Allow flashing only the kernel without any app.

deploy.py

@@ -485,6 +485,7 @@ class OpenSKInstaller:
         kern_hex.frombytes(kernel.read(), offset=board_props.kernel_address)
         final_hex.merge(kern_hex, overlap="error")
 
+    if self.args.application:
       # Add padding
       if board_props.padding_address:
         padding_hex = intelhex.IntelHex()
@@ -546,9 +547,6 @@ class OpenSKInstaller:
     self.check_prerequisites()
     self.update_rustc_if_needed()
 
-    if self.args.application is None:
-      fatal("Please specify an application to be flashed")
-
     # Compile what needs to be compiled
     if self.args.tockos:
       self.build_tockos()
@@ -556,6 +554,8 @@ class OpenSKInstaller:
     if self.args.application == "ctap2":
       self.generate_crypto_materials(self.args.regenerate_keys)
       self.build_opensk()
+    elif self.args.application is None:
+      info("No application selected.")
     else:
       self.build_example()
 
@@ -568,16 +568,19 @@ class OpenSKInstaller:
       if self.args.tockos:
         # Install Tock OS
         self.install_tock_os()
-      # Install padding and application
+      # Install padding and application if needed
+      if self.args.application:
         self.install_padding()
         self.install_tab_file("target/tab/{}.tab".format(self.args.application))
         if self.verify_flashed_app(self.args.application):
           info("You're all set!")
           return 0
-      error(("It seems that something went wrong. App/example not found "
+        error(
+            ("It seems that something went wrong. App/example not found "
              "on your board. Ensure the connections between the programmer and "
              "the board are correct."))
         return 1
+      return 0
 
     if self.args.programmer in ("pyocd", "nordicdfu", "none"):
       dest_file = "target/{}_merged.hex".format(self.args.board)
@@ -734,7 +737,14 @@ if __name__ == "__main__":
             "storage (i.e. unplugging the key will reset the key)."),
   )
 
-  apps_group = main_parser.add_mutually_exclusive_group()
+  apps_group = main_parser.add_mutually_exclusive_group(required=True)
+  apps_group.add_argument(
+      "--no-app",
+      dest="application",
+      action="store_const",
+      const=None,
+      help=("Doesn't compile nor install any application. Useful when you only "
+            "want to update Tock OS kernel."))
   apps_group.add_argument(
       "--opensk",
       dest="application",