frappy_psi.ah2700: create loss module automatically

using the Pinata mechanism

Change-Id: I07b06b2563241600fbe454366089717a59d55bdc

frappy_psi/ah2700.py

@@ -19,7 +19,9 @@
 # *****************************************************************************
 """Andeen Hagerling capacitance bridge"""
 
-from frappy.core import FloatRange, HasIO, Parameter, Readable, StringIO, nopoll
+from frappy.core import FloatRange, HasIO, Parameter, Readable, StringIO, nopoll, \
+    Attached, Property, StringType
+from frappy.dynamic import Pinata
 
 
 class Ah2700IO(StringIO):
@@ -27,14 +29,26 @@ class Ah2700IO(StringIO):
     timeout = 5
 
 
-class Capacitance(HasIO, Readable):
+class Capacitance(HasIO, Pinata, Readable):
 
     value = Parameter('capacitance', FloatRange(unit='pF'))
     freq = Parameter('frequency', FloatRange(unit='Hz'), readonly=False, default=0)
     voltage = Parameter('voltage', FloatRange(unit='V'), readonly=False, default=0)
-    loss = Parameter('loss', FloatRange(unit='deg'), default=0)
+    loss_name = Property('name of loss modules (default: <name>_loss)',
+                         StringType(), default='$_loss')
+    # loss = Parameter('loss', FloatRange(unit='deg'), default=0)
 
     ioClass = Ah2700IO
+    loss = 0
+
+    def scanModules(self):
+        if self.loss_name:
+            # if loss_name is not empty, we tell the framework to create
+            # a Loss module with this name, and config below
+            yield self.loss_name.replace('$', self.name), {
+                'cls': Loss,
+                'description': f'loss value of {self.name}',
+                'cap': self.name}
 
     def parse_reply(self, reply):
         if reply.startswith('SI'):  # this is an echo
@@ -72,11 +86,6 @@ class Capacitance(HasIO, Readable):
         self.read_value()
         return self.freq
 
-    @nopoll
-    def read_loss(self):
-        self.read_value()
-        return self.loss
-
     @nopoll
     def read_voltage(self):
         self.read_value()
@@ -89,3 +98,13 @@ class Capacitance(HasIO, Readable):
     def write_voltage(self, value):
         self.value = self.parse_reply(self.communicate(f'V {value:g};SI'))
         return self.voltage
+
+
+class Loss(Readable):
+    cap = Attached()
+    value = Parameter('loss', FloatRange(unit='deg'), default=0)
+
+    @nopoll
+    def read_value(self):
+        self.cap.read_value()
+        return self.cap.loss