X-Git-Url: https://main.carlh.net/gitweb/?a=blobdiff_plain;f=gtk2_ardour%2Fengine_dialog.cc;h=a8209514c13bb685c5587d2ff04cc79a360eb9e4;hb=refs%2Fheads%2Fcarl-master;hp=fe8a594193050712b0f7ba7b697df035a2b4b1fe;hpb=73acaf6de6c0911d62709b28ac5b756f2a2e20a3;p=ardour.git

diff --git a/gtk2_ardour/engine_dialog.cc b/gtk2_ardour/engine_dialog.cc
index fe8a594193..a8209514c1 100644
--- a/gtk2_ardour/engine_dialog.cc
+++ b/gtk2_ardour/engine_dialog.cc
@@ -1,33 +1,36 @@
 /*
-    Copyright (C) 2010 Paul Davis
-
-    This program is free software; you can redistribute it and/or modify
-    it under the terms of the GNU General Public License as published by
-    the Free Software Foundation; either version 2 of the License, or
-    (at your option) any later version.
-
-    This program is distributed in the hope that it will be useful,
-    but WITHOUT ANY WARRANTY; without even the implied warranty of
-    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-    GNU General Public License for more details.
-
-    You should have received a copy of the GNU General Public License
-    along with this program; if not, write to the Free Software
-    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
-
-*/
+ * Copyright (C) 2007-2012 Carl Hetherington <carl@carlh.net>
+ * Copyright (C) 2007-2017 Paul Davis <paul@linuxaudiosystems.com>
+ * Copyright (C) 2008-2012 David Robillard <d@drobilla.net>
+ * Copyright (C) 2013-2014 Colin Fletcher <colin.m.fletcher@googlemail.com>
+ * Copyright (C) 2013-2019 Robin Gareus <robin@gareus.org>
+ * Copyright (C) 2015-2016 Tim Mayberry <mojofunk@gmail.com>
+ * Copyright (C) 2015 Ben Loftis <ben@harrisonconsoles.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
 
 #include <exception>
 #include <vector>
 #include <cmath>
-#include <fstream>
 #include <map>
 
 #include <boost/scoped_ptr.hpp>
 
-#include <gtkmm/messagedialog.h>
-
 #include "pbd/error.h"
+#include "pbd/locale_guard.h"
 #include "pbd/xml++.h"
 #include "pbd/unwind.h"
 #include "pbd/failed_constructor.h"
@@ -37,6 +40,8 @@
 #include <gtkmm/notebook.h>
 #include <gtkmm2ext/utils.h>
 
+#include "widgets/tooltips.h"
+
 #include "ardour/audio_backend.h"
 #include "ardour/audioengine.h"
 #include "ardour/mtdm.h"
@@ -50,17 +55,22 @@
 
 #include "opts.h"
 #include "debug.h"
+#include "ardour_message.h"
 #include "ardour_ui.h"
 #include "engine_dialog.h"
 #include "gui_thread.h"
+#include "ui_config.h"
+#include "public_editor.h"
 #include "utils.h"
-#include "i18n.h"
+#include "pbd/i18n.h"
+#include "splash.h"
 
 using namespace std;
 using namespace Gtk;
 using namespace Gtkmm2ext;
 using namespace PBD;
 using namespace Glib;
+using namespace ArdourWidgets;
 using namespace ARDOUR_UI_UTILS;
 
 #define DEBUG_ECONTROL(msg) DEBUG_TRACE (PBD::DEBUG::EngineControl, string_compose ("%1: %2\n", __LINE__, msg));
@@ -88,6 +98,8 @@ EngineControl::EngineControl ()
 	, midi_devices_button (_("Midi Device Setup"))
 	, start_stop_button (_("Stop"))
 	, update_devices_button (_("Refresh Devices"))
+	, use_buffered_io_button (_("Use Buffered I/O"), ArdourButton::led_default_elements)
+	, try_autostart_button (_("Autostart"), ArdourButton::led_default_elements)
 	, lm_measure_label (_("Measure"))
 	, lm_use_button (_("Use results"))
 	, lm_back_button (_("Back to settings ... (ignore results)"))
@@ -97,6 +109,7 @@ EngineControl::EngineControl ()
 	, lm_running (false)
 	, midi_back_button (_("Back to settings"))
 	, ignore_changes (0)
+	, ignore_device_changes (0)
 	, _desired_sample_rate (0)
 	, started_at_least_once (false)
 	, queue_device_changed (false)
@@ -116,7 +129,7 @@ EngineControl::EngineControl ()
 	vector<const ARDOUR::AudioBackendInfo*> backends = ARDOUR::AudioEngine::instance()->available_backends();
 
 	if (backends.empty()) {
-		MessageDialog msg (string_compose (_("No audio/MIDI backends detected. %1 cannot run\n\n(This is a build/packaging/system error. It should never happen.)"), PROGRAM_NAME));
+		ArdourMessageDialog msg (string_compose (_("No audio/MIDI backends detected. %1 cannot run\n\n(This is a build/packaging/system error. It should never happen.)"), PROGRAM_NAME));
 		msg.run ();
 		throw failed_constructor ();
 	}
@@ -167,17 +180,25 @@ EngineControl::EngineControl ()
 	lm_table.attach (*preamble, 0, 3, row, row+1, AttachOptions(FILL|EXPAND), (AttachOptions) 0);
 	row++;
 
-	label = manage (new Label (_("Output channel")));
+	label = manage (new Label (_("Output channel:")));
 	lm_table.attach (*label, 0, 1, row, row+1, xopt, (AttachOptions) 0);
 
+	lm_output_channel_list = Gtk::ListStore::create (lm_output_channel_cols);
+	lm_output_channel_combo.set_model (lm_output_channel_list);
+	lm_output_channel_combo.pack_start (lm_output_channel_cols.pretty_name);
+
 	Gtk::Alignment* misc_align = manage (new Alignment (0.0, 0.5));
 	misc_align->add (lm_output_channel_combo);
 	lm_table.attach (*misc_align, 1, 3, row, row+1, xopt, (AttachOptions) 0);
 	++row;
 
-	label = manage (new Label (_("Input channel")));
+	label = manage (new Label (_("Input channel:")));
 	lm_table.attach (*label, 0, 1, row, row+1, xopt, (AttachOptions) 0);
 
+	lm_input_channel_list = Gtk::ListStore::create (lm_input_channel_cols);
+	lm_input_channel_combo.set_model (lm_input_channel_list);
+	lm_input_channel_combo.pack_start (lm_input_channel_cols.pretty_name);
+
 	misc_align = manage (new Alignment (0.0, 0.5));
 	misc_align->add (lm_input_channel_combo);
 	lm_table.attach (*misc_align, 1, 3, row, row+1, FILL, (AttachOptions) 0);
@@ -187,7 +208,8 @@ EngineControl::EngineControl ()
 	lm_measure_button.add (lm_measure_label);
 	lm_measure_button.signal_clicked().connect (sigc::mem_fun (*this, &EngineControl::latency_button_clicked));
 	lm_use_button.signal_clicked().connect (sigc::mem_fun (*this, &EngineControl::use_latency_button_clicked));
-	lm_back_button_signal = lm_back_button.signal_clicked().connect (sigc::bind (sigc::mem_fun (notebook, &Gtk::Notebook::set_current_page), 0));
+	lm_back_button_signal = lm_back_button.signal_clicked().connect(
+	    sigc::mem_fun(*this, &EngineControl::latency_back_button_clicked));
 
 	lm_use_button.set_sensitive (false);
 
@@ -262,7 +284,6 @@ EngineControl::EngineControl ()
 	output_channels.signal_output().connect (sigc::bind (sigc::ptr_fun (&EngineControl::print_channel_count), &output_channels));
 
 	midi_devices_button.signal_clicked.connect (mem_fun (*this, &EngineControl::configure_midi_devices));
-	midi_devices_button.set_sensitive (false);
 	midi_devices_button.set_name ("generic button");
 	midi_devices_button.set_can_focus(true);
 
@@ -275,14 +296,27 @@ EngineControl::EngineControl ()
 	start_stop_button.set_sensitive (false);
 	start_stop_button.set_name ("generic button");
 	start_stop_button.set_can_focus(true);
+	start_stop_button.set_can_default(true);
+	start_stop_button.set_act_on_release (false);
 
 	update_devices_button.signal_clicked.connect (mem_fun (*this, &EngineControl::update_devices_button_clicked));
 	update_devices_button.set_sensitive (false);
 	update_devices_button.set_name ("generic button");
 	update_devices_button.set_can_focus(true);
 
-	cancel_button = add_button (Gtk::Stock::CLOSE, Gtk::RESPONSE_CANCEL);
-	ok_button = add_button (Gtk::Stock::OK, Gtk::RESPONSE_OK);
+	use_buffered_io_button.signal_clicked.connect (mem_fun (*this, &EngineControl::use_buffered_io_button_clicked));
+	use_buffered_io_button.set_sensitive (false);
+	use_buffered_io_button.set_name ("generic button");
+	use_buffered_io_button.set_can_focus(true);
+
+	try_autostart_button.signal_clicked.connect (mem_fun (*this, &EngineControl::try_autostart_button_clicked));
+	try_autostart_button.set_name ("generic button");
+	try_autostart_button.set_can_focus(true);
+	config_parameter_changed ("try-autostart-engine");
+	set_tooltip (try_autostart_button,
+			string_compose (_("Always try these settings when starting %1, if the same device is available"), PROGRAM_NAME));
+
+	ARDOUR::Config->ParameterChanged.connect (*this, invalidator (*this), boost::bind (&EngineControl::config_parameter_changed, this, _1), gui_context());
 
 	/* Pick up any existing audio setup configuration, if appropriate */
 
@@ -301,13 +335,15 @@ EngineControl::EngineControl ()
 		set_default_state ();
 	}
 
+	update_sensitivity ();
 	connect_changed_signals ();
 
 	notebook.signal_switch_page().connect (sigc::mem_fun (*this, &EngineControl::on_switch_page));
 
 	connect_disconnect_button.signal_clicked().connect (sigc::mem_fun (*this, &EngineControl::connect_disconnect_click));
-	connect_disconnect_button.set_no_show_all();
 
+	connect_disconnect_button.set_no_show_all();
+	start_stop_button.set_no_show_all();
 }
 
 void
@@ -321,6 +357,8 @@ EngineControl::connect_changed_signals ()
 	    sigc::mem_fun (*this, &EngineControl::sample_rate_changed));
 	buffer_size_combo_connection = buffer_size_combo.signal_changed ().connect (
 	    sigc::mem_fun (*this, &EngineControl::buffer_size_changed));
+	nperiods_combo_connection = nperiods_combo.signal_changed ().connect (
+	    sigc::mem_fun (*this, &EngineControl::nperiods_changed));
 	device_combo_connection = device_combo.signal_changed ().connect (
 	    sigc::mem_fun (*this, &EngineControl::device_changed));
 	midi_option_combo_connection = midi_option_combo.signal_changed ().connect (
@@ -350,6 +388,7 @@ EngineControl::block_changed_signals ()
 		driver_combo_connection.block ();
 		sample_rate_combo_connection.block ();
 		buffer_size_combo_connection.block ();
+		nperiods_combo_connection.block ();
 		device_combo_connection.block ();
 		input_device_combo_connection.block ();
 		output_device_combo_connection.block ();
@@ -370,6 +409,7 @@ EngineControl::unblock_changed_signals ()
 		driver_combo_connection.unblock ();
 		sample_rate_combo_connection.unblock ();
 		buffer_size_combo_connection.unblock ();
+		nperiods_combo_connection.unblock ();
 		device_combo_connection.unblock ();
 		input_device_combo_connection.unblock ();
 		output_device_combo_connection.unblock ();
@@ -383,8 +423,8 @@ EngineControl::unblock_changed_signals ()
 
 EngineControl::SignalBlocker::SignalBlocker (EngineControl& engine_control,
                                              const std::string& reason)
-    : ec (engine_control)
-    , m_reason (reason)
+	: ec (engine_control)
+	, m_reason (reason)
 {
 	DEBUG_ECONTROL (string_compose ("SignalBlocker: %1", m_reason));
 	ec.block_changed_signals ();
@@ -405,51 +445,50 @@ EngineControl::on_show ()
 		backend_changed ();
 	}
 	device_changed ();
-	ok_button->grab_focus();
+	start_stop_button.grab_focus();
 }
 
 void
-EngineControl::on_response (int response_id)
+EngineControl::on_map ()
 {
-	ArdourDialog::on_response (response_id);
+	if (!ARDOUR_UI::instance()->the_session () && !PublicEditor::_instance) {
+		set_type_hint (Gdk::WINDOW_TYPE_HINT_NORMAL);
+	} else if (UIConfiguration::instance().get_all_floating_windows_are_dialogs()) {
+		set_type_hint (Gdk::WINDOW_TYPE_HINT_DIALOG);
+	} else {
+		set_type_hint (Gdk::WINDOW_TYPE_HINT_UTILITY);
+	}
+	ArdourDialog::on_map ();
+}
 
-	switch (response_id) {
-		case RESPONSE_OK:
-			if (push_state_to_backend (true) != 0) {
-				return;
-			} else {
-				hide ();
-			}
-#ifdef PLATFORM_WINDOWS
-
-			// But if there's no session open, this can produce
-			// a long gap when nothing appears to be happening.
-			// Let's show the splash image while we're waiting.
-			if ( !ARDOUR_COMMAND_LINE::no_splash ) {
-				if ( ARDOUR_UI::instance() ) {
-					if ( !ARDOUR_UI::instance()->session_loaded ) {
-						ARDOUR_UI::instance()->show_splash();
-					}
-				}
-			}
-#endif
-			break;
-		case RESPONSE_DELETE_EVENT:
-			{
-				GdkEventButton ev;
-				ev.type = GDK_BUTTON_PRESS;
-				ev.button = 1;
-				on_delete_event ((GdkEventAny*) &ev);
-				break;
-			}
-		case RESPONSE_CANCEL:
-			if (ARDOUR_UI::instance() && ARDOUR_UI::instance()->session_loaded) {
-				ARDOUR_UI::instance()->check_audioengine ();
-			}
-			// fall through
-		default:
-			hide ();
+void
+EngineControl::config_parameter_changed (std::string const & p)
+{
+	if (p == "try-autostart-engine") {
+		try_autostart_button.set_active (ARDOUR::Config->get_try_autostart_engine ());
+	}
+}
+
+bool
+EngineControl::start_engine ()
+{
+	if (push_state_to_backend (true) != 0) {
+		ArdourMessageDialog msg (*this, ARDOUR::AudioEngine::instance()->get_last_backend_error());
+		msg.run();
+		return false;
+	}
+	return true;
+}
+
+bool
+EngineControl::stop_engine (bool for_latency)
+{
+	if (ARDOUR::AudioEngine::instance()->stop(for_latency)) {
+		ArdourMessageDialog msg(*this, ARDOUR::AudioEngine::instance()->get_last_backend_error());
+		msg.run();
+		return false;
 	}
+	return true;
 }
 
 void
@@ -475,7 +514,6 @@ EngineControl::build_notebook ()
 	engine_status.show();
 
 	basic_packer.attach (start_stop_button, 3, 4, 0, 1, xopt, xopt);
-	basic_packer.attach (update_devices_button, 3, 4, 1, 2, xopt, xopt);
 
 	lm_button_audio.signal_clicked.connect (sigc::mem_fun (*this, &EngineControl::calibrate_audio_latency));
 	lm_button_audio.set_name ("generic button");
@@ -506,6 +544,8 @@ EngineControl::build_full_control_notebook ()
 	vector<string> strings;
 	AttachOptions xopt = AttachOptions (FILL|EXPAND);
 	int row = 1; // row zero == backend combo
+	int btn = 1; // row zero == start_stop_button
+	bool autostart_packed = false;
 
 	/* start packing it up */
 
@@ -537,21 +577,47 @@ EngineControl::build_full_control_notebook ()
 		output_device_combo.set_active_text ("");
 	}
 
+	/* same line as Driver */
+	if (backend->can_use_buffered_io()) {
+		basic_packer.attach (use_buffered_io_button, 3, 4, btn, btn + 1, xopt, xopt);
+		btn++;
+	}
+
+	/* same line as Device(s) */
+	if (backend->can_request_update_devices()) {
+		basic_packer.attach (update_devices_button, 3, 4, btn, btn + 1, xopt, xopt);
+		btn++;
+	}
+
+	/* prefer "try autostart" below "Start" if possible */
+	if (btn < row) {
+		basic_packer.attach (try_autostart_button, 3, 4, btn, btn + 1, xopt, xopt);
+		btn++;
+		autostart_packed = true;
+	}
+
 	label = manage (left_aligned_label (_("Sample rate:")));
 	basic_packer.attach (*label, 0, 1, row, row + 1, xopt, (AttachOptions) 0);
 	basic_packer.attach (sample_rate_combo, 1, 2, row, row + 1, xopt, (AttachOptions) 0);
 	row++;
 
-
 	label = manage (left_aligned_label (_("Buffer size:")));
 	basic_packer.attach (*label, 0, 1, row, row + 1, xopt, (AttachOptions) 0);
 	basic_packer.attach (buffer_size_combo, 1, 2, row, row + 1, xopt, (AttachOptions) 0);
 	buffer_size_duration_label.set_alignment (0.0); /* left-align */
 	basic_packer.attach (buffer_size_duration_label, 2, 3, row, row+1, SHRINK, (AttachOptions) 0);
 
-	/* button spans 2 rows */
+	int ctrl_btn_span = 1;
+	if (backend->can_set_period_size ()) {
+		row++;
+		label = manage (left_aligned_label (_("Periods:")));
+		basic_packer.attach (*label, 0, 1, row, row + 1, xopt, (AttachOptions) 0);
+		basic_packer.attach (nperiods_combo, 1, 2, row, row + 1, xopt, (AttachOptions) 0);
+		++ctrl_btn_span;
+	}
 
-	basic_packer.attach (control_app_button, 3, 4, row-1, row+1, xopt, xopt);
+	/* button spans 2 or 3 rows: Sample rate, Buffer size, Periods */
+	basic_packer.attach (control_app_button, 3, 4, row - ctrl_btn_span, row + 1, xopt, xopt);
 	row++;
 
 	input_channels.set_name ("InputChannels");
@@ -561,12 +627,12 @@ EngineControl::build_full_control_notebook ()
 	output_channels.set_editable (true);
 
 	if (!ARDOUR::Profile->get_mixbus()) {
-		label = manage (left_aligned_label (_("Input Channels:")));
+		label = manage (left_aligned_label (_("Input channels:")));
 		basic_packer.attach (*label, 0, 1, row, row+1, xopt, (AttachOptions) 0);
 		basic_packer.attach (input_channels, 1, 2, row, row+1, xopt, (AttachOptions) 0);
 		++row;
 	}
-	
+
 	output_channels.set_name ("OutputChannels");
 	output_channels.set_flags (Gtk::CAN_FOCUS);
 	output_channels.set_digits (0);
@@ -574,12 +640,19 @@ EngineControl::build_full_control_notebook ()
 	output_channels.set_editable (true);
 
 	if (!ARDOUR::Profile->get_mixbus()) {
-		label = manage (left_aligned_label (_("Output Channels:")));
+		label = manage (left_aligned_label (_("Output channels:")));
 		basic_packer.attach (*label, 0, 1, row, row+1, xopt, (AttachOptions) 0);
 		basic_packer.attach (output_channels, 1, 2, row, row+1, xopt, (AttachOptions) 0);
 		++row;
 	}
-	
+
+	/* Prefere next available vertical slot, 1 row */
+	if (btn < row && !autostart_packed) {
+		basic_packer.attach (try_autostart_button, 3, 4, btn, btn + 1, xopt, xopt);
+		btn++;
+		autostart_packed = true;
+	}
+
 	input_latency.set_name ("InputLatency");
 	input_latency.set_flags (Gtk::CAN_FOCUS);
 	input_latency.set_digits (0);
@@ -613,14 +686,12 @@ EngineControl::build_full_control_notebook ()
 	label = manage (left_aligned_label (_("MIDI System:")));
 	basic_packer.attach (*label, 0, 1, row, row + 1, xopt, (AttachOptions) 0);
 	basic_packer.attach (midi_option_combo, 1, 2, row, row + 1, SHRINK, (AttachOptions) 0);
-#if ! defined __APPLE__  && ! defined PLATFORM_WINDOWS // => linux, YAY
-	/* Currently the only backend with dedicated Midi setup is ALSA.
-	 * lot of people complain that this is greyed out
-	 * "I can't use MIDI, the setup is greyed out"
-	 */
 	basic_packer.attach (midi_devices_button, 3, 4, row, row+1, xopt, xopt);
-#endif
 	row++;
+
+	if (!autostart_packed) {
+		basic_packer.attach (try_autostart_button, 3, 4, row, row+1, xopt, xopt);
+	}
 }
 
 void
@@ -669,9 +740,8 @@ EngineControl::~EngineControl ()
 void
 EngineControl::disable_latency_tab ()
 {
-	vector<string> empty;
-	set_popdown_strings (lm_output_channel_combo, empty);
-	set_popdown_strings (lm_input_channel_combo, empty);
+	lm_input_channel_list->clear ();
+	lm_output_channel_list->clear ();
 	lm_measure_button.set_sensitive (false);
 	lm_use_button.set_sensitive (false);
 }
@@ -687,13 +757,13 @@ EngineControl::enable_latency_tab ()
 	ARDOUR::AudioEngine::instance()->get_physical_inputs (type, inputs);
 
 	if (!ARDOUR::AudioEngine::instance()->running()) {
-		MessageDialog msg (_("Failed to start or connect to audio-engine.\n\nLatency calibration requires a working audio interface."));
+		ArdourMessageDialog msg (_("Failed to start or connect to audio-engine.\n\nLatency calibration requires a working audio interface."));
 		notebook.set_current_page (0);
 		msg.run ();
 		return;
 	}
 	else if (inputs.empty() || outputs.empty()) {
-		MessageDialog msg (_("Your selected audio configuration is playback- or capture-only.\n\nLatency calibration requires playback and capture"));
+		ArdourMessageDialog msg (_("Your selected audio configuration is playback- or capture-only.\n\nLatency calibration requires playback and capture"));
 		notebook.set_current_page (0);
 		msg.run ();
 		return;
@@ -704,16 +774,37 @@ EngineControl::enable_latency_tab ()
 		lm_back_button_signal = lm_back_button.signal_clicked().connect (sigc::bind (sigc::mem_fun (notebook, &Gtk::Notebook::set_current_page), midi_tab));
 		lm_preamble.hide ();
 	} else {
-		lm_back_button_signal = lm_back_button.signal_clicked().connect (sigc::bind (sigc::mem_fun (notebook, &Gtk::Notebook::set_current_page), 0));
+		lm_back_button_signal = lm_back_button.signal_clicked().connect(
+		    sigc::mem_fun(*this, &EngineControl::latency_back_button_clicked));
 		lm_preamble.show ();
 	}
 
-	set_popdown_strings (lm_output_channel_combo, outputs);
-	lm_output_channel_combo.set_active_text (outputs.front());
+	lm_output_channel_list->clear ();
+	for (vector<string>::const_iterator i = outputs.begin(); i != outputs.end(); ++i) {
+		Gtk::TreeModel::iterator iter = lm_output_channel_list->append ();
+		Gtk::TreeModel::Row row = *iter;
+		 row[lm_output_channel_cols.port_name] = *i;
+		 std::string pn = ARDOUR::AudioEngine::instance()->get_pretty_name_by_name (*i);
+		 if (pn.empty()) {
+			 pn = (*i).substr ((*i).find (':') + 1);
+		 }
+		 row[lm_output_channel_cols.pretty_name] = pn;
+	}
+	lm_output_channel_combo.set_active (0);
 	lm_output_channel_combo.set_sensitive (true);
 
-	set_popdown_strings (lm_input_channel_combo, inputs);
-	lm_input_channel_combo.set_active_text (inputs.front());
+	lm_input_channel_list->clear ();
+	for (vector<string>::const_iterator i = inputs.begin(); i != inputs.end(); ++i) {
+		Gtk::TreeModel::iterator iter = lm_input_channel_list->append ();
+		Gtk::TreeModel::Row row = *iter;
+		 row[lm_input_channel_cols.port_name] = *i;
+		 std::string pn = ARDOUR::AudioEngine::instance()->get_pretty_name_by_name (*i);
+		 if (pn.empty()) {
+			 pn = (*i).substr ((*i).find (':') + 1);
+		 }
+		 row[lm_input_channel_cols.pretty_name] = pn;
+	}
+	lm_input_channel_combo.set_active (0);
 	lm_input_channel_combo.set_sensitive (true);
 
 	lm_measure_button.set_sensitive (true);
@@ -743,13 +834,13 @@ EngineControl::update_sensitivity ()
 {
 	boost::shared_ptr<ARDOUR::AudioBackend> backend = ARDOUR::AudioEngine::instance()->current_backend();
 	if (!backend) {
-		ok_button->set_sensitive (false);
 		start_stop_button.set_sensitive (false);
 		return;
 	}
 
 	bool valid = true;
 	size_t devices_available = 0;
+	bool engine_running = ARDOUR::AudioEngine::instance()->running();
 
 	if (backend->use_separate_input_and_output_devices ()) {
 		devices_available += get_popdown_string_count (input_device_combo);
@@ -767,29 +858,17 @@ EngineControl::update_sensitivity ()
 	} else {
 		input_latency.set_sensitive (true);
 		output_latency.set_sensitive (true);
-		input_channels.set_sensitive (true);
-		output_channels.set_sensitive (true);
+		input_channels.set_sensitive (!engine_running);
+		output_channels.set_sensitive (!engine_running);
 	}
 
 	if (get_popdown_string_count (buffer_size_combo) > 0) {
-		if (!ARDOUR::AudioEngine::instance()->running()) {
+		if (!engine_running) {
 			buffer_size_combo.set_sensitive (valid);
-		} else if (backend->can_change_sample_rate_when_running()) {
+		} else if (backend->can_change_buffer_size_when_running ()) {
 			buffer_size_combo.set_sensitive (valid || !_have_control);
 		} else {
-#if 1
-			/* TODO
-			 * Currently there is no way to manually stop the
-			 * engine in order to re-configure it.
-			 * This needs to remain sensitive for now.
-			 *
-			 * (it's also handy to implicily
-			 * re-start the engine)
-			 */
-			buffer_size_combo.set_sensitive (true);
-#else
 			buffer_size_combo.set_sensitive (false);
-#endif
 		}
 	} else {
 		buffer_size_combo.set_sensitive (false);
@@ -797,39 +876,50 @@ EngineControl::update_sensitivity ()
 	}
 
 	if (get_popdown_string_count (sample_rate_combo) > 0) {
-		if (!ARDOUR::AudioEngine::instance()->running()) {
-			sample_rate_combo.set_sensitive (true);
-		} else {
-			sample_rate_combo.set_sensitive (false);
+		bool allow_to_set_rate = false;
+		if (!engine_running) {
+			if (!ARDOUR_UI::instance()->the_session ()) {
+				// engine is not running, no session loaded -> anything goes.
+				allow_to_set_rate = true;
+			} else if (_desired_sample_rate > 0 && get_rate () != _desired_sample_rate) {
+				// only allow to change if the current setting is not the native session rate.
+				allow_to_set_rate = true;
+			}
 		}
+		sample_rate_combo.set_sensitive (allow_to_set_rate);
 	} else {
 		sample_rate_combo.set_sensitive (false);
 		valid = false;
 	}
 
+	if (get_popdown_string_count (nperiods_combo) > 0) {
+		if (!engine_running) {
+			nperiods_combo.set_sensitive (true);
+		} else {
+			nperiods_combo.set_sensitive (false);
+		}
+	} else {
+		nperiods_combo.set_sensitive (false);
+	}
+
 	if (_have_control) {
 		start_stop_button.set_sensitive(true);
 		start_stop_button.show();
-		if (ARDOUR::AudioEngine::instance()->running()) {
+		if (engine_running) {
 			start_stop_button.set_text("Stop");
 			update_devices_button.set_sensitive(false);
+			use_buffered_io_button.set_sensitive(false);
 		} else {
-			if (backend->can_request_update_devices()) {
-				update_devices_button.show();
-			} else {
-				update_devices_button.hide();
-			}
 			start_stop_button.set_text("Start");
-			update_devices_button.set_sensitive(true);
+			update_devices_button.set_sensitive (backend->can_request_update_devices ());
+			use_buffered_io_button.set_sensitive (backend->can_use_buffered_io ());
 		}
 	} else {
-		update_devices_button.set_sensitive(false);
-		update_devices_button.hide();
 		start_stop_button.set_sensitive(false);
 		start_stop_button.hide();
 	}
 
-	if (ARDOUR::AudioEngine::instance()->running() && _have_control) {
+	if (engine_running && _have_control) {
 		input_device_combo.set_sensitive (false);
 		output_device_combo.set_sensitive (false);
 		device_combo.set_sensitive (false);
@@ -845,11 +935,7 @@ EngineControl::update_sensitivity ()
 		}
 	}
 
-	if (valid || !_have_control) {
-		ok_button->set_sensitive (true);
-	} else {
-		ok_button->set_sensitive (false);
-	}
+	midi_option_combo.set_sensitive (!engine_running);
 }
 
 void
@@ -864,6 +950,18 @@ EngineControl::midi_latency_adjustment_changed (Gtk::Adjustment *a, MidiDeviceSe
 	} else {
 		device->output_latency = a->get_value();
 	}
+
+	if (ARDOUR::AudioEngine::instance()->running() && !_measure_midi) {
+		boost::shared_ptr<ARDOUR::AudioBackend> backend = ARDOUR::AudioEngine::instance()->current_backend();
+		assert (backend);
+		if (backend->can_change_systemic_latency_when_running () && device->enabled) {
+			if (for_input) {
+				backend->set_systemic_midi_input_latency (device->name, device->input_latency);
+			} else {
+				backend->set_systemic_midi_output_latency (device->name, device->output_latency);
+			}
+		}
+	}
 }
 
 void
@@ -871,6 +969,16 @@ EngineControl::midi_device_enabled_toggled (ArdourButton *b, MidiDeviceSettings
 	b->set_active (!b->get_active());
 	device->enabled = b->get_active();
 	refresh_midi_display(device->name);
+
+	if (ARDOUR::AudioEngine::instance()->running()) {
+		boost::shared_ptr<ARDOUR::AudioBackend> backend = ARDOUR::AudioEngine::instance()->current_backend();
+		assert (backend);
+		backend->set_midi_device_enabled (device->name, device->enabled);
+		if (backend->can_change_systemic_latency_when_running () && device->enabled) {
+			backend->set_systemic_midi_input_latency (device->name, device->input_latency);
+			backend->set_systemic_midi_output_latency (device->name, device->output_latency);
+		}
+	}
 }
 
 void
@@ -896,7 +1004,7 @@ EngineControl::refresh_midi_display (std::string focus)
 
 	l = manage (new Label (_("Device"))); l->show (); l->set_alignment (0.5, 0.5);
 	midi_device_table.attach (*l, 0, 1, row, row + 2, xopt, AttachOptions (0));
-	l = manage (new Label (_("Hardware Latencies"))); l->show (); l->set_alignment (0.5, 0.5);
+	l = manage (new Label (_("Systemic Latency [samples]"))); l->show (); l->set_alignment (0.5, 0.5);
 	midi_device_table.attach (*l, 1, 3, row, row + 1, xopt, AttachOptions (0));
 	row++;
 	l = manage (new Label (_("Input"))); l->show (); l->set_alignment (0.5, 0.5);
@@ -914,7 +1022,7 @@ EngineControl::refresh_midi_display (std::string focus)
 
 		m = manage (new ArdourButton ((*p)->name, ArdourButton::led_default_elements));
 		m->set_name ("midi device");
-		m->set_can_focus (Gtk::CAN_FOCUS);
+		m->set_can_focus (true);
 		m->add_events (Gdk::BUTTON_RELEASE_MASK);
 		m->set_active (enabled);
 		m->signal_clicked.connect (sigc::bind (sigc::mem_fun (*this, &EngineControl::midi_device_enabled_toggled), m, *p));
@@ -992,6 +1100,26 @@ EngineControl::backend_changed ()
 	 */
 	engine_stopped (); // set "active/inactive"
 
+	if (!_have_control) {
+		// set settings from backend that we do have control over
+		set_buffersize_popdown_strings ();
+		set_active_text_if_present (buffer_size_combo, bufsize_as_string (backend->buffer_size()));
+	}
+
+	if (_have_control && !ignore_changes) {
+		// set driver & devices
+		State state = get_matching_state (backend_combo.get_active_text());
+		if (state) {
+			DEBUG_ECONTROL ("backend-changed(): found prior state for backend");
+			PBD::Unwinder<uint32_t> protect_ignore_changes (ignore_changes, ignore_changes + 1);
+			set_current_state (state);
+		} else {
+			DEBUG_ECONTROL ("backend-changed(): no prior state for backend");
+		}
+	} else {
+		DEBUG_ECONTROL (string_compose ("backend-changed(): _have_control=%1 ignore_changes=%2", _have_control, ignore_changes));
+	}
+
 	if (!ignore_changes) {
 		maybe_display_saved_state ();
 	}
@@ -1005,6 +1133,7 @@ EngineControl::update_midi_options ()
 
 	if (midi_options.size() == 1) {
 		/* only contains the "none" option */
+		set_popdown_strings (midi_option_combo, midi_options);
 		midi_option_combo.set_sensitive (false);
 	} else {
 		if (_have_control) {
@@ -1023,7 +1152,7 @@ EngineControl::print_channel_count (Gtk::SpinButton* sb)
 	if (ARDOUR::Profile->get_mixbus()) {
 		return true;
 	}
-	
+
 	uint32_t cnt = (uint32_t) sb->get_value();
 	if (cnt == 0) {
 		sb->set_text (_("all available channels"));
@@ -1241,6 +1370,8 @@ EngineControl::driver_changed ()
 	backend->set_driver (driver_combo.get_active_text());
 	list_devices ();
 
+	// TODO load LRU device(s) for backend + driver combo
+
 	if (!ignore_changes) {
 		maybe_display_saved_state ();
 	}
@@ -1302,7 +1433,17 @@ EngineControl::set_samplerate_popdown_strings ()
 	set_popdown_strings (sample_rate_combo, s);
 
 	if (!s.empty()) {
-		if (desired.empty ()) {
+		if (ARDOUR::AudioEngine::instance()->running()) {
+			sample_rate_combo.set_active_text (rate_as_string (backend->sample_rate()));
+		} else if (ARDOUR_UI::instance()->the_session ()) {
+			float active_sr = ARDOUR_UI::instance()->the_session()->nominal_sample_rate ();
+
+			if (std::find (sr.begin (), sr.end (), active_sr) == sr.end ()) {
+				active_sr = sr.front ();
+			}
+
+			sample_rate_combo.set_active_text (rate_as_string (active_sr));
+		} else if (desired.empty ()) {
 			float new_active_sr = backend->default_sample_rate ();
 
 			if (std::find (sr.begin (), sr.end (), new_active_sr) == sr.end ()) {
@@ -1313,7 +1454,6 @@ EngineControl::set_samplerate_popdown_strings ()
 		} else {
 			sample_rate_combo.set_active_text (desired);
 		}
-
 	}
 	update_sensitivity ();
 }
@@ -1369,7 +1509,7 @@ EngineControl::set_buffersize_popdown_strings ()
 		s.push_back (bufsize_as_string (*x));
 	}
 
-	uint32_t previous_size = 0;
+	uint32_t previous_size = backend->buffer_size ();
 	if (!buffer_size_combo.get_active_text().empty()) {
 		previous_size = get_buffer_size ();
 	}
@@ -1402,6 +1542,31 @@ EngineControl::set_buffersize_popdown_strings ()
 	update_sensitivity ();
 }
 
+void
+EngineControl::set_nperiods_popdown_strings ()
+{
+	DEBUG_ECONTROL ("set_nperiods_popdown_strings");
+	boost::shared_ptr<ARDOUR::AudioBackend> backend = ARDOUR::AudioEngine::instance()->current_backend();
+	vector<uint32_t> np;
+	vector<string> s;
+
+	if (backend->can_set_period_size()) {
+		np = backend->available_period_sizes (get_driver());
+	}
+
+	for (vector<uint32_t>::const_iterator x = np.begin(); x != np.end(); ++x) {
+		s.push_back (to_string (*x));
+	}
+
+	set_popdown_strings (nperiods_combo, s);
+
+	if (!s.empty()) {
+		set_active_text_if_present (nperiods_combo, to_string (backend->period_size())); // XXX
+	}
+
+	update_sensitivity ();
+}
+
 void
 EngineControl::device_changed ()
 {
@@ -1433,7 +1598,7 @@ EngineControl::device_changed ()
 			queue_device_changed = true;
 		}
 	}
-	
+
 	//the device name must be set FIRST so ASIO can populate buffersizes and the control panel button
 	if (backend->use_separate_input_and_output_devices()) {
 		backend->set_input_device_name (device_name_in);
@@ -1450,6 +1615,7 @@ EngineControl::device_changed ()
 
 		set_samplerate_popdown_strings ();
 		set_buffersize_popdown_strings ();
+		set_nperiods_popdown_strings ();
 
 		/* TODO set min + max channel counts here */
 
@@ -1467,6 +1633,24 @@ void
 EngineControl::input_device_changed ()
 {
 	DEBUG_ECONTROL ("input_device_changed");
+
+	boost::shared_ptr<ARDOUR::AudioBackend> backend = ARDOUR::AudioEngine::instance()->current_backend();
+	if (backend && backend->match_input_output_devices_or_none ()) {
+		const std::string& dev_none = ARDOUR::AudioBackend::get_standard_device_name (ARDOUR::AudioBackend::DeviceNone);
+
+		if (get_output_device_name () != dev_none
+				&& get_input_device_name () != dev_none
+				&& get_input_device_name () != get_output_device_name ()) {
+			block_changed_signals ();
+			if (contains_value (output_device_combo, get_input_device_name ())) {
+				output_device_combo.set_active_text (get_input_device_name ());
+			} else {
+				assert (contains_value (output_device_combo, dev_none));
+				output_device_combo.set_active_text (dev_none);
+			}
+			unblock_changed_signals ();
+		}
+	}
 	device_changed ();
 }
 
@@ -1474,18 +1658,30 @@ void
 EngineControl::output_device_changed ()
 {
 	DEBUG_ECONTROL ("output_device_changed");
+	boost::shared_ptr<ARDOUR::AudioBackend> backend = ARDOUR::AudioEngine::instance()->current_backend();
+	if (backend && backend->match_input_output_devices_or_none ()) {
+		const std::string& dev_none = ARDOUR::AudioBackend::get_standard_device_name (ARDOUR::AudioBackend::DeviceNone);
+
+		if (get_input_device_name () != dev_none
+				&& get_input_device_name () != dev_none
+				&& get_input_device_name () != get_output_device_name ()) {
+			block_changed_signals ();
+			if (contains_value (input_device_combo, get_output_device_name ())) {
+				input_device_combo.set_active_text (get_output_device_name ());
+			} else {
+				assert (contains_value (input_device_combo, dev_none));
+				input_device_combo.set_active_text (dev_none);
+			}
+			unblock_changed_signals ();
+		}
+	}
 	device_changed ();
 }
 
 string
 EngineControl::bufsize_as_string (uint32_t sz)
 {
-	/* Translators: "samples" is always plural here, so no
-	   need for plural+singular forms.
-	 */
-	char buf[64];
-	snprintf (buf, sizeof (buf), "%u %s", sz, P_("sample", "samples", sz));
-	return buf;
+	return string_compose (P_("%1 sample", "%1 samples", sz), to_string(sz));
 }
 
 void
@@ -1504,6 +1700,19 @@ void
 EngineControl::buffer_size_changed ()
 {
 	DEBUG_ECONTROL ("buffer_size_changed");
+	if (ARDOUR::AudioEngine::instance()->running()) {
+		boost::shared_ptr<ARDOUR::AudioBackend> backend = ARDOUR::AudioEngine::instance()->current_backend();
+		if (backend && backend->can_change_buffer_size_when_running ()) {
+			backend->set_buffer_size (get_buffer_size());
+		}
+	}
+	show_buffer_duration ();
+}
+
+void
+EngineControl::nperiods_changed ()
+{
+	DEBUG_ECONTROL ("nperiods_changed");
 	show_buffer_duration ();
 }
 
@@ -1519,17 +1728,12 @@ EngineControl::show_buffer_duration ()
 	uint32_t samples = atoi (bs_text); /* will ignore trailing text */
 	uint32_t rate = get_rate();
 
-	/* Developers: note the hard-coding of a double buffered model
-	   in the (2 * samples) computation of latency. we always start
-	   the audiobackend in this configuration.
-	 */
-	/* note to jack1 developers: ardour also always starts the engine
-	 * in async mode (no jack2 --sync option) which adds an extra cycle
-	 * of latency with jack2 (and *3 would be correct)
-	 * The value can also be wrong if jackd is started externally..
+	/* Except for ALSA and Dummy backends, we don't know the number of periods
+	 * per cycle and settings.
 	 *
-	 * At the time of writing the ALSA backend always uses double-buffering *2,
-	 * The Dummy backend *1, and who knows what ASIO really does :)
+	 * jack1 vs jack2 have different default latencies since jack2 start
+	 * in async-mode unless --sync is given which adds an extra cycle
+	 * of latency. The value is not known if jackd is started externally..
 	 *
 	 * So just display the period size, that's also what
 	 * ARDOUR_UI::update_sample_rate() does for the status bar.
@@ -1552,7 +1756,6 @@ EngineControl::midi_option_changed ()
 
 	vector<ARDOUR::AudioBackend::DeviceStatus> midi_devices = backend->enumerate_midi_devices();
 
-	//_midi_devices.clear(); // TODO merge with state-saved settings..
 	_can_set_midi_latencies = backend->can_set_systemic_midi_latencies();
 	std::vector<MidiDeviceSettings> new_devices;
 
@@ -1586,6 +1789,17 @@ EngineControl::parameter_changed ()
 {
 }
 
+EngineControl::State
+EngineControl::get_matching_state (const string& backend)
+{
+	for (StateList::iterator i = states.begin(); i != states.end(); ++i) {
+		if ((*i)->backend == backend) {
+			return (*i);
+		}
+	}
+	return State();
+}
+
 EngineControl::State
 EngineControl::get_matching_state (
 		const string& backend,
@@ -1655,6 +1869,20 @@ bool EngineControl::equivalent_states (const EngineControl::State& state1,
 	return false;
 }
 
+// sort active first, then most recently used to the beginning of the list
+bool
+EngineControl::state_sort_cmp (const State &a, const State &b) {
+	if (a->active) {
+		return true;
+	}
+	else if (b->active) {
+		return false;
+	}
+	else {
+		return a->lru > b->lru;
+	}
+}
+
 EngineControl::State
 EngineControl::save_state ()
 {
@@ -1663,6 +1891,7 @@ EngineControl::save_state ()
 	if (!_have_control) {
 		state = get_matching_state (backend_combo.get_active_text(), string(), string());
 		if (state) {
+			state->lru = time (NULL) ;
 			return state;
 		}
 		state.reset(new StateStruct);
@@ -1682,6 +1911,8 @@ EngineControl::save_state ()
 
 	states.push_back (state);
 
+	states.sort (state_sort_cmp);
+
 	return state;
 }
 
@@ -1695,18 +1926,21 @@ EngineControl::store_state (State state)
 	state->output_device = get_output_device_name ();
 	state->sample_rate = get_rate ();
 	state->buffer_size = get_buffer_size ();
+	state->n_periods = get_nperiods ();
 	state->input_latency = get_input_latency ();
 	state->output_latency = get_output_latency ();
 	state->input_channels = get_input_channels ();
 	state->output_channels = get_output_channels ();
 	state->midi_option = get_midi_option ();
 	state->midi_devices = _midi_devices;
+	state->use_buffered_io = get_use_buffered_io ();
+	state->lru = time (NULL) ;
 }
 
 void
 EngineControl::maybe_display_saved_state ()
 {
-	if (!_have_control) {
+	if (!_have_control || ARDOUR::AudioEngine::instance()->running ()) {
 		return;
 	}
 
@@ -1716,10 +1950,12 @@ EngineControl::maybe_display_saved_state ()
 		DEBUG_ECONTROL ("Restoring saved state");
 		PBD::Unwinder<uint32_t> protect_ignore_changes (ignore_changes, ignore_changes + 1);
 
-		if (!_desired_sample_rate) {
+		if (0 == _desired_sample_rate && sample_rate_combo.get_sensitive ()) {
 			sample_rate_combo.set_active_text (rate_as_string (state->sample_rate));
 		}
 		set_active_text_if_present (buffer_size_combo, bufsize_as_string (state->buffer_size));
+
+		set_active_text_if_present (nperiods_combo, to_string(state->n_periods));
 		/* call this explicitly because we're ignoring changes to
 		   the controls at this point.
 		 */
@@ -1727,9 +1963,12 @@ EngineControl::maybe_display_saved_state ()
 		input_latency.set_value (state->input_latency);
 		output_latency.set_value (state->output_latency);
 
+		use_buffered_io_button.set_active (state->use_buffered_io);
+
 		if (!state->midi_option.empty()) {
 			midi_option_combo.set_active_text (state->midi_option);
 			_midi_devices = state->midi_devices;
+			midi_option_changed ();
 		}
 	} else {
 		DEBUG_ECONTROL ("Unable to find saved state for backend and devices");
@@ -1739,7 +1978,7 @@ EngineControl::maybe_display_saved_state ()
 XMLNode&
 EngineControl::get_state ()
 {
-	LocaleGuard lg (X_("C"));
+	LocaleGuard lg;
 
 	XMLNode* root = new XMLNode ("AudioMIDISetup");
 	std::string path;
@@ -1751,27 +1990,31 @@ EngineControl::get_state ()
 
 			XMLNode* node = new XMLNode ("State");
 
-			node->add_property ("backend", (*i)->backend);
-			node->add_property ("driver", (*i)->driver);
-			node->add_property ("device", (*i)->device);
-			node->add_property ("input-device", (*i)->input_device);
-			node->add_property ("output-device", (*i)->output_device);
-			node->add_property ("sample-rate", (*i)->sample_rate);
-			node->add_property ("buffer-size", (*i)->buffer_size);
-			node->add_property ("input-latency", (*i)->input_latency);
-			node->add_property ("output-latency", (*i)->output_latency);
-			node->add_property ("input-channels", (*i)->input_channels);
-			node->add_property ("output-channels", (*i)->output_channels);
-			node->add_property ("active", (*i)->active ? "yes" : "no");
-			node->add_property ("midi-option", (*i)->midi_option);
+			node->set_property ("backend", (*i)->backend);
+			node->set_property ("driver", (*i)->driver);
+			node->set_property ("device", (*i)->device);
+			node->set_property ("input-device", (*i)->input_device);
+			node->set_property ("output-device", (*i)->output_device);
+			node->set_property ("sample-rate", (*i)->sample_rate);
+			node->set_property ("buffer-size", (*i)->buffer_size);
+			node->set_property ("n-periods", (*i)->n_periods);
+			node->set_property ("input-latency", (*i)->input_latency);
+			node->set_property ("output-latency", (*i)->output_latency);
+			node->set_property ("input-channels", (*i)->input_channels);
+			node->set_property ("output-channels", (*i)->output_channels);
+			node->set_property ("active", (*i)->active);
+			node->set_property ("use-buffered-io", (*i)->use_buffered_io);
+			node->set_property ("midi-option", (*i)->midi_option);
+			int32_t lru_val = (*i)->active ? time (NULL) : (*i)->lru;
+			node->set_property ("lru", lru_val );
 
 			XMLNode* midi_devices = new XMLNode ("MIDIDevices");
 			for (std::vector<MidiDeviceSettings>::const_iterator p = (*i)->midi_devices.begin(); p != (*i)->midi_devices.end(); ++p) {
 				XMLNode* midi_device_stuff = new XMLNode ("MIDIDevice");
-				midi_device_stuff->add_property (X_("name"), (*p)->name);
-				midi_device_stuff->add_property (X_("enabled"), (*p)->enabled);
-				midi_device_stuff->add_property (X_("input-latency"), (*p)->input_latency);
-				midi_device_stuff->add_property (X_("output-latency"), (*p)->output_latency);
+				midi_device_stuff->set_property (X_("name"), (*p)->name);
+				midi_device_stuff->set_property (X_("enabled"), (*p)->enabled);
+				midi_device_stuff->set_property (X_("input-latency"), (*p)->input_latency);
+				midi_device_stuff->set_property (X_("output-latency"), (*p)->output_latency);
 				midi_devices->add_child_nocopy (*midi_device_stuff);
 			}
 			node->add_child_nocopy (*midi_devices);
@@ -1806,11 +2049,8 @@ EngineControl::set_state (const XMLNode& root)
 {
 	XMLNodeList          clist, cclist;
 	XMLNodeConstIterator citer, cciter;
-	XMLNode* child;
-	XMLNode* grandchild;
-	XMLProperty* prop = NULL;
-
-	fprintf (stderr, "EngineControl::set_state\n");
+	XMLNode const * child;
+	XMLNode const * grandchild;
 
 	if (root.name() != "AudioMIDISetup") {
 		return false;
@@ -1839,108 +2079,60 @@ EngineControl::set_state (const XMLNode& root)
 				continue;
 			}
 
-			if ((prop = grandchild->property ("backend")) == 0) {
-				continue;
-			}
-			state->backend = prop->value ();
-
-			if ((prop = grandchild->property ("driver")) == 0) {
-				continue;
-			}
-			state->driver = prop->value ();
-
-			if ((prop = grandchild->property ("device")) == 0) {
-				continue;
-			}
-			state->device = prop->value ();
-
-			if ((prop = grandchild->property ("input-device")) == 0) {
-				continue;
-			}
-			state->input_device = prop->value ();
-
-			if ((prop = grandchild->property ("output-device")) == 0) {
+			if (!grandchild->get_property ("backend", state->backend)) {
 				continue;
 			}
-			state->output_device = prop->value ();
 
-			if ((prop = grandchild->property ("sample-rate")) == 0) {
+			// If any of the required properties are not found in the state node
+			// then continue/skip to the next engine state
+			if (!grandchild->get_property ("driver", state->driver) ||
+			    !grandchild->get_property ("device", state->device) ||
+			    !grandchild->get_property ("input-device", state->input_device) ||
+			    !grandchild->get_property ("output-device", state->output_device) ||
+			    !grandchild->get_property ("sample-rate", state->sample_rate) ||
+			    !grandchild->get_property ("buffer-size", state->buffer_size) ||
+			    !grandchild->get_property ("input-latency", state->input_latency) ||
+			    !grandchild->get_property ("output-latency", state->output_latency) ||
+			    !grandchild->get_property ("input-channels", state->input_channels) ||
+			    !grandchild->get_property ("output-channels", state->output_channels) ||
+			    !grandchild->get_property ("active", state->active) ||
+			    !grandchild->get_property ("use-buffered-io", state->use_buffered_io) ||
+			    !grandchild->get_property ("midi-option", state->midi_option)) {
 				continue;
 			}
-			state->sample_rate = atof (prop->value ());
 
-			if ((prop = grandchild->property ("buffer-size")) == 0) {
-				continue;
+			if (!grandchild->get_property ("n-periods", state->n_periods)) {
+				// optional (new value in 4.5)
+				state->n_periods = 0;
 			}
-			state->buffer_size = atoi (prop->value ());
-
-			if ((prop = grandchild->property ("input-latency")) == 0) {
-				continue;
-			}
-			state->input_latency = atoi (prop->value ());
-
-			if ((prop = grandchild->property ("output-latency")) == 0) {
-				continue;
-			}
-			state->output_latency = atoi (prop->value ());
-
-			if ((prop = grandchild->property ("input-channels")) == 0) {
-				continue;
-			}
-			state->input_channels = atoi (prop->value ());
-
-			if ((prop = grandchild->property ("output-channels")) == 0) {
-				continue;
-			}
-			state->output_channels = atoi (prop->value ());
-
-			if ((prop = grandchild->property ("active")) == 0) {
-				continue;
-			}
-			state->active = string_is_affirmative (prop->value ());
-
-			if ((prop = grandchild->property ("midi-option")) == 0) {
-				continue;
-			}
-			state->midi_option = prop->value ();
 
 			state->midi_devices.clear();
 			XMLNode* midinode;
 			if ((midinode = ARDOUR::find_named_node (*grandchild, "MIDIDevices")) != 0) {
 				const XMLNodeList mnc = midinode->children();
 				for (XMLNodeList::const_iterator n = mnc.begin(); n != mnc.end(); ++n) {
-					if ((*n)->property (X_("name")) == 0
-							|| (*n)->property (X_("enabled")) == 0
-							|| (*n)->property (X_("input-latency")) == 0
-							|| (*n)->property (X_("output-latency")) == 0
-						 ) {
+					std::string name;
+					bool enabled;
+					uint32_t input_latency;
+					uint32_t output_latency;
+
+					if (!(*n)->get_property (X_("name"), name) ||
+					    !(*n)->get_property (X_("enabled"), enabled) ||
+					    !(*n)->get_property (X_("input-latency"), input_latency) ||
+					    !(*n)->get_property (X_("output-latency"), output_latency)) {
 						continue;
 					}
 
-					MidiDeviceSettings ptr (new MidiDeviceSetting(
-								(*n)->property (X_("name"))->value (),
-								string_is_affirmative ((*n)->property (X_("enabled"))->value ()),
-								atoi ((*n)->property (X_("input-latency"))->value ()),
-								atoi ((*n)->property (X_("output-latency"))->value ())
-								));
+					MidiDeviceSettings ptr (
+					    new MidiDeviceSetting (name, enabled, input_latency, output_latency));
 					state->midi_devices.push_back (ptr);
 				}
 			}
 
-#if 1
-			/* remove accumulated duplicates (due to bug in ealier version)
-			 * this can be removed again before release
-			 */
-			for (StateList::iterator i = states.begin(); i != states.end();) {
-				if ((*i)->backend == state->backend &&
-						(*i)->driver == state->driver &&
-						(*i)->device == state->device) {
-					i =  states.erase(i);
-				} else {
-					++i;
-				}
+			int32_t lru_val;
+			if (grandchild->get_property ("lru", lru_val)) {
+				state->lru = lru_val;
 			}
-#endif
 
 			states.push_back (state);
 		}
@@ -1948,7 +2140,7 @@ EngineControl::set_state (const XMLNode& root)
 
 	/* now see if there was an active state and switch the setup to it */
 
-	// purge states of backend that are not available in this built
+	/* purge states of backend that are not available in this built */
 	vector<const ARDOUR::AudioBackendInfo*> backends = ARDOUR::AudioEngine::instance()->available_backends();
 	vector<std::string> backend_names;
 
@@ -1963,6 +2155,30 @@ EngineControl::set_state (const XMLNode& root)
 		}
 	}
 
+	states.sort (state_sort_cmp);
+
+	/* purge old states referring to the same backend */
+	const time_t now = time (NULL);
+	for (vector<std::string>::const_iterator bi = backend_names.begin(); bi != backend_names.end(); ++bi) {
+		bool first = true;
+		for (StateList::iterator i = states.begin(); i != states.end();) {
+			if ((*i)->backend != *bi) {
+				++i; continue;
+			}
+			// keep at latest one for every audio-system
+			if (first) {
+				first = false;
+				++i; continue;
+			}
+			// also keep states used in the last 90 days.
+			if ((now - (*i)->lru) < 86400 * 90) {
+				++i; continue;
+			}
+			assert (!(*i)->active);
+			i = states.erase(i);
+		}
+	}
+
 	for (StateList::const_iterator i = states.begin(); i != states.end(); ++i) {
 
 		if ((*i)->active) {
@@ -1979,8 +2195,7 @@ EngineControl::set_current_state (const State& state)
 
 	boost::shared_ptr<ARDOUR::AudioBackend> backend;
 
-	if (!(backend = ARDOUR::AudioEngine::instance ()->set_backend (
-	          state->backend, downcase (std::string(PROGRAM_NAME)), ""))) {
+	if (!(backend = ARDOUR::AudioEngine::instance ()->set_backend (state->backend, downcase (std::string (PROGRAM_NAME)), ""))) {
 		DEBUG_ECONTROL (string_compose ("Unable to set backend to %1", state->backend));
 		// this shouldn't happen as the invalid backend names should have been
 		// removed from the list of states.
@@ -1991,6 +2206,13 @@ EngineControl::set_current_state (const State& state)
 	// do the right thing
 	backend_combo.set_active_text (state->backend);
 
+	if (!ARDOUR::AudioEngine::instance()->setup_required ()) {
+		backend_changed ();
+		// we don't have control don't restore state
+		return true;
+	}
+
+
 	if (!state->driver.empty ()) {
 		if (!backend->requires_driver_selection ()) {
 			DEBUG_ECONTROL ("Backend should require driver selection");
@@ -2053,11 +2275,15 @@ EngineControl::set_current_state (const State& state)
 	device_combo.set_active_text (state->device);
 	input_device_combo.set_active_text (state->input_device);
 	output_device_combo.set_active_text (state->output_device);
-	sample_rate_combo.set_active_text (rate_as_string (state->sample_rate));
+	if (0 == _desired_sample_rate && sample_rate_combo.get_sensitive ()) {
+		sample_rate_combo.set_active_text (rate_as_string (state->sample_rate));
+	}
 	set_active_text_if_present (buffer_size_combo, bufsize_as_string (state->buffer_size));
+	set_active_text_if_present (nperiods_combo, to_string (state->n_periods));
 	input_latency.set_value (state->input_latency);
 	output_latency.set_value (state->output_latency);
 	midi_option_combo.set_active_text (state->midi_option);
+	use_buffered_io_button.set_active (state->use_buffered_io);
 	return true;
 }
 
@@ -2066,6 +2292,7 @@ EngineControl::push_state_to_backend (bool start)
 {
 	DEBUG_ECONTROL ("push_state_to_backend");
 	boost::shared_ptr<ARDOUR::AudioBackend> backend = ARDOUR::AudioEngine::instance()->current_backend();
+	PBD::Unwinder<uint32_t> protect_ignore_device_changes (ignore_device_changes, ignore_device_changes + 1);
 
 	if (!backend) {
 		return 0;
@@ -2079,9 +2306,11 @@ EngineControl::push_state_to_backend (bool start)
 	bool change_device = false;
 	bool change_rate = false;
 	bool change_bufsize = false;
+	bool change_nperiods = false;
 	bool change_latency = false;
 	bool change_channels = false;
 	bool change_midi = false;
+	bool change_buffered_io = false;
 
 	uint32_t ochan = get_output_channels ();
 	uint32_t ichan = get_input_channels ();
@@ -2123,10 +2352,21 @@ EngineControl::push_state_to_backend (bool start)
 				change_bufsize = true;
 			}
 
+			if (backend->can_set_period_size() && get_popdown_string_count (nperiods_combo) > 0
+					&& get_nperiods() != backend->period_size()) {
+				change_nperiods = true;
+			}
+
 			if (get_midi_option() != backend->midi_option()) {
 				change_midi = true;
 			}
 
+			if (backend->can_use_buffered_io()) {
+				if (get_use_buffered_io() != backend->get_use_buffered_io()) {
+					change_buffered_io = true;
+				}
+			}
+
 			/* zero-requested channels means "all available" */
 
 			if (ichan == 0) {
@@ -2162,6 +2402,9 @@ EngineControl::push_state_to_backend (bool start)
 			change_channels = true;
 			change_latency = true;
 			change_midi = true;
+			change_buffered_io = backend->can_use_buffered_io();
+			change_channels = true;
+			change_nperiods = backend->can_set_period_size() && get_popdown_string_count (nperiods_combo) > 0;
 		}
 
 	} else {
@@ -2219,44 +2462,25 @@ EngineControl::push_state_to_backend (bool start)
 
 	/* determine if we need to stop the backend before changing parameters */
 
-	if (change_driver || change_device || change_channels || change_latency ||
+	if (change_driver || change_device || change_channels || change_nperiods ||
+			(change_latency && !backend->can_change_systemic_latency_when_running ()) ||
 			(change_rate && !backend->can_change_sample_rate_when_running()) ||
-			change_midi ||
+			change_midi || change_buffered_io ||
 			(change_bufsize && !backend->can_change_buffer_size_when_running())) {
 		restart_required = true;
 	} else {
 		restart_required = false;
 	}
 
-	if (was_running) {
-
-		if (!change_driver && !change_device && !change_channels && !change_latency && !change_midi) {
-			/* no changes in any parameters that absolutely require a
-			 * restart, so check those that might be changeable without a
-			 * restart
-			 */
-
-			if (change_rate && !backend->can_change_sample_rate_when_running()) {
-				/* can't do this while running ... */
-				restart_required = true;
-			}
-
-			if (change_bufsize && !backend->can_change_buffer_size_when_running()) {
-				/* can't do this while running ... */
-				restart_required = true;
-			}
-		}
-	}
 
 	if (was_running) {
 		if (restart_required) {
-			if (ARDOUR_UI::instance()->disconnect_from_engine ()) {
+			if (ARDOUR::AudioEngine::instance()->stop()) {
 				return -1;
 			}
 		}
 	}
 
-
 	if (change_driver && backend->set_driver (get_driver())) {
 		error << string_compose (_("Cannot set driver to %1"), get_driver()) << endmsg;
 		return -1;
@@ -2284,6 +2508,10 @@ EngineControl::push_state_to_backend (bool start)
 		error << string_compose (_("Cannot set buffer size to %1"), get_buffer_size()) << endmsg;
 		return -1;
 	}
+	if (change_nperiods && backend->set_peridod_size (get_nperiods())) {
+		error << string_compose (_("Cannot set periods to %1"), get_nperiods()) << endmsg;
+		return -1;
+	}
 
 	if (change_channels || get_input_channels() == 0 || get_output_channels() == 0) {
 		if (backend->set_input_channels (get_input_channels())) {
@@ -2310,9 +2538,15 @@ EngineControl::push_state_to_backend (bool start)
 		backend->set_midi_option (get_midi_option());
 	}
 
+	if (change_buffered_io) {
+		backend->set_use_buffered_io (use_buffered_io_button.get_active());
+	}
+
 	if (1 /* TODO */) {
 		for (vector<MidiDeviceSettings>::const_iterator p = _midi_devices.begin(); p != _midi_devices.end(); ++p) {
 			if (_measure_midi) {
+				/* Disable other MIDI devices while measuring.
+				 * This is a hack to only show ports from the selected device */
 				if (*p == _measure_midi) {
 					backend->set_midi_device_enabled ((*p)->name, true);
 				} else {
@@ -2329,7 +2563,7 @@ EngineControl::push_state_to_backend (bool start)
 	}
 
 	if (start || (was_running && restart_required)) {
-		if (ARDOUR_UI::instance()->reconnect_to_engine()) {
+		if (ARDOUR::AudioEngine::instance()->start()) {
 			return -1;
 		}
 	}
@@ -2355,6 +2589,8 @@ EngineControl::post_push ()
 		store_state(state);
 	}
 
+	states.sort (state_sort_cmp);
+
 	/* all off */
 
 	for (StateList::iterator i = states.begin(); i != states.end(); ++i) {
@@ -2405,12 +2641,25 @@ EngineControl::get_buffer_size () const
 	return samples;
 }
 
+uint32_t
+EngineControl::get_nperiods () const
+{
+	string txt = nperiods_combo.get_active_text ();
+	return atoi (txt.c_str());
+}
+
 string
 EngineControl::get_midi_option () const
 {
 	return midi_option_combo.get_active_text();
 }
 
+bool
+EngineControl::get_use_buffered_io () const
+{
+	return use_buffered_io_button.get_active();
+}
+
 uint32_t
 EngineControl::get_input_channels() const
 {
@@ -2491,6 +2740,19 @@ EngineControl::control_app_button_clicked ()
 	backend->launch_control_app ();
 }
 
+void
+EngineControl::on_response (int r)
+{
+	/* Do not run ArdourDialog::on_response() which will hide us. Leave
+	 * that to whoever invoked us, if they wish to hide us after "start".
+	 *
+	 * StartupFSM does hide us after response(); Window > Audio/MIDI Setup
+	 * does not.
+	 */
+	pop_splash ();
+	Gtk::Dialog::on_response (r);
+}
+
 void
 EngineControl::start_stop_button_clicked ()
 {
@@ -2503,8 +2765,13 @@ EngineControl::start_stop_button_clicked ()
 	if (ARDOUR::AudioEngine::instance()->running()) {
 		ARDOUR::AudioEngine::instance()->stop ();
 	} else {
-		push_state_to_backend (true);
+		/* whoever displayed this dialog is expected to do its own
+		   check on whether or not the engine is running.
+		*/
+		start_engine ();
 	}
+
+	response (RESPONSE_OK);
 }
 
 void
@@ -2521,6 +2788,27 @@ EngineControl::update_devices_button_clicked ()
 	}
 }
 
+void
+EngineControl::try_autostart_button_clicked ()
+{
+	ARDOUR::Config->set_try_autostart_engine (!try_autostart_button.get_active ());
+	try_autostart_button.set_active (ARDOUR::Config->get_try_autostart_engine ());
+}
+
+void
+EngineControl::use_buffered_io_button_clicked ()
+{
+	boost::shared_ptr<ARDOUR::AudioBackend> backend = ARDOUR::AudioEngine::instance()->current_backend();
+
+	if (!backend) {
+		return;
+	}
+
+	bool set_buffered_io = !use_buffered_io_button.get_active();
+	use_buffered_io_button.set_active (set_buffered_io);
+	backend->set_use_buffered_io (set_buffered_io);
+}
+
 void
 EngineControl::manage_control_app_sensitivity ()
 {
@@ -2543,6 +2831,11 @@ void
 EngineControl::set_desired_sample_rate (uint32_t sr)
 {
 	_desired_sample_rate = sr;
+
+	if (ARDOUR::AudioEngine::instance ()->running () && ARDOUR::AudioEngine::instance ()->sample_rate () != sr) {
+		stop_engine ();
+	}
+
 	device_changed ();
 }
 
@@ -2550,25 +2843,31 @@ void
 EngineControl::on_switch_page (GtkNotebookPage*, guint page_num)
 {
 	if (page_num == 0) {
-		cancel_button->set_sensitive (true);
 		_measure_midi.reset();
 		update_sensitivity ();
-	} else {
-		cancel_button->set_sensitive (false);
-		ok_button->set_sensitive (false);
 	}
 
 	if (page_num == midi_tab) {
 		/* MIDI tab */
 		refresh_midi_display ();
+
+		/* undo special case from push_state_to_backend() when measuring midi latency */
+		if (_measure_midi && ARDOUR::AudioEngine::instance()->running ()) {
+			boost::shared_ptr<ARDOUR::AudioBackend> backend = ARDOUR::AudioEngine::instance()->current_backend();
+			if (backend->can_change_systemic_latency_when_running ()) {
+				for (vector<MidiDeviceSettings>::const_iterator p = _midi_devices.begin(); p != _midi_devices.end(); ++p) {
+					backend->set_midi_device_enabled ((*p)->name, (*p)->enabled);
+				}
+			}
+		}
+		_measure_midi.reset();
 	}
 
 	if (page_num == latency_tab) {
 		/* latency tab */
 
 		if (ARDOUR::AudioEngine::instance()->running()) {
-			// TODO - mark as 'stopped for latency
-			ARDOUR_UI::instance()->disconnect_from_engine ();
+			stop_engine (true);
 		}
 
 		{
@@ -2607,7 +2906,6 @@ EngineControl::on_switch_page (GtkNotebookPage*, guint page_num)
 	} else {
 		if (lm_running) {
 			end_latency_detection ();
-			ARDOUR::AudioEngine::instance()->stop_latency_detection();
 		}
 	}
 }
@@ -2624,13 +2922,20 @@ EngineControl::check_audio_latency_measurement ()
 		return true;
 	}
 
+	if (mtdm->get_peak () > 0.707f) {
+		// get_peak() resets the peak-hold in the detector.
+		// this GUI callback is at 10Hz and so will be fine (test-signal is at higher freq)
+		lm_results.set_markup (string_compose (results_markup, _("Input signal is > -3dBFS. Lower the signal level (output gain, input gain) on the audio-interface.")));
+		return true;
+	}
+
 	if (mtdm->err () > 0.3) {
 		mtdm->invert ();
 		mtdm->resolve ();
 	}
 
 	char buf[256];
-	ARDOUR::framecnt_t const sample_rate = ARDOUR::AudioEngine::instance()->sample_rate();
+	ARDOUR::samplecnt_t const sample_rate = ARDOUR::AudioEngine::instance()->sample_rate();
 
 	if (sample_rate == 0) {
 		lm_results.set_markup (string_compose (results_markup, _("Disconnected from audio engine")));
@@ -2638,12 +2943,12 @@ EngineControl::check_audio_latency_measurement ()
 		return false;
 	}
 
-	int frames_total = mtdm->del();
-	int extra = frames_total - ARDOUR::AudioEngine::instance()->latency_signal_delay();
+	int samples_total = mtdm->del();
+	int extra = samples_total - ARDOUR::AudioEngine::instance()->latency_signal_delay();
 
 	snprintf (buf, sizeof (buf), "%s%d samples (%.3lf ms)\n%s%d samples (%.3lf ms)",
 			_("Detected roundtrip latency: "),
-			frames_total, frames_total * 1000.0f/sample_rate,
+			samples_total, samples_total * 1000.0f/sample_rate,
 			_("Systemic latency: "),
 			extra, extra * 1000.0f/sample_rate);
 
@@ -2684,7 +2989,7 @@ EngineControl::check_midi_latency_measurement ()
 	}
 
 	char buf[256];
-	ARDOUR::framecnt_t const sample_rate = ARDOUR::AudioEngine::instance()->sample_rate();
+	ARDOUR::samplecnt_t const sample_rate = ARDOUR::AudioEngine::instance()->sample_rate();
 
 	if (sample_rate == 0) {
 		lm_results.set_markup (string_compose (results_markup, _("Disconnected from audio engine")));
@@ -2692,11 +2997,11 @@ EngineControl::check_midi_latency_measurement ()
 		return false;
 	}
 
-	ARDOUR::framecnt_t frames_total = mididm->latency();
-	ARDOUR::framecnt_t extra = frames_total - ARDOUR::AudioEngine::instance()->latency_signal_delay();
+	ARDOUR::samplecnt_t samples_total = mididm->latency();
+	ARDOUR::samplecnt_t extra = samples_total - ARDOUR::AudioEngine::instance()->latency_signal_delay();
 	snprintf (buf, sizeof (buf), "%s%" PRId64" samples (%.1lf ms) dev: %.2f[spl]\n%s%" PRId64" samples (%.1lf ms)",
 			_("Detected roundtrip latency: "),
-			frames_total, frames_total * 1000.0f / sample_rate, mididm->deviation (),
+			samples_total, samples_total * 1000.0f / sample_rate, mididm->deviation (),
 			_("Systemic latency: "),
 			extra, extra * 1000.0f / sample_rate);
 
@@ -2738,8 +3043,8 @@ EngineControl::check_midi_latency_measurement ()
 void
 EngineControl::start_latency_detection ()
 {
-	ARDOUR::AudioEngine::instance()->set_latency_input_port (lm_input_channel_combo.get_active_text());
-	ARDOUR::AudioEngine::instance()->set_latency_output_port (lm_output_channel_combo.get_active_text());
+	ARDOUR::AudioEngine::instance()->set_latency_input_port (lm_input_channel_combo.get_active ()->get_value (lm_input_channel_cols.port_name));
+	ARDOUR::AudioEngine::instance()->set_latency_output_port (lm_output_channel_combo.get_active ()->get_value (lm_output_channel_cols.port_name));
 
 	if (ARDOUR::AudioEngine::instance()->start_latency_detection (_measure_midi ? true : false) == 0) {
 		lm_results.set_markup (string_compose (results_markup, _("Detecting ...")));
@@ -2781,19 +3086,31 @@ EngineControl::latency_button_clicked ()
 	}
 }
 
+void
+EngineControl::latency_back_button_clicked ()
+{
+	ARDOUR::AudioEngine::instance()->stop_latency_detection ();
+	notebook.set_current_page(0);
+}
+
 void
 EngineControl::use_latency_button_clicked ()
 {
+	boost::shared_ptr<ARDOUR::AudioBackend> backend = ARDOUR::AudioEngine::instance()->current_backend();
 	if (_measure_midi) {
 		ARDOUR::MIDIDM* mididm = ARDOUR::AudioEngine::instance()->mididm ();
 		if (!mididm) {
 			return;
 		}
-		ARDOUR::framecnt_t frames_total = mididm->latency();
-		ARDOUR::framecnt_t extra = frames_total - ARDOUR::AudioEngine::instance()->latency_signal_delay();
-		uint32_t one_way = max ((ARDOUR::framecnt_t) 0, extra / 2);
+		ARDOUR::samplecnt_t samples_total = mididm->latency();
+		ARDOUR::samplecnt_t extra = samples_total - ARDOUR::AudioEngine::instance()->latency_signal_delay();
+		uint32_t one_way = max ((ARDOUR::samplecnt_t) 0, extra / 2);
 		_measure_midi->input_latency = one_way;
 		_measure_midi->output_latency = one_way;
+		if (backend->can_change_systemic_latency_when_running ()) {
+			backend->set_systemic_midi_input_latency (_measure_midi->name, one_way);
+			backend->set_systemic_midi_output_latency (_measure_midi->name, one_way);
+		}
 		notebook.set_current_page (midi_tab);
 	} else {
 		MTDM* mtdm = ARDOUR::AudioEngine::instance()->mtdm ();
@@ -2807,20 +3124,24 @@ EngineControl::use_latency_button_clicked ()
 
 		input_latency_adjustment.set_value (one_way);
 		output_latency_adjustment.set_value (one_way);
+		if (backend->can_change_systemic_latency_when_running ()) {
+			backend->set_systemic_input_latency (one_way);
+			backend->set_systemic_output_latency (one_way);
+		}
 
 		/* back to settings page */
 		notebook.set_current_page (0);
-}
 	}
-
+}
 
 bool
 EngineControl::on_delete_event (GdkEventAny* ev)
 {
-	if (notebook.get_current_page() == 2) {
-		/* currently on latency tab - be sure to clean up */
+	if (lm_running || notebook.get_current_page() == 2) {
+		/* currently measuring latency - be sure to clean up */
 		end_latency_detection ();
 	}
+
 	return ArdourDialog::on_delete_event (ev);
 }
 
@@ -2833,6 +3154,10 @@ EngineControl::engine_running ()
 	set_active_text_if_present (buffer_size_combo, bufsize_as_string (backend->buffer_size()));
 	sample_rate_combo.set_active_text (rate_as_string (backend->sample_rate()));
 
+	if (backend->can_set_period_size ()) {
+		set_active_text_if_present (nperiods_combo, to_string (backend->period_size()));
+	}
+
 	connect_disconnect_button.set_label (string_compose (_("Disconnect from %1"), backend->name()));
 	connect_disconnect_button.show();
 
@@ -2866,18 +3191,40 @@ EngineControl::engine_stopped ()
 void
 EngineControl::device_list_changed ()
 {
+	if (ignore_device_changes) {
+		return;
+	}
 	PBD::Unwinder<uint32_t> protect_ignore_changes (ignore_changes, ignore_changes + 1); // ??
-	list_devices ();
+	if (!ARDOUR::AudioEngine::instance()->running()) {
+		list_devices ();
+	}
+
 	midi_option_changed();
+
+	if (notebook.get_current_page() == midi_tab) {
+		if (_midi_devices.empty ()) {
+			notebook.set_current_page (0);
+		} else {
+			refresh_midi_display ();
+		}
+	}
 }
 
 void
 EngineControl::connect_disconnect_click()
 {
 	if (ARDOUR::AudioEngine::instance()->running()) {
-		ARDOUR_UI::instance()->disconnect_from_engine ();
+		stop_engine ();
 	} else {
-		ARDOUR_UI::instance()->reconnect_to_engine ();
+		if (!ARDOUR_UI::instance()->the_session ()) {
+			pop_splash ();
+			hide ();
+			ARDOUR::GUIIdle ();
+		}
+		start_engine ();
+		if (!ARDOUR_UI::instance()->the_session ()) {
+			ArdourDialog::response (RESPONSE_OK);
+		}
 	}
 }