configs,ext,stdlib: Update DRAMSys integration (#525)

Recent breaking changes in the DRAMSys API require user code to be
updated. These updates have been applied to the gem5 integration.

Furthermore, as DRAMSys started to use CMake dependency management,
it is no longer sensible to maintain two separate build systems for
DRAMSys. The use of the DRAMSys integration in gem5 will therefore
from now on require that CMake is installed on the target machine.

Additionally, support for snapshots have been implemented into DRAMSys
and coupled with gem5's checkpointing API.

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

@@ -24,7 +24,8 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-import m5
+from typing import Tuple, Sequence, List, Optional
+from pathlib import Path
 
 from m5.objects import (
     DRAMSys,
@@ -40,27 +41,46 @@ from ...utils.override import overrides
 from ..boards.abstract_board import AbstractBoard
 from .abstract_memory_system import AbstractMemorySystem
 
-from typing import Tuple, Sequence, List
+
+DEFAULT_DRAMSYS_DIRECTORY = Path("ext/dramsys/DRAMSys")
 
 
 class DRAMSysMem(AbstractMemorySystem):
+    """
+    A DRAMSys memory controller.
+
+    This class requires gem5 to be built with DRAMSys (see ext/dramsys).
+    The specified memory size does not control the simulated memory size but it's sole purpose is
+    to notify gem5 of DRAMSys's memory size.
+    Therefore it has to match the DRAMSys configuration.
+    DRAMSys is configured using JSON files, whose base configuration has to be passed as a
+    parameter. Sub-configs are specified relative to the optional resource directory parameter.
+    """
+
     def __init__(
         self,
         configuration: str,
         size: str,
-        resource_directory: str,
         recordable: bool,
+        resource_directory: Optional[str] = None,
     ) -> None:
         """
         :param configuration: Path to the base configuration JSON for DRAMSys.
         :param size: Memory size of DRAMSys. Must match the size specified in JSON configuration.
-        :param resource_directory: Path to the base resource directory for DRAMSys.
         :param recordable: Whether the database recording feature of DRAMSys is enabled.
+        :param resource_directory: Path to the base resource directory for DRAMSys.
         """
         super().__init__()
+
+        resource_directory_path = (
+            DEFAULT_DRAMSYS_DIRECTORY / "configs"
+            if resource_directory is None
+            else Path(resource_directory)
+        )
+
         self.dramsys = DRAMSys(
             configuration=configuration,
-            resource_directory=resource_directory,
+            resource_directory=resource_directory_path.as_posix(),
             recordable=recordable,
         )
 
@@ -97,56 +117,72 @@ class DRAMSysMem(AbstractMemorySystem):
 
 
 class DRAMSysDDR4_1866(DRAMSysMem):
+    """
+    An example DDR4 1866 DRAMSys configuration.
+    """
+
     def __init__(self, recordable: bool):
         """
         :param recordable: Whether the database recording feature of DRAMSys is enabled.
         """
         super().__init__(
-            configuration="ext/dramsys/DRAMSys/DRAMSys/"
-            "library/resources/simulations/ddr4-example.json",
+            configuration=(
+                DEFAULT_DRAMSYS_DIRECTORY / "configs/ddr4-example.json"
+            ).as_posix(),
             size="4GB",
-            resource_directory="ext/dramsys/DRAMSys/DRAMSys/library/resources",
             recordable=recordable,
         )
 
 
 class DRAMSysDDR3_1600(DRAMSysMem):
+    """
+    An example DDR3 1600 DRAMSys configuration.
+    """
+
     def __init__(self, recordable: bool):
         """
         :param recordable: Whether the database recording feature of DRAMSys is enabled.
         """
         super().__init__(
-            configuration="ext/dramsys/DRAMSys/DRAMSys/"
-            "library/resources/simulations/ddr3-gem5-se.json",
-            size="4GB",
-            resource_directory="ext/dramsys/DRAMSys/DRAMSys/library/resources",
+            configuration=(
+                DEFAULT_DRAMSYS_DIRECTORY / "configs/ddr3-gem5-se.json"
+            ).as_posix(),
+            size="1GB",
             recordable=recordable,
         )
 
 
 class DRAMSysLPDDR4_3200(DRAMSysMem):
+    """
+    An example LPDDR4 3200 DRAMSys configuration.
+    """
+
     def __init__(self, recordable: bool):
         """
         :param recordable: Whether the database recording feature of DRAMSys is enabled.
         """
         super().__init__(
-            configuration="ext/dramsys/DRAMSys/DRAMSys/"
-            "library/resources/simulations/lpddr4-example.json",
-            size="4GB",
-            resource_directory="ext/dramsys/DRAMSys/DRAMSys/library/resources",
+            configuration=(
+                DEFAULT_DRAMSYS_DIRECTORY / "configs/lpddr4-example.json"
+            ).as_posix(),
+            size="1GB",
             recordable=recordable,
         )
 
 
 class DRAMSysHBM2(DRAMSysMem):
+    """
+    An example HBM2 DRAMSys configuration.
+    """
+
     def __init__(self, recordable: bool):
         """
         :param recordable: Whether the database recording feature of DRAMSys is enabled.
         """
         super().__init__(
-            configuration="ext/dramsys/DRAMSys/DRAMSys/"
-            "library/resources/simulations/hbm2-example.json",
-            size="4GB",
-            resource_directory="ext/dramsys/DRAMSys/DRAMSys/library/resources",
+            configuration=(
+                DEFAULT_DRAMSYS_DIRECTORY / "configs/hbm2-example.json"
+            ).as_posix(),
+            size="1GB",
             recordable=recordable,
         )