[Question] HL DS synchronized with another DS

[hayg25]

Dear All,
I would like to create a DS (DS1) with 2 attributes (Att11, Att12).
This DS should be build from another existing DS (DS0) with 2 Attributes (Att01, Att02)
like : `

• Att11 = K1*Att01
• Att12 = K2*Att02
  K1 and K2 are some scaling factors in this case but the arithmetic operation for Att11, Att12, could be more complicated (polynomial, ... etc)
  I would like to do it for each event.

Do you have an example showing how to do this using PyTango.

Many thanks in advance

[andygotz]

@hayg25 this looks very close to what has been implemented in the Facade device at MaxIV. Vincent Michel, one of the authors, gave a great talk on this topic at ICALEPCS 2017: https://accelconf.web.cern.ch/icalepcs2017/talks/mobpl06_talk.pdf

There are links in there to the code. Hopefully someone from MaxIV can help you try it out.

Cheers

[vxgmichel]

this looks very close to what has been implemented in the Facade device at MaxIV.

Exactly! :)

Here's a link to the documentation:
https://tango-facadedevice.readthedocs.io/en/latest/

[hayg25]

Dear @andygotz, dear @vxgmichel ,
thanks a lot for the solution, that's exactly what I need.
I tried using a DS I created for testing :

from tango import DispLevel, AttrWriteType
from tango.server import run
from tango.server import Device, DeviceMeta
from tango.server import attribute, command
from tango import DevState
from numpy.random import random_sample


class DS_TEST(Device):
	__metaclass__ = DeviceMeta

# List of high level variables

	def init_device(self):
		Device.init_device(self)
		self._amplitude   = 0
		self._delay       = 0

		self.set_state(DevState.ON)

	amplitude  = attribute(label="Amplitude",   dtype=float,  access = AttrWriteType.READ_WRITE)
	delay      = attribute(label="Delay",       dtype=float,  access = AttrWriteType.READ_WRITE)

	def read_amplitude(self): 
		return self._amplitude			
	def write_amplitude(self,amplitude):
		self._amplitude = amplitude

	def read_delay(self):
		return self._delay
	def write_delay(self,delay):
		self._delay = delay


if __name__ == "__main__":
    run((DS_TEST,))

and I modified the example you gave :

from facadedevice import Facade, proxy_attribute, logical_attribute
from tango.server import run


class DS_REC(Facade):
    
    Width = proxy_attribute(
        dtype=float,
        property_name='WidthAttribute')
    
    Height = proxy_attribute(
        dtype=float,
        property_name='HeightAttribute')
    
    @logical_attribute(
        bind=['Width', 'Height'])
    def Sum(width, height):
        return width + height
    
if __name__ == '__main__':
    DS_REC.run_server()

so I set the properties for the new DS_REC.
And when I start the device,

1. It stays in Unknown state
2. none of the value is updated ...

Thanks

[AntoineDupre]

Hello @hayg25

It missing self in Sum arguments:

    @logical_attribute(
        bind=['Width', 'Height'])
    def Sum(self, width, height):
        return width + height

The two attributes Width and else Height are bind to the attribute defined in the properties:
WidthAttribute
WidthAttribute

This attribute can be set a tango attribute like domain/family/member/attribute (The tango attribute change/periodic event channel has to be enabled) or to a raw value.

The device state has to be managed manually (like a standard tango device). The state can also be bind to some facade attribute (https://tango-facadedevice.readthedocs.io/en/latest/tutorial.html#state-attribute)

You can always use the command GetInfo to get more details about the device.

[hayg25]

Hi @AntoineDupre ,
thanks for your help, indeed I missed the self argument !
It Works now. But still the DS status is in unknown mode : any idea ?

[ldoyle]

The device state and status are not changed to ON automatically, UNKNOWN will stay until you change it.
In normal Tango devices, I just use self.set_state() and self.set_status() in the appropriate places (e.g. at the end of init_device() or after some action failed inside a command). Remember to always update both (*) to keep them in sync.
I'm not familiar with this facadedevice, but the tutorial Antoine linked shows you how to do it easily with @state_attribute. Also, the section Adding extra logic at initialization shows how to add something similar to init_device() if you want to set the state there.

(*) If you only want to update state and keep status as the default "The device is in [STATE] state", you need to set_status to empty or 'Not initialised' I believe, since that is the default value and Tango will insert the right STATE always.

[AntoineDupre]

Hi @hayg25

As Idoyle mention, the state needs to be managed manually. It can be set in the safe_init_device function (function called after facade initialization):
More documentation there: https://tango-facadedevice.readthedocs.io/en/latest/tutorial.html#adding-extra-logic-at-initialization