diff --git a/py/mkrules.mk b/py/mkrules.mk
index 5050935873..4addac38a6 100644
--- a/py/mkrules.mk
+++ b/py/mkrules.mk
@@ -206,6 +206,9 @@ MICROPY_MANIFEST_MPY_LIB_DIR = $(MPY_LIB_DIR)
 MICROPY_MANIFEST_PORT_DIR = $(shell pwd)
 MICROPY_MANIFEST_BOARD_DIR = $(BOARD_DIR)
 MICROPY_MANIFEST_MPY_DIR = $(TOP)
+# Set variables for BOARD and BOARD_VARIANT by default
+MICROPY_MANIFEST_BOARD = $(BOARD)
+MICROPY_MANIFEST_BOARD_VARIANT = $(BOARD_VARIANT)
 
 # Find all MICROPY_MANIFEST_* variables and turn them into command line arguments.
 MANIFEST_VARIABLES = $(foreach var,$(filter MICROPY_MANIFEST_%, $(.VARIABLES)),-v "$(subst MICROPY_MANIFEST_,,$(var))=$($(var))")
diff --git a/tools/makemanifest.py b/tools/makemanifest.py
index a74a6934ae..92b9cfaf92 100644
--- a/tools/makemanifest.py
+++ b/tools/makemanifest.py
@@ -143,7 +143,7 @@ def main():
     # Extract variables for substitution.
     for var in args.var:
         name, value = var.split("=", 1)
-        if os.path.exists(value):
+        if name in ("MPY_DIR", "MPY_LIB_DIR", "BOARD_DIR", "PORT_DIR") and os.path.exists(value):
             value = os.path.abspath(value)
         VARS[name] = value
 
diff --git a/tools/manifestfile.py b/tools/manifestfile.py
index beaa36d0f5..c0efb4d662 100644
--- a/tools/manifestfile.py
+++ b/tools/manifestfile.py
@@ -222,6 +222,7 @@ class ManifestFile:
             "add_library": self.add_library,
             "package": self.package,
             "module": self.module,
+            "resolve": self.resolve,
             "options": IncludeOptions(**kwargs),
         }
 
@@ -572,6 +573,12 @@ class ManifestFile:
         """
         self._freeze_internal(path, script, exts=(".mpy",), kind=KIND_FREEZE_MPY, opt=opt)
 
+    def resolve(self, name):
+        if name[0] == "$" and name[1:] in self._path_vars.keys():
+            return self._path_vars[name[1:]]
+        else:
+            return None
+
 
 # Generate a temporary file with a line appended to the end that adds __version__.
 @contextlib.contextmanager