DAP: clean up and correct access of the session.

- DebugPort uses the target's session for subscribing to reset events,
  since there might not be a probe in certain cases.
- DAPConnector asserts that it has a valid session.
- AccessPort consistently gets the session from the DP.

Author: flit

pyocd/coresight/ap.py

@@ -522,7 +522,7 @@ def __init__(self, dp, ap_address, idr=None, name="", flags=0, cmpid=None):
             self.read_memory_block32 = self._read_memory_block32
 
         # Subscribe to reset events.
-        self.dp.probe.session.subscribe(self._reset_did_occur, (Target.Event.PRE_RESET, Target.Event.POST_RESET))
+        self.dp.session.subscribe(self._reset_did_occur, (Target.Event.PRE_RESET, Target.Event.POST_RESET))
 
     @property
     def supported_transfer_sizes(self):
@@ -707,7 +707,7 @@ def find_components(self):
                     self.rom_table.init()
         except exceptions.TransferError as error:
             LOG.error("Transfer error while reading %s ROM table: %s", self.short_description, error,
-                exc_info=self.dp.target.session.log_tracebacks)
+                exc_info=self.dp.session.log_tracebacks)
 
     @property
     def implemented_hprot_mask(self):

pyocd/coresight/dap.py

@@ -116,6 +116,10 @@ def __init__(self, probe):
         self._probe = probe
         self._session = probe.session
         self._idr = None
+        
+        # Make sure we have a session, since we get the session from the probe and probes have their session set
+        # after creation.
+        assert self._session is not None, "DPConnector requires the probe to have a session"
 
     @property
     def idr(self):
@@ -225,7 +229,7 @@ def __init__(self, probe, target):
         self._apacc_mem_interface = None
 
         # Subscribe to reset events.
-        self._probe.session.subscribe(self._reset_did_occur, (Target.Event.PRE_RESET, Target.Event.POST_RESET))
+        self._session.subscribe(self._reset_did_occur, (Target.Event.PRE_RESET, Target.Event.POST_RESET))
 
     @property
     def probe(self):