a callback).

Measurements:

Metadata:

[:bb, :estimator, :latency]

Duration from a driver-input message arriving to the estimator emitting its output(s). Useful for monitoring estimator performance and tuning latency_budget.

Measurements:

Metadata:

[:bb, :estimator, :dropped]

Counter emitted when a dispatch is dropped instead of fired. Currently emitted only for :sync_miss (multi-input fan-in: a non-driver input older than sync_tolerance).

Measurements:

Metadata:

[:bb, :estimator, :transition]

Counter emitted on every health state transition. Fires whether or not an on_* command is configured — observability is independent of policy.

Measurements:

Metadata:

Diagnostic Events

[:bb, :diagnostic]

Component health diagnostic.

Measurements: Empty (%{})

Metadata: BB.Diagnostic struct

See BB.Diagnostic module for diagnostic event details.

Subscribing to Events

Single Event

:telemetry.attach(
  "my-handler",
  [:bb, :motion, :solve, :stop],
  &MyApp.handle_solve_complete/4,
  nil
)

Multiple Events

:telemetry.attach_many(
  "my-perf-handler",
  [
    [:bb, :motion, :solve, :stop],
    [:bb, :motion, :move_to, :stop],
    [:bb, :command, :execute, :stop]
  ],
  &MyApp.handle_perf_event/4,
  nil
)

Handler Example

defmodule MyApp.TelemetryHandler do
  require Logger

  def handle_event([:bb, :motion, :solve, :stop], measurements, metadata, _config) do
    duration_ms = System.convert_time_unit(measurements.duration, :native, :millisecond)

    Logger.info(
      "IK solve for #{metadata.robot} completed in #{duration_ms}ms " <>
      "(#{metadata.iterations} iterations, residual: #{metadata.residual})"
    )
  end

  def handle_event([:bb, :motion, :solve, :exception], _measurements, metadata, _config) do
    Logger.error("IK solve for #{metadata.robot} failed")
  end
end

Converting Duration

Durations are in native time units. Convert for display:

# To milliseconds
duration_ms = System.convert_time_unit(duration, :native, :millisecond)

# To microseconds (for high-precision)
duration_us = System.convert_time_unit(duration, :native, :microsecond)

Emitting Custom Events

Use BB.Telemetry helpers:

# Span (start/stop automatically)
BB.Telemetry.span([:bb, :custom, :operation], %{robot: MyRobot.Robot}, fn ->
  result = do_work()
  {result, %{items_processed: 10}}
end)

# Single event
BB.Telemetry.emit([:bb, :custom, :event], %{count: 1}, %{robot: MyRobot.Robot})

Metrics Collection

Example with telemetry_metrics and telemetry_poller:

# In your application supervision tree
children = [
  {Telemetry.Metrics.ConsoleReporter, metrics: metrics()}
]

defp metrics do
  [
    Telemetry.Metrics.distribution(
      "bb.motion.solve.duration",
      event_name: [:bb, :motion, :solve, :stop],
      measurement: :duration,
      unit: {:native, :millisecond},
      tags: [:robot, :solver]
    ),
    Telemetry.Metrics.counter(
      "bb.command.execute.count",
      event_name: [:bb, :command, :execute, :stop],
      tags: [:robot, :command]
    )
  ]
end

Event Naming Convention

BB follows the telemetry naming convention:

[:bb, :subsystem, :operation]
[:bb, :subsystem, :operation, :start]
[:bb, :subsystem, :operation, :stop]
[:bb, :subsystem, :operation, :exception]

Subsystems:

• motion - Motion planning and execution
• kinematics - Kinematic computations
• command - Command system
• estimator - State estimators (BB.Estimator)
• diagnostic - Health diagnostics