fix mistaken "do not roll" conclusion in TransportFSM::compute_should_roll()
[ardour.git] / gtk2_ardour / engine_dialog.cc
index 3019c169d86ec3feffd4e31c13ca36143beba8bc..a8209514c13bb685c5587d2ff04cc79a360eb9e4 100644 (file)
@@ -1,21 +1,26 @@
 /*
-    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>
@@ -24,9 +29,8 @@
 
 #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"
@@ -36,6 +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"
 
 #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));
@@ -87,6 +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)"))
@@ -96,6 +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)
@@ -115,7 +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 ();
        }
@@ -166,17 +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);
@@ -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 ();
@@ -405,15 +445,35 @@ EngineControl::on_show ()
                backend_changed ();
        }
        device_changed ();
-       ok_button->grab_focus();
+       start_stop_button.grab_focus();
+}
+
+void
+EngineControl::on_map ()
+{
+       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 ();
+}
+
+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) {
-               MessageDialog msg(*this,
-                                 ARDOUR::AudioEngine::instance()->get_last_backend_error());
+       if (push_state_to_backend (true) != 0) {
+               ArdourMessageDialog msg (*this, ARDOUR::AudioEngine::instance()->get_last_backend_error());
                msg.run();
                return false;
        }
@@ -421,60 +481,16 @@ EngineControl::start_engine ()
 }
 
 bool
-EngineControl::stop_engine ()
+EngineControl::stop_engine (bool for_latency)
 {
-       if (ARDOUR::AudioEngine::instance()->stop()) {
-               MessageDialog msg(*this,
-                                 ARDOUR::AudioEngine::instance()->get_last_backend_error());
+       if (ARDOUR::AudioEngine::instance()->stop(for_latency)) {
+               ArdourMessageDialog msg(*this, ARDOUR::AudioEngine::instance()->get_last_backend_error());
                msg.run();
                return false;
        }
        return true;
 }
 
-void
-EngineControl::on_response (int response_id)
-{
-       ArdourDialog::on_response (response_id);
-
-       switch (response_id) {
-       case RESPONSE_OK:
-               if (!start_engine()) {
-                       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(*this);
-               }
-       // fall through
-       default:
-               hide();
-       }
-}
-
 void
 EngineControl::build_notebook ()
 {
@@ -498,7 +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");
@@ -529,6 +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 */
 
@@ -560,21 +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");
@@ -584,7 +627,7 @@ 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;
@@ -597,12 +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);
@@ -636,14 +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
@@ -692,9 +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);
 }
@@ -710,13 +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;
@@ -732,12 +779,32 @@ EngineControl::enable_latency_tab ()
                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);
@@ -767,13 +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);
@@ -791,29 +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);
@@ -821,39 +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);
@@ -869,11 +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
@@ -888,6 +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
@@ -895,6 +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
@@ -920,7 +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);
@@ -938,7 +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));
@@ -1018,6 +1102,7 @@ EngineControl::backend_changed ()
 
        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()));
        }
 
@@ -1025,9 +1110,14 @@ EngineControl::backend_changed ()
                // 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) {
@@ -1043,6 +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) {
@@ -1342,7 +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 ()) {
@@ -1353,7 +1454,6 @@ EngineControl::set_samplerate_popdown_strings ()
                } else {
                        sample_rate_combo.set_active_text (desired);
                }
-
        }
        update_sensitivity ();
 }
@@ -1409,7 +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 ();
        }
@@ -1442,6 +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 ()
 {
@@ -1490,6 +1615,7 @@ EngineControl::device_changed ()
 
                set_samplerate_popdown_strings ();
                set_buffersize_popdown_strings ();
+               set_nperiods_popdown_strings ();
 
                /* TODO set min + max channel counts here */
 
@@ -1507,6 +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 ();
 }
 
@@ -1514,18 +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
@@ -1544,6 +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 ();
 }
 
@@ -1559,17 +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.
@@ -1592,7 +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;
 
@@ -1706,6 +1869,7 @@ 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) {
@@ -1715,7 +1879,7 @@ EngineControl::state_sort_cmp (const State &a, const State &b) {
                return false;
        }
        else {
-               return a->lru < b->lru;
+               return a->lru > b->lru;
        }
 }
 
@@ -1762,19 +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;
        }
 
@@ -1784,10 +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.
                 */
@@ -1795,9 +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");
@@ -1807,7 +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;
@@ -1819,28 +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->add_property ("lru", (*i)->active ? time (NULL) : (*i)->lru);
+                       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);
@@ -1875,11 +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;
@@ -1908,112 +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) {
-                               continue;
-                       }
-                       state->output_device = prop->value ();
-
-                       if ((prop = grandchild->property ("sample-rate")) == 0) {
-                               continue;
-                       }
-                       state->sample_rate = atof (prop->value ());
-
-                       if ((prop = grandchild->property ("buffer-size")) == 0) {
-                               continue;
-                       }
-                       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) {
+                       if (!grandchild->get_property ("backend", state->backend)) {
                                continue;
                        }
-                       state->output_latency = atoi (prop->value ());
 
-                       if ((prop = grandchild->property ("input-channels")) == 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->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;
+                       if (!grandchild->get_property ("n-periods", state->n_periods)) {
+                               // optional (new value in 4.5)
+                               state->n_periods = 0;
                        }
-                       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 ((prop = grandchild->property ("lru"))) {
-                               state->lru = atoi (prop->value ());
-                       }
-
-#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);
                }
@@ -2021,7 +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;
 
@@ -2038,6 +2157,28 @@ 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) {
@@ -2054,8 +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.
@@ -2135,11 +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;
 }
 
@@ -2148,6 +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;
@@ -2161,9 +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 ();
@@ -2205,10 +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) {
@@ -2244,6 +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 {
@@ -2301,15 +2462,17 @@ 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 (restart_required) {
                        if (ARDOUR::AudioEngine::instance()->stop()) {
@@ -2345,6 +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())) {
@@ -2371,9 +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 {
@@ -2468,12 +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
 {
@@ -2554,6 +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 ()
 {
@@ -2566,8 +2765,13 @@ EngineControl::start_stop_button_clicked ()
        if (ARDOUR::AudioEngine::instance()->running()) {
                ARDOUR::AudioEngine::instance()->stop ();
        } else {
+               /* 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
@@ -2584,6 +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 ()
 {
@@ -2606,6 +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 ();
 }
 
@@ -2613,25 +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
-                       stop_engine ();
+                       stop_engine (true);
                }
 
                {
@@ -2670,7 +2906,6 @@ EngineControl::on_switch_page (GtkNotebookPage*, guint page_num)
        } else {
                if (lm_running) {
                        end_latency_detection ();
-                       ARDOUR::AudioEngine::instance()->stop_latency_detection();
                }
        }
 }
@@ -2687,13 +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")));
@@ -2701,12 +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);
 
@@ -2747,7 +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")));
@@ -2755,11 +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);
 
@@ -2801,8 +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 ...")));
@@ -2847,23 +3089,28 @@ EngineControl::latency_button_clicked ()
 void
 EngineControl::latency_back_button_clicked ()
 {
-       ARDOUR::AudioEngine::instance()->stop(true);
+       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 ();
@@ -2877,6 +3124,10 @@ 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);
@@ -2886,10 +3137,11 @@ EngineControl::use_latency_button_clicked ()
 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);
 }
 
@@ -2902,6 +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();
 
@@ -2935,9 +3191,23 @@ 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
@@ -2946,7 +3216,15 @@ EngineControl::connect_disconnect_click()
        if (ARDOUR::AudioEngine::instance()->running()) {
                stop_engine ();
        } else {
+               if (!ARDOUR_UI::instance()->the_session ()) {
+                       pop_splash ();
+                       hide ();
+                       ARDOUR::GUIIdle ();
+               }
                start_engine ();
+               if (!ARDOUR_UI::instance()->the_session ()) {
+                       ArdourDialog::response (RESPONSE_OK);
+               }
        }
 }