added clock decimal precision(128.5bpm). added a buffer for average i…

…nterval tick reading on getTempo() to smooth slave tempo retrive. Revised Teensy USB midi clock monitor

examples/TeensyUsbSlaveMidiClockMonitor/TeensyUsbSlaveMidiClockMonitor.ino

@@ -4,15 +4,21 @@
  * MIDI hid compilant slave clock box with 
  * monitor support using oled displays
  *
- * Making use of a 250 usceconds timer to
+ * Making use of a 16 usceconds timer to
  * handle MIDI input to avoid jitter on clock
  * 
  * You need the following libraries to make it work
  * - u8g2
  * - uClock
+ *
+ * This example make use of drift values (1, 4) 
+ * respectively for internal and external drift reference.
+ * This example was tested on a macbook 
+ * running ableton live 9 as master clock
+ *
  * This example code is in the public domain.
  */
-
+ 
 #include <U8x8lib.h>
 
 //
@@ -28,8 +34,8 @@ IntervalTimer teensyTimer;
 #define MIDI_START 0xFA
 #define MIDI_STOP  0xFC
 
-char bpm_str[3];
-uint16_t bpm = 126;
+char bpm_str[4];
+float bpm = 126;
 uint8_t bpm_blink_timer = 1;
 uint8_t clock_state = 1;
 
@@ -60,6 +66,7 @@ void onClockStart() {
 
 void onClockStop() {
   usbMIDI.sendRealTime(MIDI_STOP);
+  digitalWrite(LED_BUILTIN, LOW);
 }
 
 // External clock handlers
@@ -105,28 +112,44 @@ void setup() {
   //
   // Setup our clock system
   // drift for USB Teensy
-  uClock.setDrift(1);
+  uClock.setDrift(1, 4);
   uClock.init();
   uClock.setClock96PPQNOutput(ClockOut96PPQN);
   // For MIDI Sync Start and Stop
   uClock.setOnClockStartOutput(onClockStart);
   uClock.setOnClockStopOutput(onClockStop);
   uClock.setMode(uClock.EXTERNAL_CLOCK);
-  // make use of 250us timer to handle midi input sync
-  teensyTimer.begin(handleMidiInput, 250); 
+  // make use of 16us timer to handle midi input sync
+  teensyTimer.begin(handleMidiInput, 16); 
+  teensyTimer.priority(80);
 }
 
 void handleMidiInput() {
   while (usbMIDI.read()) {
   }
 }
 
+void printBpm(float _bpm, uint8_t col, uint8_t line) {
+    int b = (int)_bpm;
+    int c = (int)((_bpm-b)*10);
+    itoa(b, bpm_str, 10);
+    if (b > 99) {
+      u8x8->drawUTF8(col, line, bpm_str);
+    } else {
+      bpm_str[2] = "\0";
+      u8x8->drawUTF8(col, line, " ");
+      u8x8->drawUTF8(col+1, line, bpm_str);
+    }
+    u8x8->drawUTF8(col+3, line, ".");
+    itoa(c, bpm_str, 10);
+    u8x8->drawUTF8(col+4, line, bpm_str);
+    u8x8->drawUTF8(col+5, line, "bpm"); 
+}
+
 void loop() {
   if (bpm != uClock.getTempo()) {
     bpm = uClock.getTempo();
-    itoa(bpm, bpm_str, 10);
-    u8x8->drawUTF8(10, 7, bpm_str);
-    u8x8->drawUTF8(13, 7, "bpm"); 
+    printBpm(bpm, 8, 7);
   }
   if (clock_state != uClock.state) { 
     clock_state = uClock.state;

library.properties

@@ -1,5 +1,5 @@
 name=uClock
-version=0.9.2
+version=0.9.4
 author=Romulo Silva <[email protected]>, Manuel Odendahl <[email protected]>
 maintainer=Romulo Silva <[email protected]>
 sentence=BPM clock generator for Arduino and Teensy boards

src/uClock.cpp

@@ -3,7 +3,7 @@
  *  Project     BPM clock generator for Arduino
  *  @brief      A Library to implement BPM clock tick calls using hardware timer1 interruption. Tested on ATmega168/328, ATmega16u4/32u4 and ATmega2560.
  *              Derived work from mididuino MidiClock class. (c) 2008 - 2011 - Manuel Odendahl - [email protected]
- *  @version    0.9.3
+ *  @version    0.9.4
  *  @author     Romulo Silva
  *  @date       08/21/2020
  *  @license    MIT - (c) 2020 - Romulo Silva - [email protected]
@@ -39,13 +39,14 @@ IntervalTimer _teensyTimer;
 void teensyInterrupt();
 void initTeensyTimer()
 {
-	_teensyTimer.begin(teensyInterrupt, 16); 
+	// 62500Hz
+	_teensyTimer.begin(teensyInterrupt, 16);
 	// Set the interrupt priority level, controlling which other interrupts
 	// this timer is allowed to interrupt. Lower numbers are higher priority, 
 	// with 0 the highest and 255 the lowest. Most other interrupts default to 128. 
 	// As a general guideline, interrupt routines that run longer should be given 
 	// lower priority (higher numerical values).
-	//_teensyTimer.priority(128);
+	_teensyTimer.priority(0);
 }
 #else
 void initArduinoTimer()
@@ -103,6 +104,7 @@ uClockClass::uClockClass()
 	// 1 is good on teensy lc usb midi
 	internal_drift = 11;
 	external_drift = 11;
+	tempo = 120;
 	pll_x = 220;
 	start_timer = 0;
 	last_interval = 0;
@@ -116,11 +118,13 @@ uClockClass::uClockClass()
 	onClock16PPQNCallback = NULL;
 	onClockStartCallback = NULL;
 	onClockStopCallback = NULL;
+
+	// first interval calculus
+	setTempo(tempo);
 }
 
 void uClockClass::init() 
 {
-	setTempo(120);
 	initWorkTimer();
 }
 
@@ -161,7 +165,7 @@ void uClockClass::pause()
 	}
 }
 
-void uClockClass::setTempo(uint16_t bpm) 
+void uClockClass::setTempo(float bpm) 
 {
 	if (mode == EXTERNAL_CLOCK) {
 		return;
@@ -177,20 +181,27 @@ void uClockClass::setTempo(uint16_t bpm)
 
 	tempo = bpm;
 
-	ATOMIC(	
+	ATOMIC(
+		interval = (uint16_t)((156250.0 / tempo) - internal_drift);
 		//interval = 62500 / (tempo * 24 / 60) - internal_drift;
-		interval = (uint16_t)(156250 / tempo) - internal_drift;
 	)
 }
 
-uint16_t uClockClass::getTempo() 
+float uClockClass::getTempo() 
 {
 	if (mode == EXTERNAL_CLOCK) {
-		uint16_t external_interval;
-		ATOMIC(
-			external_interval = interval;
-		)
-		tempo = (156250 / (external_interval + external_drift));
+		uint32_t acc = 0;
+		uint8_t acc_counter = 0;
+		for (uint8_t i=0; i < EXT_INTERVAL_BUFFER_SIZE; i++) {
+			if ( ext_interval_buffer[i] != 0) {
+				acc += ext_interval_buffer[i];
+				++acc_counter;
+			}
+		}
+		if (acc != 0) {
+			// get average interval, because MIDI sync world is a wild place...
+			tempo = (float)(156250.0 / ((acc / acc_counter) + external_drift));
+		}
 	}
 	return tempo;
 }
@@ -232,6 +243,8 @@ void uClockClass::resetCounters()
 	mod6_counter = 0;
 	indiv96th_counter = 0;
 	inmod6_counter = 0;
+	ext_interval_buffer[EXT_INTERVAL_BUFFER_SIZE] = {0};
+	ext_interval_idx = 0;
 }
 
 // TODO: Tap stuff
@@ -273,6 +286,9 @@ void uClockClass::handleExternalClock()
 			} else {
 				interval = (((uint32_t)interval * (uint32_t)pll_x) + (uint32_t)(256 - pll_x) * (uint32_t)last_interval) >> 8;
 			}
+			// accumulate interval incomming ticks data(for a better getTempo stability over bad clocks)
+			ext_interval_buffer[ext_interval_idx] = interval;
+			ext_interval_idx = ++ext_interval_idx % EXT_INTERVAL_BUFFER_SIZE;
 			break;
 	}
 }

src/uClock.h

@@ -3,7 +3,7 @@
  *  Project     BPM clock generator for Arduino
  *  @brief      A Library to implement BPM clock tick calls using hardware timer1 interruption. Tested on ATmega168/328, ATmega16u4/32u4 and ATmega2560.
  *              Derived work from mididuino MidiClock class. (c) 2008 - 2011 - Manuel Odendahl - [email protected]
- *  @version    0.9.3
+ *  @version    0.9.4
  *  @author     Romulo Silva
  *  @date       08/21/2020
  *  @license    MIT - (c) 2020 - Romulo Silva - [email protected]
@@ -35,6 +35,8 @@
 
 #define PHASE_FACTOR 16
 
+#define EXT_INTERVAL_BUFFER_SIZE 40
+
 #define SECS_PER_MIN  (60UL)
 #define SECS_PER_HOUR (3600UL)
 #define SECS_PER_DAY  (SECS_PER_HOUR * 24L)
@@ -47,11 +49,6 @@ enum {
 	STARTED
 } state;
 
-enum {
-	INTERNAL_CLOCK = 0,
-	EXTERNAL_CLOCK
-} mode;
-
 class uClockClass {
 
 	private:
@@ -67,7 +64,6 @@ class uClockClass {
 		volatile uint16_t interval;
 		volatile uint16_t last_clock;
 
-		uint8_t ppqn;
 		uint32_t div96th_counter;
 		uint32_t div32th_counter;
 		uint32_t div16th_counter;
@@ -77,13 +73,16 @@ class uClockClass {
 		uint16_t pll_x;
 		uint8_t internal_drift;
 		uint8_t external_drift;
-		uint16_t tempo;
+		float tempo;
 		uint32_t start_timer;
 		uint8_t mode;
 
 		uint16_t last_interval;
 		uint16_t sync_interval;
 
+		uint16_t ext_interval_buffer[EXT_INTERVAL_BUFFER_SIZE];
+		uint16_t ext_interval_idx;
+
 	public:
 
 		uint8_t INTERNAL_CLOCK = 0;
@@ -122,8 +121,8 @@ class uClockClass {
 		void start();
 		void stop();
 		void pause();
-		void setTempo(uint16_t bpm);
-		uint16_t getTempo();
+		void setTempo(float bpm);
+		float getTempo();
 		void setDrift(uint8_t internal, uint8_t external = 255);
 
 		// external timming control