Make the incomplete MIDIToneGenerator project work with up to three notes, using a LRU (Least Recently Used) algorithm to discard the oldest set note when the note table becomes full.

2 files changed, 61 insertions, 27 deletions

diff --git a/Projects/Incomplete/MIDIToneGenerator/MIDIToneGenerator.c b/Projects/Incomplete/MIDIToneGenerator/MIDIToneGenerator.c
index 7c5fc9a62..c8e06bed4 100644
--- a/Projects/Incomplete/MIDIToneGenerator/MIDIToneGenerator.c
+++ b/Projects/Incomplete/MIDIToneGenerator/MIDIToneGenerator.c
@@ -78,14 +78,7 @@ const uint8_t SineTable[256] =
 };

 

 /** Array of structures describing each note being generated */

-struct

-{

-	uint8_t  Pitch;

-	uint32_t TableIncrement;

-	uint32_t TablePosition;

-} NoteData[3];

-

-uint8_t PhaseCounter;

+DDSNoteData NoteData[MAX_SIMULTANEOUS_NOTES];

 

 /** Main program entry point. This routine contains the overall program flow, including initial

  *  setup of all components and the main program loop.

@@ -104,19 +97,34 @@ int main(void)
 		{

 			if ((ReceivedMIDIEvent.Command == (MIDI_COMMAND_NOTE_ON >> 4)) && ((ReceivedMIDIEvent.Data1 & 0x0F) == 0))

 			{

+				DDSNoteData* LRUNoteStruct = &NoteData[0];

+			

 				/* Find a free entry in the note table to use for the note being turned on */

 				for (uint8_t i = 0; i < MAX_SIMULTANEOUS_NOTES; i++)

 				{

+					/* Check if the note is unused */

 					if (!(NoteData[i].Pitch))

 					{

-						NoteData[i].Pitch          = ReceivedMIDIEvent.Data2;

-						NoteData[i].TableIncrement = (uint32_t)(BASE_INCREMENT * SCALE_FACTOR) +

-						                             ((uint32_t)(BASE_INCREMENT * NOTE_OCTIVE_RATIO * SCALE_FACTOR) *

-						                              (ReceivedMIDIEvent.Data2 - BASE_PITCH_INDEX));

-						NoteData[i].TablePosition  = 0;

+						/* If a note is unused, it's age is essentially infinite - always prefer unused not entries */

+						LRUNoteStruct = &NoteData[i];

 						break;

 					}

+					else if (NoteData[i].LRUAge > LRUNoteStruct->LRUAge)

+					{

+						/* If an older entry that the current entry has been found, prefer overwriting that one */						

+						LRUNoteStruct = &NoteData[i];

+					}

+					

+					NoteData[i].LRUAge++;

 				}

+				

+				/* Update the oldest note entry with the new note data and reset its age */

+				LRUNoteStruct->Pitch          = ReceivedMIDIEvent.Data2;

+				LRUNoteStruct->TableIncrement = (uint32_t)(BASE_INCREMENT * SCALE_FACTOR) +

+						                         ((uint32_t)(BASE_INCREMENT * NOTE_OCTIVE_RATIO * SCALE_FACTOR) *

+						                          (ReceivedMIDIEvent.Data2 - BASE_PITCH_INDEX));

+				LRUNoteStruct->TablePosition  = 0;

+				LRUNoteStruct->LRUAge         = 0;

 

 				/* Turn on indicator LED to indicate note generation activity */

 				LEDs_SetAllLEDs(LEDS_LED1);

@@ -129,11 +137,9 @@ int main(void)
 				for (uint8_t i = 0; i < MAX_SIMULTANEOUS_NOTES; i++)

 				{

 					if (NoteData[i].Pitch == ReceivedMIDIEvent.Data2)

-					{

-						NoteData[i].Pitch = 0;

-						FoundActiveNote      = true;

-						break;

-					}

+					  NoteData[i].Pitch = 0;

+					else if (NoteData[i].Pitch)

+					  FoundActiveNote   = true;

 				}

 				

 				/* If all notes off, turn off the indicator LED */

@@ -182,15 +188,15 @@ void SetupHardware(void)
 

 	/* Sample reload timer initialization */

 	TIMSK0  = (1 << OCIE0A);

-	OCR0A   = 255;

+	OCR0A   = (VIRTUAL_SAMPLE_TABLE_SIZE / 8);

 	TCCR0A  = (1 << WGM01);  // CTC mode

-	TCCR0B  = (1 << CS00);   // Fcpu speed

+	TCCR0B  = (1 << CS01);   // Fcpu/8 speed

 

 	/* Set speaker as output */

 	DDRC |= (1 << 6);

 

 	/* PWM speaker timer initialization */

-	TCCR3A  = ((1 << WGM30) | (1 << COM3A1) | (1 << COM3A0)); // Set on match, clear on TOP

+	TCCR3A  = ((1 << WGM31) | (1 << COM3A1) | (1 << COM3A0)); // Set on match, clear on TOP

 	TCCR3B  = ((1 << WGM32) | (1 << CS30));  // Fast 8-Bit PWM, Fcpu speed

 }

 

@@ -208,6 +214,10 @@ void EVENT_USB_Device_Disconnect(void)
 {

 	LEDs_SetAllLEDs(LEDMASK_USB_NOTREADY);

 

+	/* Disable any notes currently being played */

+	for (uint8_t i = 0; i < MAX_SIMULTANEOUS_NOTES; i++)

+	  NoteData[i].Pitch = 0;

+

 	/* Set speaker as input to reduce current draw */

 	DDRC &= ~(1 << 6);

 }

diff --git a/Projects/Incomplete/MIDIToneGenerator/MIDIToneGenerator.h b/Projects/Incomplete/MIDIToneGenerator/MIDIToneGenerator.h
index c0644374a..2936ca2c7 100644
--- a/Projects/Incomplete/MIDIToneGenerator/MIDIToneGenerator.h
+++ b/Projects/Incomplete/MIDIToneGenerator/MIDIToneGenerator.h
@@ -65,14 +65,38 @@
 		/** LED mask for the library LED driver, to indicate that an error has occurred in the USB interface. */

 		#define LEDMASK_USB_ERROR        (LEDS_LED1 | LEDS_LED3)

 		

-		#define SCALE_FACTOR             65536

-		#define BASE_FREQUENCY           27.5

-		#define NOTE_OCTIVE_RATIO        1.05946

-		#define BASE_PITCH_INDEX         21

-		#define MAX_SIMULTANEOUS_NOTES   3

+		/** Scale factor used to convert the floating point frequencies and ratios into a fixed point number */

+		#define SCALE_FACTOR               65536

 		

-		#define BASE_INCREMENT           (((F_CPU / 255 / 2) / BASE_FREQUENCY))

+		/** Base (lowest) allowable MIDI note frequency */

+		#define BASE_FREQUENCY             27.5

 		

+		/** Ratio between each note in an octave */

+		#define NOTE_OCTIVE_RATIO          1.05946

+		

+		/** Lowest valid MIDI pitch index */

+		#define BASE_PITCH_INDEX           21

+		

+		/** Maximum number of MIDI notes that can be played simultaneously */

+		#define MAX_SIMULTANEOUS_NOTES     3

+		

+		/** Number of samples in the virtual sample table (can be expanded to lower maximum frequency, but allow for

+		 *  more simultaneous notes due to the reduced amount of processing time needed when the samples are spaced out)

+		 */

+		#define VIRTUAL_SAMPLE_TABLE_SIZE  512

+		

+		/** Sample table increments per period for the base MIDI note frequency */

+		#define BASE_INCREMENT             (((F_CPU / VIRTUAL_SAMPLE_TABLE_SIZE / 2) / BASE_FREQUENCY))

+

+	/* Type Defines: */

+		typedef struct

+		{

+			uint8_t  LRUAge;

+			uint8_t  Pitch;

+			uint32_t TableIncrement;

+			uint32_t TablePosition;

+		} DDSNoteData;		

+

 	/* Function Prototypes: */

 		void SetupHardware(void);