PDO: Allow subscription without calling read() or save()

canopen/pdo/__init__.py

@@ -8,7 +8,8 @@
 
 
 class PDO(PdoBase):
-    """PDO Class for backwards compatibility
+    """PDO Class for backwards compatibility.
+
     :param rpdo: RPDO object holding the Receive PDO mappings
     :param tpdo: TPDO object holding the Transmit PDO mappings
     """
@@ -27,9 +28,11 @@ def __init__(self, node, rpdo, tpdo):
 
 
 class RPDO(PdoBase):
-    """PDO specialization for the Receive PDO enabling the transfer of data from the master to the node.
+    """Receive PDO to transfer data from somewhere to the represented node.
+
     Properties 0x1400 to 0x1403 | Mapping 0x1600 to 0x1603.
-    :param object node: Parent node for this object."""
+    :param object node: Parent node for this object.
+    """
 
     def __init__(self, node):
         super(RPDO, self).__init__(node)
@@ -38,8 +41,10 @@ def __init__(self, node):
 
     def stop(self):
         """Stop transmission of all RPDOs.
+
         :raise TypeError: Exception is thrown if the node associated with the PDO does not
-        support this function"""
+        support this function.
+        """
         if isinstance(self.node, canopen.RemoteNode):
             for pdo in self.map.values():
                 pdo.stop()
@@ -48,8 +53,11 @@ def stop(self):
 
 
 class TPDO(PdoBase):
-    """PDO specialization for the Transmit PDO enabling the transfer of data from the node to the master.
-    Properties 0x1800 to 0x1803 | Mapping 0x1A00 to 0x1A03."""
+    """Transmit PDO to broadcast data from the represented node to the network.
+
+    Properties 0x1800 to 0x1803 | Mapping 0x1A00 to 0x1A03.
+    :param object node: Parent node for this object.
+    """
 
     def __init__(self, node):
         super(TPDO, self).__init__(node)
@@ -58,8 +66,10 @@ def __init__(self, node):
 
     def stop(self):
         """Stop transmission of all TPDOs.
+
         :raise TypeError: Exception is thrown if the node associated with the PDO does not
-        support this function"""
+        support this function.
+        """
         if isinstance(canopen.LocalNode, self.node):
             for pdo in self.map.values():
                 pdo.stop()

canopen/pdo/base.py

@@ -59,6 +59,17 @@ def save(self):
         for pdo_map in self.map.values():
             pdo_map.save()
 
+    def subscribe(self):
+        """Register the node's PDOs for reception on the network.
+
+        This normally happens when the PDO configuration is read from
+        or saved to the node.  Use this method to avoid the SDO flood
+        associated with read() or save(), if the local PDO setup is
+        known to match what's stored on the node.
+        """
+        for pdo_map in self.map.values():
+            pdo_map.subscribe()
+
     def export(self, filename):
         """Export current configuration to a database file.
 
@@ -331,8 +342,7 @@ def read(self):
             if index and size:
                 self.add_variable(index, subindex, size)
 
-        if self.enabled:
-            self.pdo_node.network.subscribe(self.cob_id, self.on_message)
+        self.subscribe()
 
     def save(self):
         """Save PDO configuration for this map using SDO."""
@@ -387,9 +397,19 @@ def save(self):
             self._update_data_size()
 
         if self.enabled:
-            logger.info("Enabling PDO")
             self.com_record[1].raw = self.cob_id | (RTR_NOT_ALLOWED if not self.rtr_allowed else 0x0)
+            self.subscribe()
+
+    def subscribe(self):
+        """Register the PDO for reception on the network.
 
+        This normally happens when the PDO configuration is read from
+        or saved to the node.  Use this method to avoid the SDO flood
+        associated with read() or save(), if the local PDO setup is
+        known to match what's stored on the node.
+        """
+        if self.enabled:
+            logger.info("Subscribing to enabled PDO 0x%X on the network", self.cob_id)
             self.pdo_node.network.subscribe(self.cob_id, self.on_message)
 
     def clear(self):