stdlib: Add _post_instantiate function

This function will be called on the board after m5.instantiate is
called. This is useful, for instance, to start traffic generators.
Currently all implementations simply `pass`.

Change-Id: Ie2ab3fdddca5f3978d98191e5c08504561587fbb
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/64016
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>

src/python/gem5/components/boards/abstract_board.py

@@ -338,3 +338,10 @@ class AbstractBoard:
 
         # Incorporate the processor into the motherboard.
         self.get_processor().incorporate_processor(self)
+
+    def _post_instantiate(self):
+        """Called to set up anything needed after m5.instantiate"""
+        self.get_processor()._post_instantiate()
+        if self.get_cache_hierarchy():
+            self.get_cache_hierarchy()._post_instantiate()
+        self.get_memory()._post_instantiate()

src/python/gem5/components/cachehierarchies/abstract_cache_hierarchy.py

@@ -70,3 +70,7 @@ class AbstractCacheHierarchy(SubSystem):
         :returns: True if the cache hierarchy is ruby. Otherwise False.
         """
         raise NotImplementedError
+
+    def _post_instantiate(self):
+        """Called to set up anything needed after m5.instantiate"""
+        pass

src/python/gem5/components/memory/abstract_memory_system.py

@@ -71,3 +71,7 @@ class AbstractMemorySystem(SubSystem):
         will be raised.
         """
         raise NotImplementedError
+
+    def _post_instantiate(self) -> None:
+        """Called to set up anything needed after m5.instantiate"""
+        pass

src/python/gem5/components/processors/abstract_processor.py

@@ -74,3 +74,7 @@ class AbstractProcessor(SubSystem):
     @abstractmethod
     def incorporate_processor(self, board: AbstractBoard) -> None:
         raise NotImplementedError
+
+    def _post_instantiate(self) -> None:
+        """Called to set up anything needed after m5.instantiate"""
+        pass

src/python/gem5/simulate/simulator.py

@@ -405,6 +405,10 @@ class Simulator:
             m5.instantiate(self._checkpoint_path)
             self._instantiated = True
 
+            # Let the board know that instantiate has been called so it can do
+            # any final things.
+            self._board._post_instantiate()
+
     def run(self, max_ticks: int = m5.MaxTick) -> None:
         """
         This function will start or continue the simulator run and handle exit