Markus Zolliker
da15df076a
- before some chamges in the gerrit pipline Change-Id: I33eb2d75f83345a7039d0fb709e66defefb1c3e0
100 lines
4.2 KiB
ReStructuredText
100 lines
4.2 KiB
ReStructuredText
Coding
|
|
======
|
|
|
|
.. _class_coding:
|
|
|
|
Coding a Class for a SECoP Module
|
|
---------------------------------
|
|
|
|
A SECoP module is represented as an instance of a python class.
|
|
For programming such a class, typically you create a
|
|
subclass of one of the base classes :class:`Readable <frappy.modules.Readable>`,
|
|
:class:`Writable <frappy.modules.Writable>` or :class:`Drivable <frappy.modules.Drivable>`.
|
|
It is also quite common to inherit from classes created for similar modules,
|
|
and or to inherit from a mixin class like :class:`HasIO <frappy.io.HasIO>`.
|
|
|
|
For creating the :ref:`parameters <module structure parameters>`,
|
|
class attributes are used, using the name of
|
|
the parameter as the attribute name and an instantiation of :class:`frappy.params.Parameter`
|
|
for defining the parameter. If a parameter is already given by an inherited class,
|
|
the parameter declaration might be omitted, or just its altered properties
|
|
have to be given.
|
|
|
|
In addition, you might need one or several configurable items
|
|
(see :ref:`properties <module structure properties>`), declared in the same way, with
|
|
``<property name> =`` :class:`frappy.params.Property` ``(...)``.
|
|
|
|
For each of the parameters, the behaviour has to be programmed with the
|
|
following access methods:
|
|
|
|
def read\_\ *<parameter>*\ (self):
|
|
Called on a ``read`` SECoP message and whenever the internal poll mechanism
|
|
of Frappy tries to get a new value. The return value should be the
|
|
retrieved value.
|
|
This method might also be called internally, in case a fresh value of
|
|
the parameter is needed.
|
|
|
|
.. admonition:: polling
|
|
|
|
The Frappy framework has a built in :ref:`polling <polling>` mechanism,
|
|
which calls above method regularely. Each time ``read_<parameter>`` is
|
|
called, the Frappy framework ensures then that the value of the parameter
|
|
is updated and the activated clients will be notified by means of an
|
|
``update`` message.
|
|
|
|
def write\_\ *<parameter>*\ (self, value):
|
|
Called on a ``change`` SECoP message. The ``value`` argument is the value
|
|
given by the change message, and the method should implement the change,
|
|
typically by handing it over to the hardware. On success, the method must
|
|
return the accepted value. If the value may be read back
|
|
from the hardware, the readback value should be returned, which might be
|
|
slighly altered for example by rounding. The idea is, that the returned
|
|
value would be the same, as if it would be done by the ``read_<parameter>``
|
|
method. Often the easiest implementation is just returning the result of
|
|
a call to the ``read_<parameter>`` method.
|
|
|
|
.. admonition:: behind the scenes
|
|
|
|
Assigning a parameter to a value by setting the attribute via
|
|
``self.<param> = <value>`` or ``<module>.<param> = <value>`` includes
|
|
a :ref:`type check <type check>`, some type conversion and ensures that
|
|
a :ref:`notification <client notification>` with an
|
|
``update`` message is sent to all activated clients.
|
|
|
|
Example code:
|
|
|
|
.. code:: python
|
|
|
|
from frappy.core import HasIO, Drivable, Property, Parameter, StringType
|
|
|
|
class TemperatureLoop(HasIO, Drivable):
|
|
"""a temperature sensor with loop"""
|
|
# internal property to configure the channel
|
|
channel = Property('the Lakeshore channel', datatype=StringType())
|
|
# modifying a property of inherited parameters (unit is propagated to the FloatRange datatype)
|
|
value = Parameter(unit='K')
|
|
target = Parameter(unit='K')
|
|
|
|
def read_value(self):
|
|
# using the inherited HasIO.communicate method to send a command and get the reply
|
|
reply = self.communicate(f'KRDG?{self.channel}')
|
|
return float(reply)
|
|
|
|
def read_status(self):
|
|
... determine the status from the hardware and return it ...
|
|
return status_code, status_text
|
|
|
|
def read_target(self):
|
|
... read back the target value ...
|
|
return target
|
|
|
|
def write_target(self, target):
|
|
... write here the target to the hardware ...
|
|
# important: make sure that the status is changed to BUSY within this method:
|
|
self.status = BUSY, 'target changed'
|
|
return self.read_target() # return the read back value
|
|
|
|
|
|
|
|
.. TODO: io, state machine, persistent parameters, rwhandler, datatypes, features, commands, proxies
|