From 698c7895141f412be565949f33f33f62e835a74e Mon Sep 17 00:00:00 2001
From: midilab <contact@midilab.co>
Date: Fri, 9 Mar 2018 10:15:46 -0300
Subject: [PATCH] Roland TB303 main engine added as example for a step
 sequencer using uClock

---
 README.md | 176 +++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 173 insertions(+), 3 deletions(-)

diff --git a/README.md b/README.md
index 75d0f1e..cf283a1 100755
--- a/README.md
+++ b/README.md
@@ -75,11 +75,181 @@ void loop() {
 }
 ```
 
-### A Simple Step Sequencer
-A simple step sequencer for MIDI devices:
+### Acid Step Sequencer
+A clone of Roland TB303 step sequencer main engine, the schematics for user interface are avaliable on example folder.
 
 
 ```c++
-Soon...
+// Roland TB303 Step Sequencer engine clone.
+// No interface here, just the engine as example.
+#include "Arduino.h"
+#include <uClock.h>
+
+// Sequencer config
+#define STEP_MAX_SIZE      16
+#define NOTE_LENGTH        4 // min: 1 max: 5 DO NOT EDIT BEYOND!!!
+#define NOTE_VELOCITY      90
+#define ACCENT_VELOCITY    127
+
+// MIDI modes
+#define MIDI_CHANNEL      0 // 0 = channel 1
+
+// Sequencer data
+typedef struct
+{
+  uint8_t note;
+  bool accent;
+  bool glide;
+  bool rest;
+} SEQUENCER_STEP_DATA;
+
+SEQUENCER_STEP_DATA _sequencer[STEP_MAX_SIZE];
+
+typedef struct
+{
+  uint8_t note;
+  int8_t length;
+} STACK_NOTE_DATA;
+
+STACK_NOTE_DATA _note_stack[2];
+
+bool _playing = false;
+uint16_t _step = 0;
+uint16_t _step_length = STEP_MAX_SIZE;
+
+// MIDI clock, start, stop, note on and note off byte definitions - based on MIDI 1.0 Standards.
+#define MIDI_CLOCK 0xF8
+#define MIDI_START 0xFA
+#define MIDI_STOP  0xFC
+#define NOTE_ON    0x90
+#define NOTE_OFF   0x80
+
+void sendMidiMessage(uint8_t command, uint8_t byte1, uint8_t byte2)
+{ 
+  // send midi message
+  command = command | (uint8_t)MIDI_CHANNEL;
+  Serial.write(command);
+  Serial.write(byte1);
+  Serial.write(byte2);
+}
+
+// The callback function wich will be called by uClock each Pulse of 16PPQN clock resolution.
+// Each call represents exactly one step here.
+void ClockOut16PPQN(uint32_t * tick) 
+{
+  uint16_t step;
+  bool glide_ahead;
+  
+  // get actual step.
+  _step = *tick % _step_length;
+  
+  // send note on only if this step are not in rest mode
+  if ( _sequencer[_step].rest == false ) {
+    sendMidiMessage(NOTE_ON, _sequencer[_step].note, _sequencer[_step].accent ? ACCENT_VELOCITY : NOTE_VELOCITY);
+    // do we have a glide ahead us?
+    step = _step;
+    for ( uint16_t i = 1; i < _step_length; i++  ) {
+      ++step;
+      step = step % _step_length;
+      if ( _sequencer[step].glide == true && _sequencer[step].rest == false ) {
+        _note_stack[1].note = _sequencer[_step].note;
+        _note_stack[1].length = NOTE_LENGTH + (i * 6);
+        glide_ahead = true;
+        break;
+      } else if ( _sequencer[step].rest == false ) {
+        glide_ahead = false;
+        break;
+      }
+    }
+    if ( glide_ahead == false ) {
+      _note_stack[0].note = _sequencer[_step].note;
+      _note_stack[0].length = NOTE_LENGTH;
+    }
+  }  
+}
+
+// The callback function wich will be called by uClock each Pulse of 96PPQN clock resolution.
+void ClockOut96PPQN(uint32_t * tick) 
+{
+  // Send MIDI_CLOCK to external hardware
+  Serial.write(MIDI_CLOCK);
+
+  // handle note on stack
+  // [1] is notes to be glided, its in hold on mode until we reach the glided step
+  if ( _note_stack[1].length != -1 ) {
+    --_note_stack[1].length;
+    if ( _note_stack[1].length == 0 ) {
+      sendMidiMessage(NOTE_OFF, _note_stack[1].note, 0);
+      _note_stack[1].length = -1;
+    }
+  }  
+  // [0] is the actual step note stack
+  if ( _note_stack[0].length != -1 ) {
+    --_note_stack[0].length;
+    if ( _note_stack[0].length == 0 ) {
+      sendMidiMessage(NOTE_OFF, _note_stack[0].note, 0);
+      _note_stack[0].length = -1;
+    }
+  }
+}
+
+// The callback function wich will be called when clock starts by using Clock.start() method.
+void onClockStart() 
+{
+  Serial.write(MIDI_START);
+}
+
+// The callback function wich will be called when clock stops by using Clock.stop() method.
+void onClockStop() 
+{
+  Serial.write(MIDI_STOP);
+  sendMidiMessage(NOTE_OFF, _note_stack[1].note, 0);
+  sendMidiMessage(NOTE_OFF, _note_stack[0].note, 0);
+}
+
+void setup() 
+{
+  // Initialize serial communication
+  // the default MIDI serial speed communication at 31250 bits per second
+  Serial.begin(31250); 
+
+  // Inits the clock
+  uClock.init();
+  
+  // Set the callback function for the clock output to send MIDI Sync message.
+  uClock.setClock96PPQNOutput(ClockOut96PPQN);
+  
+  // Set the callback function for the step sequencer on 16ppqn
+  uClock.setClock16PPQNOutput(ClockOut16PPQN);  
+  
+  // Set the callback function for MIDI Start and Stop messages.
+  uClock.setOnClockStartOutput(onClockStart);  
+  uClock.setOnClockStopOutput(onClockStop);
+  
+  // Set the clock BPM to 126 BPM
+  uClock.setTempo(126);
+
+  // initing sequencer data
+  for ( uint16_t i = 0; i < STEP_MAX_SIZE; i++ ) {
+    _sequencer[i].note = 36;
+    _sequencer[i].accent = false;
+    _sequencer[i].glide = false;
+    _sequencer[i].rest = false;
+  }
+  
+  // starts the sequencer
+  uClock.start();
+
+  // pins, buttons, leds and pots config
+  //configureYourUserInterface();
+}
+
+// User interaction goes here
+void loop() 
+{
+  //processYourButtons();
+  //processYourLeds();
+  //processYourPots();
+}
 ```