Initial commit

Author: Ken Rossato

Makefile

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+TARGET = chiptune
+
+MCU   = atmega328p
+F_CPU = 16000000UL
+BAUD  = 31250UL
+
+CC      = avr-gcc
+OBJCOPY = avr-objcopy
+AVRSIZE = avr-size
+AVRDUDE = avrdude
+
+AVRDUDE_FLAGS = -C avrisp -P /dev/ttyACM0 -b 19200
+
+CSOURCES=$(wildcard *.c)
+SSOURCES=$(wildcard *.S)
+SOURCES=$(CSOURCES) $(SSOURCES)
+OBJECTS=$(CSOURCES:.c=.o) $(SSOURCES:.S=.o)
+HEADERS=$(wildcard *.h)
+
+NOISE_SHIFT_REGISTERS = -ffixed-r2 -ffixed-r3
+
+CPPFLAGS = -DF_CPU=$(F_CPU) -DBAUD=$(BAUD) -I.
+
+CFLAGS  = -O2 -std=gnu99 -Wall -Wimplicit-function-declaration
+CFLAGS += -funsigned-char -funsigned-bitfields -fpack-struct -fshort-enums 
+CFLAGS += -ffunction-sections -fdata-sections
+CFLAGS += $(NOISE_SHIFT_REGISTERS)
+
+LDFLAGS  = -Wl,-Map,$(TARGET).map 
+LDFLAGS += -Wl,--gc-sections 
+
+ARCH = -mmcu=$(MCU)
+
+%.o: %.c $(HEADERS) Makefile
+	$(CC) $(CFLAGS) $(CPPFLAGS) $(ARCH) -c -o $@ $<
+
+.S.o: $(HEADERS) Makefile
+	$(CC) $(CPPFLAGS) $(ARCH) -c -o $@ $<;
+
+$(TARGET).elf: $(OBJECTS)
+	$(CC) $(LDFLAGS) $(ARCH) $^ -o $@
+
+%.hex: %.elf
+	$(OBJCOPY) -j .text -j .data -O ihex $< $@
+
+.PHONY: all size clean flash
+
+all: $(TARGET).hex
+
+size: $(TARGET).elf
+	$(AVRSIZE) -C --mcu=$(MCU) $(TARGET).elf
+
+clean:
+	rm -f *.elf *.hex *.o
+
+flash: $(TARGET).hex
+	$(AVRDUDE) -p $(MCU) $(AVRDUDE_FLAGS) -U flash:w:$<

README.md

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+Arduino chiptune synthesizer
+============================
+
+This is my 8-bit synthesizer project for the Arduino UNO.  It'll probably work with minimal modification on any 8-bit AVR with at least 2k of RAM at 16MHz.  I compile with avr-gcc and upload with a SPI programmer, but it doesn't take up a ton of flash space so you should in theory be able to keep Optiboot if you tweak the makefile.
+
+Features:
+*  8 simultaneous independent channels at 44.1kHz
+*  Input over MIDI and 7x8 key matrix with separate assignable voices
+*  Square wave, triangle wave, and noise
+*  Square wave duty cycle adjustable to 50%, 25%, or 12.5%
+*  Attack-decay-sustain envelopes
+*  Vibrato, arpeggio, and echo effects
+*  Preprogrammed percussion using sliding pitches and shaped noise
+*  "Burst note" setting that plays hi-hat with notes
+*  8-beat record and playback (work in progress)
+
+This project is inspired by Linus Åkesson's incredible [Chipophone](http://linusakesson.net/chipophone/index.php).  My source code is written from scratch and is hopefully a little more reusable (I aim for MIDI and Arduino compatibility).  It uses the same MCP49x1 DAC for output and can be wired up with a few external components:
+
+For the audio output:
+
+*  MCP4921 DAC (can substitute 4911 or 4901)
+*  470uF electrolytic capacitor to block DC on the output
+*  100nF electorlytic capacitor to filter out noise on the volume knob
+*  10kOhm linear potentiometer to select the Vref level
+*  56kOhm volume limiting resistor
+*  Audio jack
+
+For MIDI input:
+
+*  6N138 optoisolator
+*  1N4148 diode
+*  220 and 470 ohm resistors
+*  MIDI socket
+
+For key-matrix input:
+
+*  74HC164 or 74HC595 shift register

constants.h

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+#ifndef CONSTANTS_H
+#define CONSTANTS_H
+
+#include <avr/io.h>
+
+#define NO_VALUE 255
+
+#define DRUM_MACHINE_1 252
+#define DRUM_MACHINE_2 253
+#define DRUM_HAT_NOTE 254
+#define TOTAL_NOTES 256
+
+#define NBANKS 3
+#define BANK_KEYS 0
+#define BANK_MIDI 1
+#define BANK_CPU  2
+
+#define MODE_BURST_BIT 0
+#define MODE_ARPEGGIO_BIT 1
+#define MODE_VIBRATO_BIT 2
+#define MODE_ECHO_BIT 3
+#define MODE_PEDAL_BIT 4
+
+#define MODE_NONE 0
+#define MODE_BURST    _BV(MODE_BURST_BIT)
+#define MODE_ARPEGGIO _BV(MODE_ARPEGGIO_BIT)
+#define MODE_VIBRATO  _BV(MODE_VIBRATO_BIT)
+#define MODE_ECHO     _BV(MODE_ECHO_BIT)
+#define MODE_PEDAL    _BV(MODE_PEDAL_BIT)
+
+#define NCHANNELS 8
+
+#define SHAPE_NOISE_BIT 0
+#define SHAPE_PCM_BIT 1
+#define SHAPE_SQUARE_BIT 2
+#define SHAPE_TRIANGLE_BIT 3
+#define SHAPE_DRUM_BIT 7
+
+#define SHAPE_NONE 0
+#define SHAPE_NOISE    _BV(SHAPE_NOISE_BIT)
+#define SHAPE_PCM      _BV(SHAPE_PCM_BIT)
+#define SHAPE_SQUARE   _BV(SHAPE_SQUARE_BIT)
+#define SHAPE_TRIANGLE _BV(SHAPE_TRIANGLE_BIT)
+#define SHAPE_DRUM     _BV(SHAPE_DRUM_BIT)
+
+#define DAC_BUF  6
+#define DAC_GA   5
+#define DAC_SHDN 4
+#define DAC_DEFAULT (_BV(DAC_GA) | _BV(DAC_SHDN))
+
+#define NINSTRUMENTS 4
+#define INSTRUMENT_DEFAULT 0
+#define INSTRUMENT_HAT 1
+#define INSTRUMENT_CYMBOL 2
+#define INSTRUMENT_SNARE 3
+
+#endif

drum.c

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+/* drum.c -
+     Drum definitions and playback queue
+
+   (c) 2016 Ken Rossato
+ */
+
+#include "main.h"
+#include "drum.h"
+
+uint8_t drum_machine_page = 0;
+const struct drum_t *drum_machine[2] = {&drums[0], &drums[0]};
+
+const struct drum_t drums[NDRUMS] = {
+    [DRUM_HAT] = {
+        .freq = 0xFFFF,
+        .slide = 0,
+        .shape = SHAPE_NOISE,
+        .instrument = &instruments[INSTRUMENT_HAT],
+        .duration = 5
+    },
+    [DRUM_TOM_HI] = {
+        .freq = 0x030A, // C4
+        .slide = -0x30,
+        .shape = SHAPE_TRIANGLE,
+        .instrument = &instruments[INSTRUMENT_DEFAULT],
+        .duration = 8,
+    },
+    [DRUM_TOM] = {
+        .freq = 0x028E, // A3
+        .slide = -0x30,
+        .shape = SHAPE_TRIANGLE,
+        .instrument = &instruments[INSTRUMENT_DEFAULT],
+        .duration = 8,
+    },
+    [DRUM_TOM_LO] = {
+        .freq = 0x0247, // G3
+        .slide = -0x30,
+        .shape = SHAPE_TRIANGLE,
+        .instrument = &instruments[INSTRUMENT_DEFAULT],
+        .duration = 8,
+    },
+    [DRUM_CYMBOL] = {
+        .freq = 0x8000,
+        .slide = 0,
+        .shape = SHAPE_NOISE,
+        .instrument = &instruments[INSTRUMENT_CYMBOL],
+        .duration = 15
+    },
+    [DRUM_SNARE_NOISE] = {
+        .freq = 0x1800,
+        .slide = 0x1733,
+        .shape = SHAPE_NOISE,
+        .instrument = &instruments[INSTRUMENT_SNARE],
+        .duration = 15
+    },
+    [DRUM_SNARE_TONE] = {
+        .freq = 0x030A, // C4
+        .slide = -0x20,
+        .shape = SHAPE_TRIANGLE,
+        .instrument = &instruments[INSTRUMENT_DEFAULT],
+        .duration = 15
+    },
+    [DRUM_SNARE_LO_TONE] = {
+        .freq = 0x0269, // G#3
+        .slide = -0x14,
+        .shape = SHAPE_TRIANGLE,
+        .instrument = &instruments[INSTRUMENT_DEFAULT],
+        .duration = 15
+    },
+    [DRUM_KICK] = {
+        .freq = 0x15B, // A#2
+        .slide = -0x10,
+        .shape = SHAPE_TRIANGLE,
+        .instrument = &instruments[INSTRUMENT_DEFAULT],
+        .duration = 15
+    },
+    [DRUM_KICK_SQUARE] = {
+        .freq = 0x15B,
+        .slide = -0x10,
+        .shape = SHAPE_SQUARE,
+        .instrument = &instruments[INSTRUMENT_CYMBOL],
+        .duration = 15
+    }
+};
+
+uint8_t allocate_drum_note(uint8_t drum) {
+    drum_machine_page = (drum_machine_page + 1) & 2;
+    drum_machine[drum_machine_page] = &drums[drum];
+    return DRUM_MACHINE_1 + drum_machine_page;
+}

drum.h

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+/* drum.h -
+     Drum definitions and playback queue
+
+   (c) 2016 Ken Rossato
+ */
+
+#ifndef DRUM_H
+#define DRUM_H
+
+#include "main.h"
+
+#define DRUM_HAT 0
+#define DRUM_TOM_HI 1
+#define DRUM_TOM 2
+#define DRUM_TOM_LO 3
+#define DRUM_CYMBOL 4
+#define DRUM_SNARE_NOISE 5
+#define DRUM_SNARE_TONE 6
+#define DRUM_SNARE_LO_TONE 7
+#define DRUM_KICK 8
+#define DRUM_KICK_SQUARE 9
+#define NDRUMS 10
+
+struct drum_t {
+    uint16_t freq;
+    int16_t slide;
+    uint8_t shape;
+    const struct instrument_t *instrument;
+    uint8_t duration;
+};
+extern const struct drum_t drums[];
+extern const struct drum_t *drum_machine[];
+
+uint8_t allocate_drum_note(uint8_t drum);
+
+#endif