Interfaces

The Lightpath application depends on an a specific API for devices. For maximum flexibility, and in order to avoid duplicating object implementations, any object can be entered into the path as long as it agrees with one of the interfaces below.

The LightInterface covers the majority of LCLS devices. The logical implementation of reading PVs and updating the reported state of the device is up to the object to implement, the lightpath will count on these functions to be accurate in order to determine the state of the beamline as a whole. The LightInterface simplifies a device down to one of two states, inserted and removed. If a device is not found in either of these states it is considered unknown and a possible impediment to the path. There are a number of devices that are regularly inserted into the beamline that do not block photons completely such as IPIMB targets and attenutators. These devices are incorporated by adjusting the LightInterface.transmission, either to a fixed value or one which depends on other device readbacks. The only type of devices that require a more copmlex interface are those that have the potential that mark the transition from one beamline to another. These device will use the BranchingInterface. This includes mirrors and crystals that different hutches use to manipulate from the common line.

Device Interfaces

class pcdsdevices.interface.LightInterface

Interface for a basic lightpath device

beamline

Specific beamline the device is on

inserted

Report if the device is currently inserted into the beam

removed

Report if the device is currently removed from the beam

subscribe(cb, event_type=None, run=False, **kwargs)

Subscribe a callback function to run when the device changes state

Parameters:

• cb (callable) – Function to be run upon change
• event_type (str, optional) – Type of event the function will be called after
• run (bool, optional) – Run the callable immediately or wait for an event.

transmission

Approximate transmission percentage of X-rays through device. Most devices will have 0.0 transmission, as in they block the beam completely

z

Z position along the beamline in meters

class pcdsdevices.interface.BranchingInterface

Bases: pcdsdevices.interface.LightInterface

Interface for a branching device

branches

List of possible beamlines the device is available to send photons

destination

Current destinations of the branching device. Should always be returned as a list to accomodate branches that can send beam to multiple positions

MPS Interface

class pcdsdevices.interface.MPSInterface

Interface for MPS device

The lightpath surveys devices for an attribute mps. It is expected that if a device is in the MPS system, this attribute will return a sub-device that uses this interface

bypassed

Bypass state of the MPS bit

faulted

Boolean of whether MPS is faulted or not

veto_capable

Whether the device causes downstream faults to be ignored