sardana.macroserver.macro
In general terms, we call scan to a macro that moves one or more motors and acquires data along the path of the motor(s). See the introduction to the concept of scan in Sardana <sardana-users-scan>
.
While a scan macro could be written from scratch, Sardana provides a higher-level API (the scan framework) that greatly simplifies the development of scan macros by taking care of the details about synchronization of motors and of acquisitions.
The scan framework is implemented in the ~sardana.macroserver.scan
module, which provides the ~sardana.macroserver.scan.GScan
base class and its specialized derived classes ~sardana.macroserver.scan.SScan
and ~sardana.macroserver.scan.CScan
for step and continuous scans, respectively.
Creating a scan macro consists in writing a generic macro (see the generic macro writing instructions <sardana-macros-howto>
) in which an instance of ~sardana.macroserver.scan.GScan
is created (typically in the ~Macro.prepare
method) which is then invoked in the ~Macro.run
method.
Central to the scan framework is the ~sardana.macroserver.macro.scan.gscan.GScan.generator
function, which must be passed to the GScan constructor. This generator is a function that allows to construct the path of the scan (see ~sardana.macroserver.scan.GScan
for detailed information on the generator).
Step scans are built using an instance of the ~sardana.macroserver.scan.SScan
class, which requires a step generator that defines the path for the motion. Since in a step scan the data is acquired at each step, the generator controls both the motion and the acquisition.
Note that in general, the generator does not need to generate a determinate (or even finite) number of steps. Also note that it is possible to write generators that vary their current step based on the acquired values (e.g., changing step sizes as a function of some counter reading).
The ~sardana.macroserver.macros.examples.ascan_demo
macro illustrates the most basic features of a step scan:
class ascan_demo(Macro):
"""
This is a basic reimplementation of the ascan` macro for demonstration
purposes of the Generic Scan framework. The "real" implementation of
:class:`sardana.macroserver.macros.ascan` derives from
:class:`sardana.macroserver.macros.aNscan` and provides some extra features.
"""
hints = { 'scan' : 'ascan_demo'} #this is used to indicate other codes that the macro is a scan
env = ('ActiveMntGrp',) #this hints that the macro requires the ActiveMntGrp environment variable to be set
param_def = [
['motor', Type.Moveable, None, 'Motor to move'],
['start_pos', Type.Float, None, 'Scan start position'],
['final_pos', Type.Float, None, 'Scan final position'],
['nr_interv', Type.Integer, None, 'Number of scan intervals'],
['integ_time', Type.Float, None, 'Integration time']
]
def prepare(self, motor, start_pos, final_pos, nr_interv, integ_time, **opts):
#parse the user parameters
self.start = numpy.array([start_pos], dtype='d')
self.final = numpy.array([final_pos], dtype='d')
self.integ_time = integ_time
self.nr_points = nr_interv+1
self.interv_size = ( self.final - self.start) / nr_interv
self.name='ascan_demo'
env = opts.get('env',{}) #the "env" dictionary may be passed as an option
#create an instance of GScan (in this case, of its child, SScan
self._gScan=SScan(self, generator=self._generator, moveables=[motor], env=env)
def _generator(self):
step = {}
step["integ_time"] = self.integ_time #integ_time is the same for all steps
for point_no in xrange(self.nr_points):
step["positions"] = self.start + point_no * self.interv_size #note that this is a numpy array
step["point_id"] = point_no
yield step
def run(self,*args):
for step in self._gScan.step_scan(): #just go through the steps
yield step
@property
def data(self):
return self._gScan.data #the GScan provides scan data
The ~sardana.macroserver.macros.examples.ascan_demo
shows only basic features of the scan framework, but it already shows that writing a step scan macro is mostly just a matter of writing a generator function.
It also shows that the scan.gscan.GScan.data
method can be used to provide the needed return value of ~Macro.data
Continuous scans are built using an instance of the ~sardana.macroserver.scan.CScan
class. Since in the continuous scans the acquisition and motion are decoupled, CScan requires two independent generators:
- a waypoint generator: which defines the path for the motion in a very similar way as the step generator does for a continuous scan. The steps generated by this generator are also called "waypoints".
- a period generator which controls the data acquisition steps.
Essentially, ~sardana.macroserver.scan.CScan
implements the continuous scan as an acquisition loop (controlled by the period generator) nested within a motion loop (controlled by the waypoint generator). Note that each loop is run on an independent thread, and only limited communication occurs between the two (basically the acquisition starts at the beginning of each movement and ends when a waypoint is reached).
The ~sardana.macroserver.macros.examples.ascanc_demo
macro illustrates the most basic features of a continuous scan:: :
class ascanc_demo(Macro):
"""
This is a basic reimplementation of the ascanc` macro for demonstration
purposes of the Generic Scan framework. The "real" implementation of
:class:`sardana.macroserver.macros.ascanc` derives from
:class:`sardana.macroserver.macros.aNscan` and provides some extra features.
"""
hints = { 'scan' : 'ascanc_demo'} #this is used to indicate other codes that the macro is a scan
env = ('ActiveMntGrp',) #this hints that the macro requires the ActiveMntGrp environment variable to be set
param_def = [
['motor', Type.Moveable, None, 'Motor to move'],
['start_pos', Type.Float, None, 'Scan start position'],
['final_pos', Type.Float, None, 'Scan final position'],
['integ_time', Type.Float, None, 'Integration time']
]
def prepare(self, motor, start_pos, final_pos, integ_time, **opts):
self.name='ascanc_demo'
#parse the user parameters
self.start = numpy.array([start_pos], dtype='d')
self.final = numpy.array([final_pos], dtype='d')
self.integ_time = integ_time
env = opts.get('env',{}) #the "env" dictionary may be passed as an option
#create an instance of GScan (in this case, of its child, CScan
self._gScan = CScan(self,
waypointGenerator=self._waypoint_generator,
periodGenerator=self._period_generator,
moveables=[motor],
env=env)
def _waypoint_generator(self):
#a very simple waypoint generator! only start and stop points!
yield {"positions":self.start, "waypoint_id": 0}
yield {"positions":self.final, "waypoint_id": 1}
def _period_generator(self):
step = {}
step["integ_time"] = self.integ_time
point_no = 0
while(True): #infinite generator. The acquisition loop is started/stopped at begin and end of each waypoint
point_no += 1
step["point_id"] = point_no
yield step
def run(self,*args):
for step in self._gScan.step_scan():
yield step
for another example of a continuous scan implementation (with more elaborated waypoint generator), see the code of ~sardana.macroserver.macros.scan.meshc
In general, the Hooks API provided by the ~sardana.macroserver.macro.Hookable
base class allows a macro to run other code (the hook callable) at certain points of its execution. The hooks use a "hints" mechanism to pass the receiving macro some extra information on how/when they should be executed. The hints are strings, and its content is not fixed by the API, being up to each macro to identify, use and/or ignore them.
You can find some examples of the use of hooks in the ~sardana.macroserver.macros.examples.hooks
module.
In the case of the scan macros, the hooks can be either registered directly via the Hooks API or passed as key:values of the "step" dictionary returned by the scan ~sardana.macroserver.macro.scan.gscan.GScan.generator
(see ~sardana.macroserver.macro.scan.gscan.GScan
for more details).
The hints for a given hook are used by the scan framework to select the moment of the scan execution that the given hook is run. The following is a list of hint strings that scan macros support (other hints are ignored):
- 'pre-scan-hooks' : before starting the scan.
- 'pre-move-hooks' : for steps: before starting to move.
- 'post-move-hooks': for steps: after finishing the move.
- 'pre-acq-hooks' : for steps: before starting to acquire.
- 'post-acq-hooks' : for steps: after finishing acquisition but before recording the step.
- 'post-step-hooks' : for steps: after finishing recording the step.
- 'post-scan-hooks' : after finishing the scan
See the code of ~sardana.macroserver.macros.examples.hooks.hooked_scan
for a macro that demonstrates the use of the hook points of a scan.
Other examples of the ~sardana.macroserver.macros.examples.hooks
module can be illustrative.
Also, note that the Taurus MacroExecutor widget allows the user to dynamically add hooks to existing macros before execution.
Other macros in the ~sardana.macroserver.macros.examples
module illustrate more features of the scan framework.
See also the code of the standard scan macros in the ~sardana.macroserver.macros.scan
module.
Finally, the documentation and code of ~sardana.macroserver.scan.GScan
, ~sardana.macroserver.scan.SScan
and ~sardana.macroserver.scan.CScan
may be helpful.