WIP: deciding on certain features in backend conversion

src/ophyd_async/core/_soft_signal_backend.py

@@ -128,11 +128,6 @@ def make_initial_value(self, datatype: Optional[Type[T]]) -> T:
 
 
 class SoftProtocolDatatypeAbstractionConverter(SoftConverter):
-    """
-    No conversion is necessary for ProtocolDatatypeAbstraction datatypes in soft
-    signals.
-    """
-
     def __init__(self, datatype: Type[ProtocolDatatypeAbstraction]):
         self.datatype = datatype
 
@@ -141,7 +136,8 @@ def reading(self, value: T, timestamp: float, severity: int) -> Reading:
         return super().reading(value, timestamp, severity)
 
     def value(self, value: Any) -> Any:
-        if not issubclass(type(value), ProtocolDatatypeAbstraction):
+        if not isinstance(value, self.datatype):
+            # For the case where we 
             value = self.datatype.convert_from_protocol_datatype(value)
         return value
 
@@ -197,7 +193,6 @@ def __init__(
         self.datatype = datatype
         self._initial_value = initial_value
         self._metadata = metadata or {}
-        self.converter_factory = SoftSignalConverterFactory
         self.converter: SoftConverter = SoftSignalConverterFactory.make_converter(
             datatype
         )

src/ophyd_async/epics/signal/_p4p.py

@@ -312,7 +312,9 @@ def value(self, value: Value):
         return self.datatype.convert_from_protocol_datatype(value.todict())
 
     def write_value(self, value):
-        return value.convert_to_protocol_datatype()
+        if isinstance(value, self.datatype):
+            return value.convert_to_protocol_datatype()
+        return value
 
 
 class PvaConverterFactory(BackendConverterFactory):
@@ -428,7 +430,6 @@ def __init__(self, datatype: Optional[Type[T]], read_pv: str, write_pv: str):
         self.read_pv = read_pv
         self.write_pv = write_pv
         self.initial_values: Dict[str, Any] = {}
-        self.converter_factory = PvaConverterFactory()
         self.converter: PvaConverter = DisconnectedPvaConverter()
         self.subscription: Optional[Subscription] = None
 

tests/core/test_device_save_loader.py

@@ -22,6 +22,7 @@
     set_signal_values,
     walk_rw_signals,
 )
+from ophyd_async.core._signal_backend import ProtocolDatatypeAbstraction
 from ophyd_async.epics.signal import epics_signal_r, epics_signal_rw
 
 
@@ -54,6 +55,18 @@ class MyEnum(str, Enum):
     three = "three"
 
 
+class SomeProtocolDatatypeAbstraction(ProtocolDatatypeAbstraction):
+    def __init__(self, value: int):
+        self.value = value
+
+    def convert_to_protocol_datatype(self) -> int:    
+        return self.value - 1
+
+    @classmethod
+    def convert_from_protocol_datatype(cls, value: int) -> "SomeProtocolDatatypeAbstraction":
+        return cls(value + 1)
+
+
 class DummyDeviceGroupAllTypes(Device):
     def __init__(self, name: str):
         self.pv_int: SignalRW = epics_signal_rw(int, "PV1")
@@ -73,6 +86,7 @@ def __init__(self, name: str):
         self.pv_array_float64 = epics_signal_rw(npt.NDArray[np.float64], "PV14")
         self.pv_array_npstr = epics_signal_rw(npt.NDArray[np.str_], "PV15")
         self.pv_array_str = epics_signal_rw(Sequence[str], "PV16")
+        self.pv_protocol_device_abstraction = epics_signal_rw(SomeProtocolDatatypeAbstraction, "PV17")
 
 
 @pytest.fixture
@@ -155,6 +169,9 @@ async def test_save_device_all_types(RE: RunEngine, device_all_types, tmp_path):
     await device_all_types.pv_array_str.set(
         ["one", "two", "three"],
     )
+    await device_all_types.pv_protocol_device_abstraction.set(
+        SomeProtocolDatatypeAbstraction(1)
+    )
 
     # Create save plan from utility functions
     def save_my_device():

tests/test_data/test_yaml_save.yml

@@ -20,3 +20,4 @@
   pv_float: 1.234
   pv_int: 1
   pv_str: test_string
+  pv_protocol_device_abstraction: 0