Squashed commit of the following:

commit 85fae473bb30373e5675f6fcf6d97148739fb94e
Merge: bf91d35 854942d
Author: Mike Brady <mikebrady@eircom.net>
Date:   Tue Jun 4 22:15:37 2019 +0100

    Merge pull request #860 from joerg-krause/patch-2

    Debug requested period size value

commit 854942df9232fce0bc375dc94eae8a4ed5f19b20
Author: Jörg Krause <joerg.krause@embedded.rocks>
Date:   Tue Jun 4 20:47:43 2019 +0200

    Debug requested period size value

commit bf91d35bfb6b4ea65abefe5ac915c5f8dc29b2e6
Author: Mike Brady <mikebrady@eircom.net>
Date:   Tue Jun 4 15:33:30 2019 +0100

    Update RELEASENOTES-DEVELOPMENT.md

commit 3ca3408255c042d47d1a3acfa4361fb1ee72b1d8
Author: Mike Brady <mikebrady@eircom.net>
Date:   Tue Jun 4 15:32:10 2019 +0100

    Fix error message for invalid standby mode choice

commit 4bafe1c982e33392e72e16068c1005b3c6c5fe07
Author: Mike Brady <mikebrady@eircom.net>
Date:   Mon Jun 3 10:03:54 2019 +0100

    quieten a compilation warning

commit 9d96906402529045934ed24d0a5909378b886d36
Author: Mike Brady <mikebrady@eircom.net>
Date:   Sun Jun 2 18:05:40 2019 +0100

    Update configure.ac

commit 0c5c4bfe3f9618f63695b3127404272b1ec81a06
Author: Mike Brady <mikebrady@eircom.net>
Date:   Sun Jun 2 18:04:51 2019 +0100

    Update RELEASENOTES-DEVELOPMENT.md

commit 85cc1bdd97991547424e646483b3e0fcd78f1137
Author: Mike Brady <mikebrady@eircom.net>
Date:   Sun Jun 2 17:56:47 2019 +0100

    Fix the dither calculation -- it was 12 dB too high, really noticable on the U8 setting.

commit 25f0fbc24da7f115bb6a509259b8c5993460f3bc
Author: Mike Brady <mikebrady@eircom.net>
Date:   Sun Jun 2 13:42:19 2019 +0100

    Update INSTALL.md

commit d91e41d976e3ea15f441eb96b2d6446b84586882
Author: Mike Brady <mikebrady@eircom.net>
Date:   Wed May 29 17:26:44 2019 +0100

    Add missing support for S32_LE, S32_BE, S24_LE and S24_LE formats.

commit 7f2e6b1aac6740168c7fac5b1054ed234e420159
Author: Mike Brady <mikebrady@eircom.net>
Date:   Wed May 29 16:18:51 2019 +0100

    Add support for S32_LE, S32_BE, S24_LE and S24_BE wqhen generating frames of dithered silence

commit 76ad4e6a73709f6c42bd9a8ccd6a85844096719e
Author: Mike Brady <mikebrady@eircom.net>
Date:   Wed May 29 16:00:47 2019 +0100

    enable specification of specific formats and/or speeds to turn off automatic format/speed selection, fixing a bug. Clarify some of the warnings. Fix a few typos in the configuration file sample.

commit a8222e3f8531f28580130cc4009a33f497da6a59
Merge: c677006 19fbede
Author: Mike Brady <mikebrady@eircom.net>
Date:   Mon May 27 09:30:57 2019 +0100

    Merge pull request #855 from idcrook/conf_mqtt_port

    mqtt port config changes – fix error in the configuration file and check port number for sanity.
    Many thanks, David. It'll find it's easy into the next release.

commit 19fbededcfc77c83ca2c076026412157ee5fc956
Author: David Crook <idcrook@users.noreply.github.com>
Date:   Sat May 25 13:01:22 2019 -0600

    mqtt port config changes

    1. update example shairport-sync.conf file
    2. update config file mqtt port parsing

    Signed-off-by: David Crook <idcrook@users.noreply.github.com>

commit c677006541e93c5a40406accc670d9a65e68cbb9
Merge: 744c595 3c4a878
Author: Mike Brady <mikebrady@eircom.net>
Date:   Fri May 24 17:37:26 2019 +0100

    Bring into line with master 3.3

6 files changed, 120 insertions, 50 deletions

diff --git a/INSTALL.md b/INSTALL.md
index 33058c8..8d8dc7d 100644
--- a/INSTALL.md
+++ b/INSTALL.md
@@ -9,7 +9,6 @@ Do the usual update and upgrade:
 ```
 # apt-get update
 # apt-get upgrade
-# rpi-update
 ``` 
 (Separately, if you haven't done so already, consider using the `raspi-config` tool to expand the file system to use the entire card.)
 
diff --git a/audio_alsa.c b/audio_alsa.c
index cd692f1..956deba 100644
--- a/audio_alsa.c
+++ b/audio_alsa.c
@@ -192,7 +192,9 @@ static void help(void) {
          "    -c mixer-control    set the mixer control name, default is to use no mixer.\n"
          "    -m mixer-device     set the mixer device, default is the output device.\n"
          "    -i mixer-index      set the mixer index, default is 0.\n");
-  system("if [ -d /proc/asound ] ; then echo \"    hardware output devices:\" ; ls -al /proc/asound/ 2>/dev/null | grep '\\->' | tr -s ' ' | cut -d ' ' -f 9 | while read line; do echo \"      \\\"hw:$line\\\"\" ; done ; fi");
+  int r = system("if [ -d /proc/asound ] ; then echo \"    hardware output devices:\" ; ls -al /proc/asound/ 2>/dev/null | grep '\\->' | tr -s ' ' | cut -d ' ' -f 9 | while read line; do echo \"      \\\"hw:$line\\\"\" ; done ; fi");
+  if (r != 0)
+    debug(2, "error %d executing a script to list alsa hardware device names", r);
 }
 
 void set_alsa_out_dev(char *dev) { alsa_out_dev = dev; }
@@ -510,7 +512,7 @@ int actual_open_alsa_device(int do_auto_setup) {
 	}
   
   if (set_period_size_request != 0) {
-    debug(1, "Attempting to set the period size");
+    debug(1, "Attempting to set the period size to %lu", period_size_requested);
     ret = snd_pcm_hw_params_set_period_size_near(alsa_handle, alsa_params, &period_size_requested,
                                                  &dir);
     if (ret < 0) {
@@ -1037,6 +1039,8 @@ static int init(int argc, char **argv) {
 
     /* Get the output format, using the same names as aplay does*/
     if (config_lookup_string(config.cfg, "alsa.output_format", &str)) {
+    	int temp_output_format_auto_requested = config.output_format_auto_requested;
+    	config.output_format_auto_requested = 0; // assume a valid format will be given.
       if (strcasecmp(str, "S16") == 0)
         config.output_format = SPS_FORMAT_S16;
       else if (strcasecmp(str, "S16_LE") == 0)
@@ -1066,11 +1070,12 @@ static int init(int argc, char **argv) {
       else if (strcasecmp(str, "auto") == 0)
         config.output_format_auto_requested = 1;
       else {
-        warn("Invalid output format \"%s\". It should be \"U8\", \"S8\", "
+      	config.output_format_auto_requested = temp_output_format_auto_requested; //format was invalid; recall the original setting
+        warn("Invalid output format \"%s\". It should be \"auto\", \"U8\", \"S8\", "
              "\"S16\", \"S24\", \"S24_LE\", \"S24_BE\", "
              "\"S24_3LE\", \"S24_3BE\" or "
-             "\"S32\", \"S32_LE\", \"S32_BE\". It is set to \"%s\".",
-             sps_format_description_string(config.output_format));
+             "\"S32\", \"S32_LE\", \"S32_BE\". It remains set to \"%s\".", str,
+             config.output_format_auto_requested == 1 ? "auto" : sps_format_description_string(config.output_format));
       }
     }
 
@@ -1078,25 +1083,35 @@ static int init(int argc, char **argv) {
 			if (strcasecmp(str, "auto") == 0) {
 				config.output_rate_auto_requested = 1;
 			} else {
-				/* Get the output rate, which must be a multiple of 44,100*/
-				if (config_lookup_int(config.cfg, "alsa.output_rate", &value)) {
-					debug(1, "alsa output rate is %d frames per second", value);
-					switch (value) {
-					case 44100:
-					case 88200:
-					case 176400:
-					case 352800:
-						config.output_rate = value;
-						break;
-					default:
-						warn("Invalid output rate \"%d\". It should be \"auto\" or a multiple of 44,100 up "
-								 "to 352,800. It is "
-								 "set to %d.",
-								 value,config.output_rate);
-					}
-				}
+				if (config.output_rate_auto_requested == 1)
+					warn("Invalid output rate \"%s\". It should be \"auto\", 44100, 88200, 176400 or 352800. "
+						 "It remains set to \"auto\". Note: numbers should not be placed in quotes.", str);
+				else
+					warn("Invalid output rate \"%s\". It should be \"auto\", 44100, 88200, 176400 or 352800. "
+						 "It remains set to %d. Note: numbers should not be placed in quotes.", str, config.output_rate);
 			}
-    }
+		}
+		
+		/* Get the output rate, which must be a multiple of 44,100*/
+		if (config_lookup_int(config.cfg, "alsa.output_rate", &value)) {
+			debug(1, "alsa output rate is %d frames per second", value);
+			switch (value) {
+			case 44100:
+			case 88200:
+			case 176400:
+			case 352800:
+				config.output_rate = value;
+				config.output_rate_auto_requested = 0;
+				break;
+			default:
+				if (config.output_rate_auto_requested == 1)
+					warn("Invalid output rate \"%d\". It should be \"auto\", 44100, 88200, 176400 or 352800. "
+						 "It remains set to \"auto\".",value);
+				else
+					warn("Invalid output rate \"%d\".It should be \"auto\", 44100, 88200, 176400 or 352800. "
+						 "It remains set to %d.", value, config.output_rate);
+			}
+		}
 
     /* Get the use_mmap_if_available setting. */
     if (config_lookup_string(config.cfg, "alsa.use_mmap_if_available", &str)) {
@@ -1107,7 +1122,7 @@ static int init(int argc, char **argv) {
       else {
         warn("Invalid use_mmap_if_available option choice \"%s\". It should be "
              "\"yes\" or \"no\". "
-             "It is set to \"yes\".");
+             "It remains set to \"yes\".");
         config.no_mmap = 0;
       }
     }
@@ -1163,7 +1178,7 @@ static int init(int argc, char **argv) {
       else {
         warn("Invalid disable_standby_mode option choice \"%s\". It should be "
              "\"always\", \"auto\" or \"never\". "
-             "It is set to \"never\".");
+             "It remains set to \"never\".", str);
       }
     }
 
@@ -1179,7 +1194,7 @@ static int init(int argc, char **argv) {
       else {
         warn("Invalid use_precision_timing option choice \"%s\". It should be "
              "\"yes\", \"auto\" or \"no\". "
-             "It is set to \"auto\".");
+             "It remains set to \"%s\".", config.use_precision_timing == YNA_NO ? "no" : config.use_precision_timing == YNA_AUTO ? "auto" : "yes");
       }
     }
 
diff --git a/common.c b/common.c
index b097dda..9775b07 100644
--- a/common.c
+++ b/common.c
@@ -1376,12 +1376,14 @@ int64_t generate_zero_frames(char *outp, size_t number_of_frames, enum sps_forma
 
     int64_t hyper_sample = 0;
     // add a TPDF dither -- see
-    // http://www.users.qwest.net/%7Evolt42/cadenzarecording/DitherExplained.pdf
+    // http://educypedia.karadimov.info/library/DitherExplained.pdf
     // and the discussion around https://www.hydrogenaud.io/forums/index.php?showtopic=16963&st=25
 
     // I think, for a 32 --> 16 bits, the range of
     // random numbers needs to be from -2^16 to 2^16, i.e. from -65536 to 65536 inclusive, not from
     // -32768 to +32767
+    
+    // Actually, what would be generated here is from -65535 to 65535, i.e. one less on the limits.
 
     // See the original paper at
     // http://www.ece.rochester.edu/courses/ECE472/resources/Papers/Lipshitz_1992.pdf
@@ -1392,23 +1394,23 @@ int64_t generate_zero_frames(char *outp, size_t number_of_frames, enum sps_forma
     case SPS_FORMAT_S32:
     case SPS_FORMAT_S32_LE:
     case SPS_FORMAT_S32_BE:
-      dither_mask = (int64_t)1 << (64 + 1 - 32);
+      dither_mask = (int64_t)1 << (64 - 32);
       break;
     case SPS_FORMAT_S24:
     case SPS_FORMAT_S24_LE:
     case SPS_FORMAT_S24_BE:
     case SPS_FORMAT_S24_3LE:
     case SPS_FORMAT_S24_3BE:
-      dither_mask = (int64_t)1 << (64 + 1 - 24);
+      dither_mask = (int64_t)1 << (64 - 24);
       break;
     case SPS_FORMAT_S16:
     case SPS_FORMAT_S16_LE:
     case SPS_FORMAT_S16_BE:
-      dither_mask = (int64_t)1 << (64 + 1 - 16);
+      dither_mask = (int64_t)1 << (64 - 16);
       break;
     case SPS_FORMAT_S8:
     case SPS_FORMAT_U8:
-      dither_mask = (int64_t)1 << (64 + 1 - 8);
+      dither_mask = (int64_t)1 << (64 - 8);
       break;
     case SPS_FORMAT_UNKNOWN:
       die("Unexpected SPS_FORMAT_UNKNOWN while calculating dither mask.");
@@ -1442,6 +1444,30 @@ int64_t generate_zero_frames(char *outp, size_t number_of_frames, enum sps_forma
       *(int32_t *)op = hyper_sample;
       result = 4;
       break;
+    case SPS_FORMAT_S32_LE:
+      hyper_sample >>= (64 - 32);
+      byt = (uint8_t)hyper_sample;
+      *op++ = byt;
+      byt = (uint8_t)(hyper_sample >> 8);
+      *op++ = byt;
+      byt = (uint8_t)(hyper_sample >> 16);
+      *op++ = byt;
+      byt = (uint8_t)(hyper_sample >> 24);
+      *op++ = byt;
+      result = 4;
+      break;
+    case SPS_FORMAT_S32_BE:
+      hyper_sample >>= (64 - 32);
+      byt = (uint8_t)(hyper_sample >> 24);
+      *op++ = byt;
+      byt = (uint8_t)(hyper_sample >> 16);
+      *op++ = byt;
+      byt = (uint8_t)(hyper_sample >> 8);
+      *op++ = byt;
+      byt = (uint8_t)hyper_sample;
+      *op++ = byt;
+      result = 4;
+      break;
     case SPS_FORMAT_S24_3LE:
       hyper_sample >>= (64 - 24);
       byt = (uint8_t)hyper_sample;
@@ -1467,6 +1493,28 @@ int64_t generate_zero_frames(char *outp, size_t number_of_frames, enum sps_forma
       *(int32_t *)op = hyper_sample;
       result = 4;
       break;
+    case SPS_FORMAT_S24_LE:
+      hyper_sample >>= (64 - 24);
+      byt = (uint8_t)hyper_sample;
+      *op++ = byt;
+      byt = (uint8_t)(hyper_sample >> 8);
+      *op++ = byt;
+      byt = (uint8_t)(hyper_sample >> 16);
+      *op++ = byt;
+      *op++ = 0;
+      result = 4;
+      break;
+    case SPS_FORMAT_S24_BE:
+      hyper_sample >>= (64 - 24);
+      *op++ = 0;
+      byt = (uint8_t)(hyper_sample >> 16);
+      *op++ = byt;
+      byt = (uint8_t)(hyper_sample >> 8);
+      *op++ = byt;
+      byt = (uint8_t)hyper_sample;
+      *op++ = byt;
+      result = 4;
+      break;
     case SPS_FORMAT_S16_LE:
       hyper_sample >>= (64 - 16);
       byt = (uint8_t)hyper_sample;
@@ -1501,7 +1549,7 @@ int64_t generate_zero_frames(char *outp, size_t number_of_frames, enum sps_forma
       break;
     default:
       result = 0; // stop a compiler warning
-      die("Unexpected SPS_FORMAT_UNKNOWN while outputting samples");
+      die("Unexpected SPS_FORMAT_* with index %d while outputting silence",format);
     }
     p += result;
     previous_random_number = r;
diff --git a/player.c b/player.c
index 08c9203..92bda3a 100644
--- a/player.c
+++ b/player.c
@@ -650,12 +650,14 @@ static inline void process_sample(int32_t sample, char **outp, enum sps_format_t
   if (dither) {
 
     // add a TPDF dither -- see
-    // http://www.users.qwest.net/%7Evolt42/cadenzarecording/DitherExplained.pdf
+    // http://educypedia.karadimov.info/library/DitherExplained.pdf
     // and the discussion around https://www.hydrogenaud.io/forums/index.php?showtopic=16963&st=25
 
     // I think, for a 32 --> 16 bits, the range of
     // random numbers needs to be from -2^16 to 2^16, i.e. from -65536 to 65536 inclusive, not from
     // -32768 to +32767
+    
+    // Actually, what would be generated here is from -65535 to 65535, i.e. one less on the limits.
 
     // See the original paper at
     // http://www.ece.rochester.edu/courses/ECE472/resources/Papers/Lipshitz_1992.pdf
@@ -666,23 +668,23 @@ static inline void process_sample(int32_t sample, char **outp, enum sps_format_t
     case SPS_FORMAT_S32:
     case SPS_FORMAT_S32_LE:
     case SPS_FORMAT_S32_BE:
-      dither_mask = (int64_t)1 << (64 + 1 - 32);
+      dither_mask = (int64_t)1 << (64 - 32);
       break;
     case SPS_FORMAT_S24:
     case SPS_FORMAT_S24_LE:
     case SPS_FORMAT_S24_BE:
     case SPS_FORMAT_S24_3LE:
     case SPS_FORMAT_S24_3BE:
-      dither_mask = (int64_t)1 << (64 + 1 - 24);
+      dither_mask = (int64_t)1 << (64 - 24);
       break;
     case SPS_FORMAT_S16:
     case SPS_FORMAT_S16_LE:
     case SPS_FORMAT_S16_BE:
-      dither_mask = (int64_t)1 << (64 + 1 - 16);
+      dither_mask = (int64_t)1 << (64 - 16);
       break;
     case SPS_FORMAT_S8:
     case SPS_FORMAT_U8:
-      dither_mask = (int64_t)1 << (64 + 1 - 8);
+      dither_mask = (int64_t)1 << (64 - 8);
       break;
     case SPS_FORMAT_UNKNOWN:
       die("Unexpected SPS_FORMAT_UNKNOWN while calculating dither mask.");
@@ -1673,10 +1675,15 @@ void *player_thread_func(void *arg) {
   case SPS_FORMAT_S24_3BE:
     conn->output_bytes_per_frame = 6;
     break;
+  
   case SPS_FORMAT_S24:
+  case SPS_FORMAT_S24_LE:
+  case SPS_FORMAT_S24_BE:
     conn->output_bytes_per_frame = 8;
     break;
   case SPS_FORMAT_S32:
+  case SPS_FORMAT_S32_LE:
+  case SPS_FORMAT_S32_BE:
     conn->output_bytes_per_frame = 8;
     break;
   default:
diff --git a/scripts/shairport-sync.conf b/scripts/shairport-sync.conf
index 7b030d6..a17d633 100644
--- a/scripts/shairport-sync.conf
+++ b/scripts/shairport-sync.conf
@@ -31,7 +31,7 @@ general =
 //	volume_control_profile = "standard" ; // use this advanced setting to specify how the airplay volume is transferred to the mixer volume.
 //		"standard" makes the volume change more quickly at lower volumes and slower at higher volumes.
 //		"flat" makes the volume change at the same rate at all volumes.
-//	volume_range_combined_hardware_priority = "no"; // when extending the volume range by combining the built-in software attenuator with the hardware mixer attenuator, set this to "yes" to reduce volume by using the hardware mixer first, then the built-in software attenuator. 
+//	volume_range_combined_hardware_priority = "no"; // when extending the volume range by combining the built-in software attenuator with the hardware mixer attenuator, set this to "yes" to reduce volume by using the hardware mixer first, then the built-in software attenuator.
 //	run_this_when_volume_is_set = "/full/path/to/application/and/args"; //	Run the specified application whenever the volume control is set or changed.
 //		The desired AirPlay volume is appended to the end of the command line – leave a space if you want it treated as an extra argument.
 //		AirPlay volume goes from 0 to -30 and -144 means "mute".
@@ -84,7 +84,7 @@ alsa =
 //	mixer_control_name = "PCM"; // the name of the mixer to use to adjust output volume. If not specified, volume in adjusted in software.
 //	mixer_device = "default"; // the mixer_device default is whatever the output_device is. Normally you wouldn't have to use this.
 //	output_rate = "auto"; // can be "auto", 44100, 88200, 176400 or 352800, but the device must have the capability.
-//	output_format = "auto"; // can be "auto", ""U8", "S8", "S16", "S16_LE", "S16_BE", "S24", "S24_LE", "S24_BE", "S24_3LE", "S24_3BE", "S32", "S32_LE" or "S32_BE" but the device must have the capability. Except where stated using (*LE or *BE), endianness matches that of the processor.
+//	output_format = "auto"; // can be "auto", "U8", "S8", "S16", "S16_LE", "S16_BE", "S24", "S24_LE", "S24_BE", "S24_3LE", "S24_3BE", "S32", "S32_LE" or "S32_BE" but the device must have the capability. Except where stated using (*LE or *BE), endianness matches that of the processor.
 //	disable_synchronization = "no"; // Set to "yes" to disable synchronization. Default is "no".
 //	period_size = <number>; // Use this optional advanced setting to set the alsa period size near to this value
 //	buffer_size = <number>; // Use this optional advanced setting to set the alsa buffer size near to this value
@@ -199,9 +199,9 @@ mqtt =
 {
 //	enabled = "no"; // set this to yes to enable the mqtt-metadata-service
 //	hostname = "iot.eclipse.org"; // Hostname of the MQTT Broker
-//	port = "1883";
-//	username = NULL; //set this to a string with your username, to enable username authentication
-//	password = NULL; //set this to a string with your password, to enable username & password authentication
+//	port = 1883; // Port on the MQTT Broker to connect to
+//	username = NULL; //set this to a string to your username in order to enable username authentication
+//	password = NULL; //set this to a string you your password in order to enable username & password authentication
 //	capath = NULL; //set this to the folder with the CA-Certificates to be accepted for the server certificate. If not set, TLS is not used
 //	cafile = NULL; //this may be used as an (exclusive) alternative to capath with a single file for all ca-certificates
 //	certfile = NULL; //set this to a string to a user certificate to enable MQTT Client certificates. keyfile must also be set!
@@ -216,7 +216,7 @@ mqtt =
 //	Available commands are "command", "beginff", "beginrew", "mutetoggle", "nextitem", "previtem", "pause", "playpause", "play", "stop", "playresume", "shuffle_songs", "volumedown", "volumeup"
 }
 
-// Diagnostic settings. These are for diagnostic and debugging only. Normally you sould leave them commented out
+// Diagnostic settings. These are for diagnostic and debugging only. Normally you should leave them commented out
 diagnostics =
 {
 //	disable_resend_requests = "no"; // set this to yes to stop Shairport Sync from requesting the retransmission of missing packets. Default is "no".
diff --git a/shairport.c b/shairport.c
index 9e9400b..667a565 100644
--- a/shairport.c
+++ b/shairport.c
@@ -992,7 +992,6 @@ int parse_options(int argc, char **argv) {
 #endif
 
 #ifdef CONFIG_MQTT
-    int tmpval = 0;
     config_set_lookup_bool(config.cfg, "mqtt.enabled", &config.mqtt_enabled);
     if (config.mqtt_enabled && !config.metadata_enabled) {
       die("You need to have metadata enabled in order to use mqtt");
@@ -1001,11 +1000,13 @@ int parse_options(int argc, char **argv) {
       config.mqtt_hostname = (char *)str;
       // TODO: Document that, if this is false, whole mqtt func is disabled
     }
-    if (config_lookup_int(config.cfg, "mqtt.port", &tmpval)) {
-      config.mqtt_port = tmpval;
-    } else {
-      // TODO: Is this the correct way to set a default value?
-      config.mqtt_port = 1883;
+    config.mqtt_port = 1883;
+    if (config_lookup_int(config.cfg, "mqtt.port", &value)) {
+      if ((value < 0) || (value > 65535))
+          die("Invalid mqtt port number  \"%sd\". It should be between 0 and 65535, default is 1883",
+              value);
+      else
+          config.mqtt_port = value;
     }
 
     if (config_lookup_string(config.cfg, "mqtt.username", &str)) {