initial implementation of pitch bending

gen_pitch_table.py

@@ -52,4 +52,16 @@ for i in range(start_pitch, end_pitch):
         period = int(period / 2)
     print("    " + str(period) + "ul,\t// " + name)
 
+print("};")
+
+print("")
+print("// scale factors for bend values from 0 to 255")
+print("// We don't support the full 16385 levels of MIDI bend")
+print("// MIDI bend values have to be converted first to the nearest supported one")
+print("constexpr float midi_pitch_bend_scale[256] = {")
+
+for i in range(0, 256):
+    factor = pow(2, (8192 - i * 64) / 49152)
+    print("    " + str(factor) + "f,\t// " + str(i))
+
 print("};")

main.cpp

@@ -53,6 +53,11 @@ void midi_note_off(uint8_t channel, uint8_t note, uint8_t velocity) {
     motors[channel - 1].TickOff();
 }
 
+void midi_pitch_bend(uint8_t channel, int bend) {
+    ASSERT_CHANNEL();
+    motors[channel - 1].TickPitchBend(bend);
+}
+
 int main() {
     // Arduino library initialization
     // Needed for some functions to work (like micros)
@@ -76,6 +81,7 @@ int main() {
     // Set up MIDI callbacks
     MIDI.setHandleNoteOn(midi_note_on);
     MIDI.setHandleNoteOff(midi_note_off);
+    MIDI.setHandlePitchBend(midi_pitch_bend);
 
     unsigned long cur_micros;
     unsigned long cur_half_micros;

motor_control.cpp

@@ -4,7 +4,8 @@
 
 MotorControl::MotorControl(int pin_dir, int pin_step) :
     pin_dir(pin_dir), pin_step(pin_step),
-    last_tick_half_micros(0), tick_period_half_micros(0)
+    last_tick_half_micros(0), tick_period_half_micros(0),
+    tick_period_orig_half_micros(0)
 {
     // No actual constructor logic -- initialization is in Init()
 }
@@ -19,6 +20,7 @@ void MotorControl::Init() {
 
 void MotorControl::TickOn(unsigned long period_half_micros) {
     tick_period_half_micros = period_half_micros;
+    tick_period_orig_half_micros = period_half_micros;
     // Force the next tick to happen
     last_tick_half_micros = 0;
 }
@@ -32,8 +34,19 @@ void MotorControl::TickAtPitch(unsigned int midi_pitch) {
     TickOn(midi_pitch_period[midi_pitch - midi_pitch_offset]);
 }
 
+void MotorControl::TickPitchBend(int bend) {
+    if (bend < 0 || bend >= 16384) return;
+    if (tick_period_orig_half_micros == 0) return;
+
+    // Scale the MIDI bend value down to 0 - 255
+    bend = bend / 64;
+
+    tick_period_half_micros = (unsigned long) (((float) tick_period_orig_half_micros) * midi_pitch_bend_scale[bend]);
+}
+
 void MotorControl::TickOff() {
     tick_period_half_micros = 0;
+    tick_period_orig_half_micros = 0;
 }
 
 void MotorControl::Tick(unsigned long cur_half_micros) {

motor_control.h

@@ -8,6 +8,8 @@ class MotorControl {
         unsigned long last_tick_half_micros;
         // Interval of motor ticking; 0 to disable the motor
         unsigned long tick_period_half_micros;
+        // Original period of motor ticking (without applying bend)
+        unsigned long tick_period_orig_half_micros;
 
         void DoTick();
     public:
@@ -19,6 +21,8 @@ class MotorControl {
         void TickOn(unsigned long period_half_micros);
         // Set the motor to tick with a given MIDI pitch
         void TickAtPitch(unsigned int midi_pitch);
+        // Set the pitch bend
+        void TickPitchBend(int bend);
         // Turn off the motor
         void TickOff();
         // Perform a tick if necessary