Skip saving and log read-only PDO parameters.

For PDO communication or mapping parameters which are read-only on a
node, the PdoMap.save() method currently aborts with an SDO exception.
However, individual parameters may simply not support configuration
changes.  Rely on the Object Dictionary to tell which ones are
expected to fail and skip them.  For communication record entries, log
what is not being saved.

Author: erlend-aasland

canopen/pdo/base.py

@@ -15,7 +15,7 @@
 if TYPE_CHECKING:
     from canopen import LocalNode, RemoteNode
     from canopen.pdo import RPDO, TPDO
-    from canopen.sdo import SdoRecord
+    from canopen.sdo import SdoRecord, SdoVariable
 
 
 PDO_NOT_VALID = 1 << 31
@@ -404,18 +404,22 @@ def save(self) -> None:
             return
         logger.info("Setting COB-ID 0x%X and temporarily disabling PDO", self.cob_id)
         self.com_record[1].raw = self.cob_id | PDO_NOT_VALID | (RTR_NOT_ALLOWED if not self.rtr_allowed else 0x0)
-        if self.trans_type is not None:
-            logger.info("Setting transmission type to %d", self.trans_type)
-            self.com_record[2].raw = self.trans_type
-        if self.inhibit_time is not None:
-            logger.info("Setting inhibit time to %d us", (self.inhibit_time * 100))
-            self.com_record[3].raw = self.inhibit_time
-        if self.event_timer is not None:
-            logger.info("Setting event timer to %d ms", self.event_timer)
-            self.com_record[5].raw = self.event_timer
-        if self.sync_start_value is not None:
-            logger.info("Setting SYNC start value to %d", self.sync_start_value)
-            self.com_record[6].raw = self.sync_start_value
+
+        def _set_com_record(
+            subindex: int, value: Optional[int], log_fmt: str, log_factor: int = 1
+        ):
+            if value is None:
+                return
+            if self.com_record[subindex].writable:
+                logger.info(f"Setting {log_fmt}", value * log_factor)
+                self.com_record[subindex].raw = value
+            else:
+                logger.info(f"Cannot set {log_fmt}, not writable", value * log_factor)
+
+        _set_com_record(2, self.trans_type, "transmission type to %d")
+        _set_com_record(3, self.inhibit_time, "inhibit time to %d us", 100)
+        _set_com_record(5, self.event_timer, "event timer to %d ms")
+        _set_com_record(6, self.sync_start_value, "SYNC start value to %d")
 
         try:
             self.map_array[0].raw = 0
@@ -425,20 +429,16 @@ def save(self) -> None:
             # mappings for an invalid object 0x0000:00 to overwrite any
             # excess entries with all-zeros.
             self._fill_map(self.map_array[0].raw)
-        subindex = 1
-        for var in self.map:
+        for var, entry in zip(self.map, self.map_array):
+            if not entry.writable:
+                continue
             logger.info("Writing %s (0x%04X:%02X, %d bits) to PDO map",
                         var.name, var.index, var.subindex, var.length)
             if getattr(self.pdo_node.node, "curtis_hack", False):
                 # Curtis HACK: mixed up field order
-                self.map_array[subindex].raw = (var.index |
-                                                var.subindex << 16 |
-                                                var.length << 24)
+                entry.raw = var.index | var.subindex << 16 | var.length << 24
             else:
-                self.map_array[subindex].raw = (var.index << 16 |
-                                                var.subindex << 8 |
-                                                var.length)
-            subindex += 1
+                entry.raw = var.index << 16 | var.subindex << 8 | var.length
         try:
             self.map_array[0].raw = len(self.map)
         except SdoAbortedError as e: