Caproto Apps

Implementations of select EPICS-compatible records in caproto.

Installation

pip install caproto-apps

Components

Alive

The AliveGroup provides equivalent functionality to the EPICS alive record and is compatible with existing alive daemons.

It is intended to be added to an existing PVGroup using caproto's SubGroup wrapper:

from caprotoapps import AliveGroup

class MyIOC(PVGroup):
    alive = SubGroup(
        AliveGroup,
        prefix="alive",
        remote_host="xapps2.xray.aps.anl.gov",
        remote_port=5678,  # Optional, 5678 is the default port
        ioc_name="my_ioc", # If omitted, will use the parent IOC prefix
    )

if __name__ == "__main__":
    # Start the IOC as normal for caproto
    ...

An alive daemon can request environmental variables from the alive group. Many of the default environmental variables in the EPICS alive record are specific to EPICS (e.g. EPICS_BASE) and so are not included as default environmental variables in this AliveGroup.

Presently, the default environmental variables are:

1. ENGINEER
2. LOCATION
3. GROUP
4. STY
5. PREFIX

Neither caproto nor caproto-apps sets the value of these environmental variables, so it is left up to the launcher for the parent IOC (e.g. in a systemd unit). Additional default environmental variables can be added (or replaced) by subclassing the AliveGroup:

from caprotoapps.alive import AliveGroup, envvar_default_property

class MyAliveGroup(AliveGroup):
    # Replace ``ENGINEER`` with ``SCIENTIST``
    evd1 = envvar_default_property(1, "SCIENTIST")
    # Add a new variable, "STATUS"
    evd6 = envvar_default_property(1, "STATUS")

LabJack

There are a set of PVGroup objects for the T-series data acquisition devices from the LabJack company. They are designed to mimic the LabJack EPICS module, and operate in a similar manner.

There is a group for each supported device, which is currently:

• LabJackT4

though there are plans to support more in the future.

To add support for a LabJack device, include the following in an IOC:

from caprotoapps import LabJackT4

class MyIOC(PVGroup):
    t4_1 = SubGroup(LabJackT4, prefix="T4_1:", identifier="labjack01")
    t4_2 = SubGroup(LabJackT4, prefix="T4_2:", identifier="labjack02")
    t4_sim = SubGroup(LabJackT4, prefix="T4_3:", identifier="-2")

if __name__ == "__main__":
    # Start your IOC as usual
    ...

For a complete example, see examples/labjack_ioc.py.

identifier can be any valid LJM identifier to distinguish a device:

• The hostname of a network-connected device (see note)
• The IP address of a network-connected device
• The USB port of a USB-connected device
• The serial number of a connected device
• The name of a connected device
• "-2" to use the simulated device
• "ANY" to use the first device found (not recommended)

Manager

The ManagerGroup allows for remote management of other IOCs. Currently the only supported style is that of APS beamline controls group. To allow control of an IOC, specify the path to the startup script using the script parameter.

from caproto.server import SubGroup
from caprotoapps import ManagerGroup

class MyIOC(PVGroup):
    ioc_manager = SubGroup(ManagerGroup,
                           script="/path/to/script.sh")

If the script can be reached on another machine via SSH, then the following pattern can also be used, provided that passwordless login is set up (i.e. using ssh-keygen):

class MyIOC(PVGroup):
    ioc_manager = SubGroup(ManagerGroup,
                               script="myuser@myhost:/path/to/script.sh")
```

**Note:** The *console* PV is currently not implemented.

It is possible to limit which IOCs can be started or stopped via an IOC ManagerGroup using the allow_start and allow_stop parameters during initialization:

class MyIOC(PVGroup):
    mission_critical_manager = SubGroup(ManagerGroup,
                                    allow_start=True,
                                    allow_stop=False)

The status PVs startable and stoppable are read-only indicators of whether the IOC can be controlled via this ManagerGroup. Re-starting an IOC requires both allow_start and allow_stop to be true.

Development

To install caproto-apps for development, first clone the github repository:

git clone https://github.com/canismarko/caproto-apps.git

Then run tests with pytest

pytest

Building the Project for PyPI

(venv) $ python -m build
(venv) $ twine check dist/*
(venv) $ twine upload -r testpypi dist/*
(venv) $ twine upload dist/*