diff --git a/Tools/ardupilotwaf/chibios.py b/Tools/ardupilotwaf/chibios.py
index 785bce15bcee5..ea0ebab4477e0 100644
--- a/Tools/ardupilotwaf/chibios.py
+++ b/Tools/ardupilotwaf/chibios.py
@@ -16,6 +16,10 @@
 import base64
 import subprocess
 
+# modify our search path:
+sys.path.append(os.path.join(os.path.dirname(os.path.realpath(__file__)), '../../libraries/AP_HAL_ChibiOS/hwdef/scripts'))
+import chibios_hwdef
+
 _dynamic_env_data = {}
 def _load_dynamic_env_data(bld):
     bldnode = bld.bldnode.make_node('modules/ChibiOS')
@@ -638,17 +642,27 @@ def generate_hwdef_h(env):
         print(env.BOOTLOADER_OPTION)
         env.BOOTLOADER_OPTION += " --signed-fw"
         print(env.BOOTLOADER_OPTION)
-    hwdef_script = os.path.join(env.SRCROOT, 'libraries/AP_HAL_ChibiOS/hwdef/scripts/chibios_hwdef.py')
     hwdef_out = env.BUILDROOT
     if not os.path.exists(hwdef_out):
         os.mkdir(hwdef_out)
-    python = sys.executable
-    cmd = "{0} '{1}' -D '{2}' --params '{3}' '{4}'".format(python, hwdef_script, hwdef_out, env.DEFAULT_PARAMETERS, env.HWDEF)
+
+    # Build a list of the hardware definitions
+    hwdef_arr = [env.HWDEF]
     if env.HWDEF_EXTRA:
-        cmd += " '{0}'".format(env.HWDEF_EXTRA)
-    if env.BOOTLOADER_OPTION:
-        cmd += " " + env.BOOTLOADER_OPTION
-    return subprocess.call(cmd, shell=True)
+        # Add any extra hwdefs that may be defined
+        hwdef_arr.append(env.HWDEF_EXTRA)
+    ch = chibios_hwdef.ChibiOSHWDef(outdir=hwdef_out,
+                                    bootloader=env.BOOTLOADER,
+                                    signed_fw=env.AP_SIGNED_FIRMWARE,
+                                    default_params_filepath=env.DEFAULT_PARAMETERS,
+                                    hwdef=hwdef_arr)
+    try:
+        ch.run()
+        # Return success for subprocess call
+        return 0
+    except SystemExit:
+        # The run failed, so return the error code
+        return 1
 
 def pre_build(bld):
     '''pre-build hook to change dynamic sources'''
@@ -668,21 +682,18 @@ def pre_build(bld):
 
 def build(bld):
 
-
-    hwdef_rule="%s '%s/hwdef/scripts/chibios_hwdef.py' -D '%s' --params '%s' '%s'" % (
-            bld.env.get_flat('PYTHON'),
-            bld.env.AP_HAL_ROOT,
-            bld.env.BUILDROOT,
-            bld.env.default_parameters,
-            bld.env.HWDEF)
+    hwdef_arr = [bld.env.HWDEF]
     if bld.env.HWDEF_EXTRA:
-        hwdef_rule += " " + bld.env.HWDEF_EXTRA
-    if bld.env.BOOTLOADER_OPTION:
-        hwdef_rule += " " + bld.env.BOOTLOADER_OPTION
+        hwdef_arr.append(bld.env.HWDEF_EXTRA)
+    ch = chibios_hwdef.ChibiOSHWDef(outdir=bld.env.BUILDROOT,
+                                    bootloader=bld.env.BOOTLOADER,
+                                    signed_fw=bld.env.AP_SIGNED_FIRMWARE,
+                                    default_params_filepath=bld.env.DEFAULT_PARAMETERS,
+                                    hwdef=hwdef_arr)
     bld(
         # build hwdef.h from hwdef.dat. This is needed after a waf clean
         source=bld.path.ant_glob(bld.env.HWDEF),
-        rule=hwdef_rule,
+        rule=ch.run,
         group='dynamic_sources',
         target=[bld.bldnode.find_or_declare('hwdef.h'),
                 bld.bldnode.find_or_declare('ldscript.ld'),
diff --git a/libraries/AP_HAL_ChibiOS/hwdef/scripts/chibios_hwdef.py b/libraries/AP_HAL_ChibiOS/hwdef/scripts/chibios_hwdef.py
index 935db8536f8bb..2dcb411e85d45 100644
--- a/libraries/AP_HAL_ChibiOS/hwdef/scripts/chibios_hwdef.py
+++ b/libraries/AP_HAL_ChibiOS/hwdef/scripts/chibios_hwdef.py
@@ -2891,12 +2891,14 @@ def get_processed_defaults_file(self, defaults_filepath, depth=0):
     def write_processed_defaults_file(self, filepath):
         # see if board has a defaults.parm file or a --default-parameters file was specified
         defaults_filename = os.path.join(os.path.dirname(self.hwdef[0]), 'defaults.parm')
-        defaults_path = os.path.join(os.path.dirname(self.hwdef[0]), args.params)
-
         defaults_abspath = None
-        if os.path.exists(defaults_path):
-            defaults_abspath = os.path.abspath(self.default_params_filepath)
-            self.progress("Default parameters path from command line: %s" % self.default_params_filepath)
+        if isinstance(self.default_params_filepath, str):
+            defaults_path = os.path.join(os.path.dirname(self.hwdef[0]), self.default_params_filepath)
+            if not os.path.exists(defaults_path):
+                self.error(f"Specified defaults file not found at path {defaults_path}")
+
+            defaults_abspath = os.path.abspath(defaults_path)
+            self.progress("Default parameters path from command line: %s" % defaults_path)
         elif os.path.exists(defaults_filename):
             defaults_abspath = os.path.abspath(defaults_filename)
             self.progress("Default parameters path from hwdef: %s" % defaults_filename)
diff --git a/wscript b/wscript
index f400c74cdb7ee..18ef844f6d8a2 100644
--- a/wscript
+++ b/wscript
@@ -491,8 +491,8 @@ def configure(cfg):
     _set_build_context_variant(cfg.env.BOARD)
     cfg.setenv(cfg.env.BOARD)
 
+    cfg.env.AP_SIGNED_FIRMWARE = cfg.options.signed_fw
     if cfg.options.signed_fw:
-        cfg.env.AP_SIGNED_FIRMWARE = True
         cfg.options.enable_check_firmware = True
 
     cfg.env.BOARD = cfg.options.board