.. currentmodule:: sardana.pool.controller .. _sardana-countertimercontroller: ======================================= How to write a counter/timer controller ======================================= This chapter provides the necessary information to write a counter/timer controller in Sardana. .. contents:: Table of contents :depth: 3 :backlinks: entry .. _sardana-countertimercontroller-howto-basics: The basics ---------- An example of a hypothetical *Springfield* counter/timer controller will be build incrementally from scratch to aid in the explanation. By now you should have read :ref:`the general controller basics ` chapter. You should be able to create a CounterTimerController with: - a proper constructor, - add and delete axis methods - get axis state .. code-block:: python import springfieldlib from sardana.pool.controller import CounterTimerController from sardana import State class SpringfieldCounterTimerController(CounterTimerController): def __init__(self, inst, props, *args, **kwargs): super(SpringfieldCounterTimerController, self).__init__(inst, props, *args, **kwargs) # initialize hardware communication self.springfield = springfieldlib.SpringfieldCounterHW() # do some initialization self._counters = {} def AddDevice(self, axis): self._counters[axis] = True def DeleteDevice(self, axis): del self._counters[axis] StateMap = { 1 : State.On, 2 : State.Moving, 3 : State.Fault, } def StateOne(self, axis): springfield = self.springfield state = self.StateMap[ springfield.getState(axis) ] status = springfield.getStatus(axis) return state, status The examples use a :mod:`springfieldlib` module which emulates a counter/timer hardware access library. The :mod:`springfieldlib` can be downloaded from :download:`here `. The Springfield counter/timer controller can be downloaded from :download:`here `. The following code describes a minimal *Springfield* base counter/timer controller which is able to return both the state and value of an individual counter as well as to start an acquisition: .. literalinclude:: sf_ct_ctrl.py :pyobject: SpringfieldBaseCounterTimerController .. _sardana-countertimercontroller-howto-state: Get counter state ~~~~~~~~~~~~~~~~~ To get the state of a counter, sardana calls the :meth:`~sardana.pool.controller.Controller.StateOne` method. This method receives an axis as parameter and should return either: - state (:obj:`~sardana.sardanadefs.State`) or - a sequence of two elements: - state (:obj:`~sardana.sardanadefs.State`) - status (:obj:`str`) The state should be a member of :obj:`~sardana.sardanadefs.State` (For backward compatibility reasons, it is also supported to return one of :class:`PyTango.DevState`). The status could be any string. .. _sardana-countertimercontroller-howto-load: Load a counter ~~~~~~~~~~~~~~ To load a counter with either the integration time or the monitor counts, sardana calls the :meth:`~sardana.pool.controller.Loadable.LoadOne` method. This method receives axis, value and repetitions parameters. For the moment let's focus on the first two of them. Here is an example of the possible implementation of :meth:`~sardana.pool.controller.Loadable.LoadOne`: .. code-block:: python :emphasize-lines: 3 class SpringfieldCounterTimerController(CounterTimerController): def LoadOne(self, axis, value, repetitions, latency): self.springfield.LoadChannel(axis, value) .. _sardana-countertimercontroller-howto-value: Get counter value ~~~~~~~~~~~~~~~~~ To get the counter value, sardana calls the :meth:`~sardana.pool.controller.Readable.ReadOne` method: - at a given frequency during the acquisition to get the still changing result - one more time after the acquisition to collect the final result This method receives an axis as parameter and should return a valid counter value. Sardana notifies the pseudo counters about the new counter value so they can be updated (see :ref:`sardana-pseudocounter-overview` for more details). In case it is not possible to return a valid counter value you should raise an exception indicating the reason. For example: - during the acquisition the hardware does not provide the still changing value (returning `None` is deprecated since version 3.4) - after the acquisition the final result is invalid e.g. the data format is incorrect - a hardware failure was detected Here is an example of the possible implementation of :meth:`~sardana.pool.controller.Readable.ReadOne`: .. code-block:: python :emphasize-lines: 3 class SpringfieldCounterTimerController(CounterTimerController): def ReadOne(self, axis): try: return self.springfield.getValue(axis) except Exception as e: raise Exception("Problem when reading value") from e .. _sardana-countertimercontroller-howto-start: Start a counter ~~~~~~~~~~~~~~~ When an order comes for sardana to start a counter, sardana will call the :meth:`~sardana.pool.controller.Startable.StartOne` method. This method receives an axis as parameter. The controller code should trigger the hardware acquisition. Here is an example of the possible implementation of :meth:`~sardana.pool.controller.Startable.StartOne`: .. code-block:: python :emphasize-lines: 3 class SpringfieldCounterTimerController(CounterTimerController): def StartOne(self, axis, value): self.springfield.StartChannel(axis) As soon as :meth:`~sardana.pool.controller.Startable.StartOne` is invoked, sardana expects the counter to be acquiring. It enters a high frequency acquisition loop which asks for the counter state through calls to :meth:`~sardana.pool.controller.Controller.StateOne`. It will keep the loop running as long as the controller responds with ``State.Moving``. If :meth:`~sardana.pool.controller.Controller.StateOne` raises an exception or returns something other than ``State.Moving``, sardana will assume the counter is stopped and exit the acquisition loop. For an acquisition to work properly, it is therefore, **very important** that :meth:`~sardana.pool.controller.Controller.StateOne` responds correctly. .. _sardana-countertimercontroller-howto-stop: Stop a counter ~~~~~~~~~~~~~~ It is possible to stop a counter when it is acquiring. When sardana is ordered to stop a counter acquisition, it invokes the :meth:`~sardana.pool.controller.Stopable.StopOne` method. This method receives an axis parameter. The controller should make sure the desired counter is *gracefully* stopped. Here is an example of the possible implementation of :meth:`~sardana.pool.controller.Stopable.StopOne`: .. code-block:: python :emphasize-lines: 3 class SpringfieldCounterTImerController(CounterTimerController): def StopOne(self, axis): self.springfield.StopChannel(axis) .. _sardana-countertimercontroller-howto-abort: Abort a counter ~~~~~~~~~~~~~~~ In an emergency situation, it is desirable to abort an acquisition *as fast as possible*. When sardana is ordered to abort a counter acquisition, it invokes the :meth:`~sardana.pool.controller.Stopable.AbortOne` method. This method receives an axis parameter. The controller should make sure the desired counter is stopped as fast as it can be done. Here is an example of the possible implementation of :meth:`~sardana.pool.controller.Stopable.AbortOne`: .. code-block:: python :emphasize-lines: 3 class SpringfieldCounterTimerController(CounterTimerController): def AbortOne(self, axis): self.springfield.AbortChannel(axis) .. _sardana-countertimercontroller-howto-advanced: Advanced topics --------------- .. _sardana-countertimercontroller-howto-timermonitor: Timer and monitor roles ~~~~~~~~~~~~~~~~~~~~~~~ Usually counters can work in either of two modes: timer or monitor. In both of them, one counter in a group is assigned a special role to control when the rest of them should stop counting. The stopping condition is based on the integration time in case of the timer or on the monitor counts in case of the monitor. The assignment of this special role is based on the measurement group :ref:`sardana-measurementgroup-overview-configuration`. The controller receives this configuration (axis number) via the controller parameter ``timer`` and ``monitor``. The currently used acquisition mode is set via the controller parameter ``acquisition_mode``. Controller may announce its default timer axis with the :obj:`~sardana.pool.controller.Loadable.default_timer` class attribute. .. _sardana-countertimercontroller-howto-timestamp-value: Timestamp a counter value ~~~~~~~~~~~~~~~~~~~~~~~~~ When you read the value of a counter from the hardware sometimes it is necessary to associate a timestamp with that value so you can track the value of a counter in time. If sardana is executed as a Tango device server, reading the value attribute from the counter device triggers the execution of your controller's :meth:`~sardana.pool.controller.Readable.ReadOne` method. Tango responds with the value your controller returns from the call to :meth:`~sardana.pool.controller.Readable.ReadOne` and automatically assigns a timestamp. However this timestamp has a certain delay since the time the value was actually read from hardware and the time Tango generates the timestamp. To avoid this, sardana supports returning in :meth:`~sardana.pool.controller.Readable.ReadOne` an object that contains both the value and the timestamp instead of the usual :class:`numbers.Number`. The object must be an instance of :class:`~sardana.sardanavalue.SardanaValue`. Here is an example of associating a timestamp in :meth:`~sardana.pool.controller.Readable.ReadOne`: .. code-block:: python import time from sardana.pool.controller import SardanaValue class SpringfieldCounterTimerController(CounterTimerController): def ReadOne(self, axis): return SardanaValue(value=self.springfield.getValue(axis), timestamp=time.time()) If your controller communicates with a Tango device, Sardana also supports returning a :class:`~PyTango.DeviceAttribute` object. Sardana will use this object's value and timestamp. Example: .. code-block:: python class TangoCounterTimerController(CounterTimerController): def ReadOne(self, axis): return self.device.read_attribute("value") .. _sardana-countertimercontroller-howto-mutliple-acquisition: Multiple acquisition synchronization ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ This chapter describes an extended :term:`API` that allows you to better synchronize acquisitions involving more than one counter, as well as optimize hardware communication (in case the hardware interface also supports this). Often it is the case that the experiment/procedure the user runs requires to acquire more than one counter at the same time (see :ref:`sardana-measurementgroup-overview`). Imagine that the user requires counter at axis 1 and counter at axis 2 to be acquired. Your controller will receive two consecutive calls to :meth:`~sardana.pool.controller.Startable.StartOne`: .. code-block:: python StartOne(1) StartOne(2) and each StartOne will probably connect to the hardware (through serial line, socket, Tango_ or EPICS_) and ask the counter to be started. This will do the job but, there will be a slight desynchronization between the two counters because hardware call of counter 1 will be done before hardware call to counter 2. Sardana provides an extended *start acquisition* which gives you the possibility to improve the synchronization (and probably reduce communications) but your hardware controller must somehow support this feature as well. The complete start acquisition :term:`API` consists of four methods: - :meth:`~sardana.pool.controller.Startable.PreStartAll` - :meth:`~sardana.pool.controller.Startable.PreStartOne` - :meth:`~sardana.pool.controller.Startable.StartOne` - :meth:`~sardana.pool.controller.Startable.StartAll` Except for :meth:`~sardana.pool.controller.Startable.StartOne`, the implementation of all other start methods is optional and their default implementation does nothing (:meth:`~sardana.pool.controller.Startable.PreStartOne` actually returns ``True``). So, actually, the algorithm for counter acquisition start in sardana is: .. code-block:: text /FOR/ Each controller(s) implied in the acquisition - Call PreStartAll() /END FOR/ /FOR/ Each controller(s) implied in the acquisition /FOR/ Each counter(s) implied in the acquisition - ret = PreStartOne(counter to acquire, new position) - /IF/ ret is not true /RAISE/ Cannot start. Counter PreStartOne returns False - /END IF/ - Call StartOne(counter to acquire, new position) /END FOR/ /END FOR/ /FOR/ Each controller(s) implied in the acquisition - Call StartAll() /END FOR/ The controllers over which we iterate in the above pseudo code are organized so the master timer/monitor controller is the last one to be called. Similar order of iteration applies to the counters of a given controller, so the timer/monitor is the last one to be called. You can assign the master controller role with the order of the controllers in the measurement group. There is one master per each of the following synchronization modes: :attr:`~sardana.pool.pooldefs.AcqSynch.SoftwareTrigger` and :attr:`~sardana.pool.pooldefs.AcqSynch.SoftwareStart`. This order must be set within the measurement group :ref:`sardana-measurementgroup-overview-configuration`. So, for the example above where we acquire two counters, the complete sequence of calls to the controller is: .. code-block:: python PreStartAll() if not PreStartOne(1): raise Exception("Cannot start. Counter(1) PreStartOne returns False") if not PreStartOne(2): raise Exception("Cannot start. Counter(2) PreStartOne returns False") StartOne(1) StartOne(2) StartAll() Sardana assures that the above sequence is never interrupted by other calls, like a call from a different user to get counter state. Suppose the springfield library tells us in the documentation that: ... to acquire multiple counters at the same time use:: startCounters(seq) Example:: startCounters([1, 2]) We can modify our counter controller to take profit of this hardware feature: .. code-block:: python class SpringfieldCounterTimerController(MotorController): def PreStartAll(self): # clear the local acquisition information dictionary self._counters_info = [] def StartOne(self, axis): # store information about this axis motion self._counters_info.append(axis) def StartAll(self): self.springfield.startCounters(self._counters_info) .. _sardana-countertimercontroller-howto-external-synchronization: External (hardware) synchronization ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The synchronization achieved in :ref:`sardana-countertimercontroller-howto-mutliple-acquisition` may not be enough when it comes to acquiring with multiple controllers at the same time or to executing multiple acquisitions in a row. Some of the controllers can be synchronized on an external hardware event and in this case several important aspects needs to be taken into account. Synchronization type """""""""""""""""""" First of all the controller needs to know which type of synchronization will be used. This is assigned on the measurement group :ref:`sardana-measurementgroup-overview-configuration` level. The controller receives one of the :class:`~sardana.pool.pooldefs.AcqSynch` values via the controller parameter ``synchronization``. The selected mode will change the behavior of the counter after the :meth:`~sardana.pool.controller.Startable.StartOne` is invoked. In case one of the software modes was selected, the counter will immediately start acquiring. In case one of the hardware modes was selected, the counter will immediately get armed for the hardware events, and will wait with the acquisition until they occur. Here is an example of the possible implementation of :meth:`~sardana.pool.controller.Controller.SetCtrlPar`: .. code-block:: python :emphasize-lines: 3 from sardana.pool import AcqSynch class SpringfieldCounterTimerController(CounterTimerController): SynchMap = { AcqSynch.SoftwareTrigger : 1, AcqSynch.SoftwareGate : 2, AcqSynch.SoftwareStart : 3, AcqSynch.HardwareTrigger: 4, AcqSynch.HardwareGate: 5, AcqSynch.HardwareStart: 6 } def SetCtrlPar(self, name, value): super(SpringfieldMotorController, self).SetCtrlPar(name, value) synchronization = SynchMap[value] if name == "synchronization": self.springfield.SetSynchronization(synchronization) Multiple acquisitions """"""""""""""""""""" It is a very common scenario to execute multiple hardware synchronized acquisitions in a row. One example of this type of measurements are the :ref:`sardana-users-scan-continuous`. The controller receives the number of acquisitions via the ``repetitions`` argument of the :meth:`~sardana.pool.controller.Loadable.LoadOne` method. Here is an example of the possible implementation of :meth:`~sardana.pool.controller.Loadable.LoadOne`: .. code-block:: python :emphasize-lines: 3 class SpringfieldCounterTimerController(CounterTimerController): def LoadOne(self, axis, value, repetitions, latency): self.springfield.LoadChannel(axis, value) self.springfield.SetRepetitions(repetitions) return value In order to make the acquisition flow smoothly the synchronizer and the counter/timer controllers needs to agree on the synchronization pace. The counter/timer controller manifest what is the maximum allowed pace for him by means of the ``latency_time`` controller parameter (in seconds). This parameter corresponds to the minimum time necessary by the hardware controller to re-arm for the next acquisition. Here is an example of the possible implementation of :meth:`~sardana.pool.controller.Controller.GetCtrlPar`: .. code-block:: python :emphasize-lines: 3 class SpringfieldCounterTimerController(CounterTimerController): def GetCtrlPar(self, name): if name == "latency_time": return self.springfield.GetLatencyTime() .. warning:: By default, the `~sardana.pool.controller.CounterTimerController` base classes return zero latency time controller parameter. If in your controller you override the :meth:`~sardana.pool.controller.Controller.GetCtrlPar` method remember to always call the super class method as fallback: .. code-block:: python :emphasize-lines: 5 def GetCtrlPar(self, name): if name == "some_par": return "some_val" else: return super().GetCtrlPar(name) In the case of the :attr:`~sardana.pool.pooldefs.AcqSynch.HardwareStart` or :attr:`~sardana.pool.pooldefs.AcqSynch.SoftwareStart` synchronizations the counter/timer hardware *auto* triggers itself during the measurement process. In order to fully configure the hardware and set the re-trigger pace you can use the ``latency`` argument (in seconds) of the :meth:`~sardana.pool.controller.Loadable.LoadOne` method: .. code-block:: python :emphasize-lines: 3 class SpringfieldCounterTimerController(CounterTimerController): def LoadOne(self, axis, value, repetitions, latency): self.springfield.LoadChannel(axis, value) self.springfield.SetRepetitions(repetitions) self.springfield.SetLatency(latency) return value .. _sardana-countertimercontroller-howto-external-synchronization-get-values: Get counter values """""""""""""""""" During the hardware synchronized acquisitions the counter values are usually stored in the hardware buffers. Sardana enters a high frequency acquisition loop after the :meth:`~sardana.pool.controller.Startable.StartOne` is invoked which, apart of asking for the counter state through calls to the :meth:`~sardana.pool.controller.Controller.StateOne` method, will try to retrieve the counter values using the :meth:`~sardana.pool.controller.Readable.ReadOne` method. It will keep the loop running as long as the controller responds with ``State.Moving``. Sardana executes one extra readout after the state has changed in order to retrieve the final counter values. The :meth:`~sardana.pool.controller.Readable.ReadOne` method is used indifferently of the selected synchronization but its return values should depend on it and can be: - a single counter value: either :class:`float` or :obj:`~sardana.sardanavalue.SardanaValue` in case of the :attr:`~sardana.pool.pooldefs.AcqSynch.SoftwareTrigger` or :attr:`~sardana.pool.pooldefs.AcqSynch.SoftwareGate` synchronization - a sequence of counter values: either :class:`float` or :obj:`~sardana.sardanavalue.SardanaValue` in case of the :attr:`~sardana.pool.pooldefs.AcqSynch.HardwareTrigger`, :attr:`~sardana.pool.pooldefs.AcqSynch.HardwareGate`, :attr:`~sardana.pool.pooldefs.AcqSynch.HardwareStart` or :attr:`~sardana.pool.pooldefs.AcqSynch.SoftwareStart` synchronization. However, in the second case we may find that some calls to the hardware do not return new values (because with these types of synchronizations Sardana doesn't explicitly control the data acquisition). In this situation you should return an empty sequence `[]`. You should still raise an exception if a hardware failure occurs, the data format is incorrect or an unexpected behaviour is detected. Sardana assumes that the counter values are returned in the order of acquisition and that there are no gaps in between them. .. _sardana-countertimercontroller-per-measurement-preparation: Per measurement preparation ~~~~~~~~~~~~~~~~~~~~~~~~~~~ Since SEP18_ counter/timer controllers may take a profit from the per measurement preparation and reserve resources for a sequence of :attr:`~sardana.pool.pooldefs.AcqSynch.SoftwareTrigger` or :attr:`~sardana.pool.pooldefs.AcqSynch.SoftwareGate` acquisitions already in the :meth:`~sardana.pool.controller.Loadable.PrepareOne` method. This method is called only once at the beginning of the measurement e.g. :ref:`Deterministic step scans ` or :ref:`sardana-users-scan-continuous`. It enables an opportunity for significant dead time optimization thanks to the single per measurement configuration instead of the multiple per acquisition preparation using the :meth:`~sardana.pool.controller.Loadable.LoadOne`. Here is an example of the possible implementation of :meth:`~sardana.pool.controller.Loadable.PrepareOne`: .. code-block:: python :emphasize-lines: 3 class SpringfieldCounterTimerController(CounterTimerController): def PrepareOne(self, value, repetitions, latency, nb_starts): return self.springfield.SetNbStarts() .. _ALBA: http://www.cells.es/ .. _ANKA: http://http://ankaweb.fzk.de/ .. _ELETTRA: http://http://www.elettra.trieste.it/ .. _ESRF: http://www.esrf.eu/ .. _FRMII: http://www.frm2.tum.de/en/index.html .. _HASYLAB: http://hasylab.desy.de/ .. _MAX-lab: http://www.maxlab.lu.se/maxlab/max4/index.html .. _SOLEIL: http://www.synchrotron-soleil.fr/ .. _Tango: http://www.tango-controls.org/ .. _Taco: http://www.esrf.eu/Infrastructure/Computing/TACO/ .. _PyTango: http://packages.python.org/PyTango/ .. _Taurus: http://packages.python.org/taurus/ .. _QTango: http://www.tango-controls.org/download/index_html#qtango3 .. _Qt: http://qt.nokia.com/products/ .. _PyQt: http://www.riverbankcomputing.co.uk/software/pyqt/ .. _PyQwt: http://pyqwt.sourceforge.net/ .. _Python: http://www.python.org/ .. _IPython: http://ipython.org/ .. _ATK: http://www.tango-controls.org/Documents/gui/atk/tango-application-toolkit .. _Qub: http://www.blissgarden.org/projects/qub/ .. _numpy: http://numpy.scipy.org/ .. _SPEC: http://www.certif.com/ .. _EPICS: http://www.aps.anl.gov/epics/ .. _SEP18: http://www.sardana-controls.org/sep/?SEP18.md