lab-nidaq-mcp

NI-DAQmx instrument backend for lab-executor-mcp. Version 0.1 supports software-timed, single-point analog input, digital input, analog output, and digital output on the agreed USB-6009 and USB-6210 devices. Waveforms, streaming, triggers, counters, and timers are out of scope.

Resources are device-level and case-sensitive: DAQ::Dev1 and DAQ::Dev2. Commands select a channel:

READ AI ai0
READ DI port0/line0
INFO model
WRITE AO ao0 2.5
WRITE DO port1/line0 1
SAFE

Safety model

Outputs are disabled unless explicitly declared in configuration. Every declared output requires an explicit safe_value; the software never assumes zero is safe. A configured interlock is read immediately before every ordinary output write, and a mismatch or read failure refuses the write. Safe-value writes from SAFE and close() deliberately bypass the interlock and attempt every declared output. Analog output values are checked against both the declared range and the model capability before a DAQmx task is created. Writes are never automatically retried.

Mandatory installation requirement (D9)

The USB-6009 and USB-6210 cannot be assigned a programmable power-up output state. Software therefore cannot guarantee an output level after a host crash, USB disconnection, or loss of host control. The installer is responsible for wiring the external circuit so that a high-impedance output line is the safe state. This is an installation requirement, not a guarantee made by this backend. support_level remains experimental until output operation and this wiring requirement are verified on the installed hardware.

Configuration

devices:
  Dev2:
    model: "USB-6009"
    interlock: none
    analog_inputs:
      ai0: {range: [-10, 10]}
    analog_outputs:
      ao0:
        range: [0, 5]
        safe_value: 0.0
    digital_outputs:
      port1/line0:
        safe_value: 0

model and interlock are mandatory. The declared model selects physical capabilities and must match the DAQmx product_type read on first hardware access. Use the explicit interlock string none, or configure {line: "port0/line7", require: 1}. An interlock line cannot also be declared as an output.

lab-nidaq --config nidaq.yaml --dry-run
lab-nidaq --config nidaq.yaml

The entry point is lab_executor.backends: nidaq, with routing prefix DAQ::.

Measured hardware limits

The capability table's maximum sample rate is the device's specified figure. It is not a guarantee that a given host can sustain it, and this backend does not pretend otherwise: a rate the hardware cannot keep up with surfaces as a transport error carrying DAQmx's own diagnosis, rather than silently returning short or duplicated data.

Measured on this hardware on 2026-07-20:

• USB-6210 at 250 kS/s — 10,000 samples acquired without error.
• USB-6009 at its specified 48 kS/s maximum — DAQmx reports Onboard device memory overflow (-200361). The device has little onboard memory and transfers over interrupts, so the specified maximum is not reachable for buffered reads on this host. 10 kS/s was reliable.

An unconnected differential input rails rather than reading zero. A USB-6210 input with nothing attached returned a constant 10.974836 V across all 10,000 samples, while a USB-6009 single-ended input on the same code path returned genuine ADC noise (9 distinct values, σ≈2.2 mV). Constant data from an acquisition usually means the terminal is floating, not that acquisition failed; bias unused differential inputs to AI GND if you need a meaningful reading.

Development

Tests use only MockNiDaqBackend; they never construct a DAQmx task. Run:

python -m pytest -q
python -m ruff check src tests
python -m ruff format --check src tests
python -m build

License

MIT