How to write a counter/timer controller

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 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

import springfieldlib

from sardana.pool.controller import CounterTimerController

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 springfieldlib module which emulates a counter/timer hardware access library.

The springfieldlib can be downloaded from here.

The Springfield counter/timer controller can be downloaded from 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:

class SpringfieldBaseCounterTimerController(CounterTimerController):
    """The most basic controller intended from demonstration purposes only.
    This is the absolute minimum you have to implement to set a proper counter
    controller able to get a counter value, get a counter state and do an
    acquisition.
    
    This example is so basic that it is not even directly described in the
    documentation"""
    
    def __init__(self, inst, props, *args, **kwargs):
        """Constructor"""
        super(SpringfieldBaseCounterTimerController, self).__init__(inst, props, *args, **kwargs)
        self.springfield = springfieldlib.SpringfieldCounterHW()
        
    def ReadOne(self, axis):
        """Get the specified counter value"""
        return self.springfield.getValue(axis)
        
    def StateOne(self, axis):
        """Get the specified counter state"""
        springfield = self.springfield
        state = springfield.getState(axis)
        if state == 1:
            return State.On, "Counter is stopped"
        elif state == 2:
            return State.Moving, "Counter is acquiring"
        elif state == 3:
            return State.Fault, "Counter has an error"

    def StartAll(self):
        self.springfield.start_count()
            
    def StartOne(self, axis, value=None):
        """acquire the specified counter"""
        self.springfield.activate_channel(axis)              

    def LoadOne(self, axis, value):
        self.springfield.set_master(axis, value)
        
    def StopOne(self, axis):
        """Stop the specified counter"""
        self.springfield.stop(axis)        

This code is shown only to demonstrate the minimal controller API. The advanced counter/timer controller chapters describe how to account for more complex behaviour like reducing the number of hardware accesses.

Todo

finish counter/timer controller howto