msgproto: Support default values in get_constant() calls

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

klippy/msgproto.py

@@ -324,12 +324,16 @@ class MessageParser:
         except Exception as e:
             logging.exception("process_identify error")
             raise error("Error during identify: %s" % (str(e),))
-    def get_constant(self, name):
-        try:
-            return self.config[name]
-        except KeyError:
+    class sentinel: pass
+    def get_constant(self, name, default=sentinel):
+        if name not in self.config:
+            if default is not self.sentinel:
+                return default
             raise error("Firmware constant '%s' not found" % (name,))
-    def get_constant_float(self, name):
+        return self.config[name]
+    def get_constant_float(self, name, default=sentinel):
+        if name not in self.config and default is not self.sentinel:
+            return default
         try:
             return float(self.config[name])
         except ValueError:

klippy/serialhdl.py

@@ -90,8 +90,8 @@ class SerialReader:
         logging.info("MCU config: %s", " ".join(
             ["%s=%s" % (k, v) for k, v in msgparser.config.items()]))
         # Setup baud adjust
-        mcu_baud = float(msgparser.config.get('SERIAL_BAUD', 0.))
-        if mcu_baud:
+        mcu_baud = msgparser.get_constant_float('SERIAL_BAUD', None)
+        if mcu_baud is not None:
             baud_adjust = self.BITS_PER_BYTE / mcu_baud
             self.ffi_lib.serialqueue_set_baud_adjust(
                 self.serialqueue, baud_adjust)