Return to device list when device is unplugged

There was a bug where a device could end up being programmed with 0
current if the device was disconnected and reconnected while editing its
configuration.  I thought of several solutions for this, but concluded
that the right one would really be to go ahead with my original plan to
kick the user out of the configuration screen when the device was
unplugged.  As usual, the implementation could be better, but it works.

pd-buddy-gtk.py

 from gi.repository import Gtk, Gio, GObject, GLib
 
 
-def pdb_send_message(window, sp, message):
+def pdb_send_message(sp, message, window=None):
     """Send a message over the serial port and return the response"""
     try:
         # Open the serial port
         answer = answer[1:-1]
         return answer
     except OSError as e:
-        dialog = Gtk.MessageDialog(window, 0, Gtk.MessageType.ERROR,
-                Gtk.ButtonsType.CLOSE, "Error communicating with device")
-        dialog.format_secondary_text(e.strerror)
-        dialog.run()
+        if window is not None:
+            dialog = Gtk.MessageDialog(window, 0, Gtk.MessageType.ERROR,
+                    Gtk.ButtonsType.CLOSE, "Error communicating with device")
+            dialog.format_secondary_text(e.strerror)
+            dialog.run()
 
-        dialog.destroy()
+            dialog.destroy()
         raise
 
 
         self._builder.get_object("select-list").bind_model(model, func)
         self._model = model
 
-        self._reload()
-        GLib.timeout_add(1000, self._reload)
+        self.reload()
+        GLib.timeout_add(1000, self.reload)
 
-    def _reload(self):
+    def reload(self):
         self._model.update_items()
 
         # Set the visible child
     def on_identify_clicked(self, button):
         window = self.get_toplevel()
         try:
-            pdb_send_message(window, self.model.serport, 'identify')
+            pdb_send_message(self.model.serport, 'identify', window)
         except:
             return
 
         self.serial_port = None
         self.voltage = None
         self.current = None
+        self.selectlist = None
 
     def on_pdb_window_realize(self, *args):
         # Get the list
         sb = self.builder.get_object("select-box")
-        sl = SelectList()
-        sb.pack_start(sl, True, True, 0)
+        self.selectlist = SelectList()
+        sb.pack_start(self.selectlist, True, True, 0)
 
         liststore = SelectListStore()
 
-        sl.bind_model(liststore, SelectListRow)
+        self.selectlist.bind_model(liststore, SelectListRow)
 
-        sl.connect("row-activated", self.on_select_list_row_activated)
+        self.selectlist.connect("row-activated", self.on_select_list_row_activated)
 
     def on_pdb_window_delete_event(self, *args):
         Gtk.main_quit(*args)
 
         window = self.builder.get_object("pdb-window")
         try:
-            pdb_send_message(window, self.serial_port, 'load')
-            tmpcfg = pdb_send_message(window, self.serial_port, 'get_tmpcfg')
+            pdb_send_message(self.serial_port, 'load', window)
+            tmpcfg = pdb_send_message(self.serial_port, 'get_tmpcfg', window)
         except:
             return
 
         sink = self.builder.get_object("sink")
         st.set_visible_child(sink)
 
+        # Ping the Sink repeatedly
+        GLib.timeout_add(1000, self._ping)
+
+    def _ping(self):
+        """Ping the device we're configuring, showing to the list on failure"""
+        if self.serial_port is None:
+            self.selectlist.reload()
+            self.on_header_sink_back_clicked(None)
+            return False
+        try:
+            pdb_send_message(self.serial_port, '')
+            return True
+        except:
+            self.selectlist.reload()
+            self.on_header_sink_back_clicked(None)
+            return False
+
     def on_header_sink_back_clicked(self, data):
         self.serial_port = None
 
     def on_header_sink_save_clicked(self, button):
         window = self.builder.get_object("pdb-window")
         try:
-            pdb_send_message(window, self.serial_port, 'write')
+            pdb_send_message(self.serial_port, 'write', window)
 
             self._store_device_settings()
             self._set_save_button_visibility()
     def on_voltage_combobox_changed(self, combo):
         window = self.builder.get_object("pdb-window")
         try:
-            pdb_send_message(window, self.serial_port,
-                             'set_v {}'.format(int(combo.get_active_text())*1000))
+            pdb_send_message(self.serial_port,
+                             'set_v {}'.format(int(combo.get_active_text())*1000),
+                             window)
 
             self._set_save_button_visibility()
         except:
     def on_current_spinbutton_changed(self, spin):
         window = self.builder.get_object("pdb-window")
         try:
-            pdb_send_message(window, self.serial_port,
-                             'set_i {}'.format(int(spin.get_value()*1000)))
+            pdb_send_message(self.serial_port,
+                             'set_i {}'.format(int(spin.get_value()*1000)),
+                             window)
 
             self._set_save_button_visibility()
         except: