Add ProcessedSignal to ophyd devices

[cappel89]

Summary

This PR introduces an implementation for a ProcessedSignal as well as an alternative to write PseudoMotors in BEC.

ProcessedSignals

ProcessedSignals can either be implemented by having a fully defined config passed to the initialization or similar to the implementation here, where string arguments are used to look for the respective signal/devices in the devicemanager of BEC. Device references must be given as dotted names, and the signal will subscribe to the _default_sub of the given object. The compute method will receive the objects and can in return compute/calculate whatever it desires with the given object. However, upon connecting we will test that the return_value matches the type specified in the model for the signal.

Virtual Motors

Using the processed signals, a PSIPseudoMotor base class is introduced. It relies on the signals and uses them to generate a pseudo motor interface with at least readback/user_readback, setpoint/user_setpoint and motor_is_moving. A center and width implementation is introduced to devices, whereas an example for an alternative integration for a center based on sub-signals is shown here.

Note

• Test will be added later today. Code is already ready to review.

To test

You may add the following devices to your demo_config.yaml to test the implementation.

sl5width:
  readoutPriority: baseline
  deviceClass: ophyd_devices.devices.virtual_slit.VirtualSlitWidth
  deviceConfig:
    left_slit: sl5trxi
    right_slit: sl5trxo
  enabled: true
  readOnly: false
  needs:
    - sl5trxi
    - sl5trxo

sl5center:
  readoutPriority: baseline
  deviceClass: ophyd_devices.devices.virtual_slit.VirtualSlitCenter
  deviceConfig:
    left_slit: sl5trxi
    right_slit: sl5trxo
  enabled: true
  readOnly: false
  needs:
    - sl5trxi
    - sl5trxo

slitcenter:
  readoutPriority: baseline
  deviceClass: ophyd_devices.sim.sim_test_devices.VirtualSlitCenter
  enabled: true
  readOnly: false

pseudosignal:
  readoutPriority: monitored
  deviceClass: ophyd_devices.sim.sim_test_devices.BECPseudoSignal
  deviceConfig:
    signal_1: bpm4i
    signal_2: bpm5i
  enabled: true
  readOnly: false
  needs:
    - bpm4i
    - bpm5i

pseudodevicesignal:
  readoutPriority: monitored
  deviceClass: ophyd_devices.sim.sim_test_devices.BECPseudoSignal
  deviceConfig:
    signal_1: samx.readback
    signal_2: samy.readback
  enabled: true
  readOnly: false
  needs:
    - samx
    - samy

[codecov]

Codecov Report

❌ Patch coverage is 29.87421% with 223 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
ophyd_devices/utils/bec_processed_signal.py	26.66%	77 Missing ⚠️
ophyd_devices/devices/virtual_slit.py	0.00%	66 Missing ⚠️
...s/interfaces/base_classes/psi_pseudo_motor_base.py	31.11%	62 Missing ⚠️
ophyd_devices/sim/sim_test_devices.py	44.82%	16 Missing ⚠️
ophyd_devices/sim/sim_signals.py	92.59%	2 Missing ⚠️

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[Copilot]

Pull request overview

This PR introduces a new BECProcessedSignal class that computes its value based on signals from other devices in BEC's device manager, along with supporting changes to sim signals to properly trigger subscription callbacks.

Changes:

• Added ophyd_devices/devices/processed_signal.py with ProcessedSignalModel (Pydantic config model), DeviceSignalMapping, and BECProcessedSignal (a read-only ophyd signal that subscribes to other device signals and computes a derived value via a user-defined function).
• Modified SetableSignal.get() and ReadOnlySignal.get() in sim_signals.py to update _readback and fire _run_subs on every get() call, enabling subscription-based updates needed by BECProcessedSignal.
• Removed an unused BECDeviceBase import and a commented-out line from sim_signals.py.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 6 comments.

File	Description
ophyd_devices/devices/processed_signal.py	New module defining BECProcessedSignal — a signal that computes its value from other device signals via a configurable model. Includes validation, subscription management, and an example __main__ block.
ophyd_devices/sim/sim_signals.py	Updates SetableSignal.get() and ReadOnlySignal.get() to properly set _readback and trigger _run_subs callbacks; removes unused import and dead code.

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[d-perl]

This looks great! I am basically okay with this implementation, I think it should work well, but I had a crazy idea about how to change it a bit which I would like your feedback on:

• is it important that the model can be dynamically changed? if not, I would consider just requiring it on init and getting rid of set_model, but if it's important, then set_model should refresh the things set up in the connection (see comments in code)
  • to make that work with the pseudopositioner I think it should be possible if the model devices could be a dict[str, str] | Callable[[BECProcessedSignal], dict[str, str]] which would be called explicitly with the signal self before get_device_objects_from_device_manager in wait_for_connection
  • this could then do signal.parent.get_positioner_objects in PSIPseudoMotorBase to keep the simple reference by device name in the concrete subclasses

I think the tradeoff is that creating base classes like the PSIPseudoMotorBase becomes a bit more complicated, but we remove some potential sources of runtime errors and making the subclasses like the VirtualSlitCenter would be even a tiny bit simpler