add GPIO note gate functions to control synth VCA

Makefile

@@ -1,7 +1,7 @@
 
 CXX=g++
 CXXFLAGS= -std=c++11 -g -ggdb3 -Wall
-LDFLAGS=-lasound
+LDFLAGS=-lasound -lgpiod
 
 OBJDIR = build
 SRCDIR = src

src/main.cpp

@@ -1,5 +1,4 @@
 
-//	TODO: gate on/off controls, can just use hardware GPIO in digital mode
 //	TODO: update README with wiring instructions for SPI to DAC
 //	TODO: DAC voltage stepping
 //		if we use DAC input 4080 = 5V, then we can do steps of 1/12V on exactly
@@ -13,10 +12,13 @@
 #include <unistd.h>
 #include <linux/spi/spi.h>
 
-#include "spi.h"
+#include "spi.h" // FIXME: should rename to gpio.h
 #include "midi.h"
 
 
+#define GPIO_CHIP_NAME "gpiochip1"
+#define GPIO_LINE_NUM 82 // GPIO Pin #38 on 'le-potato'
+
 #define SPI_SPEED 1000000
 #define SPI_BUFFER_LENGTH 2
 #define SPI_CHANNEL 0
@@ -57,18 +59,49 @@ convertNoteToDACInput(u8 midi_note)
 }
 
 void
-loopMIDI(alsa_sequencer* seq, spi_connection* spi)
+loopMIDI(alsa_sequencer* seq, spi_connection* spi, gpio_info* gpio)
 {
+	// TODO: there's probably a more elegant way to handle this, but this was
+	// 	the first idea that came up, and seems to work
+	// NOTE: MIDI Note '0' is a vaild note, but 255 is not. So, we'll use 255
+	// 	as a placeholder to represent an unused PLAYING_NOTE
+	static const u32 MAX_NOTES = 6;
+	static u8 PLAYING_NOTES[MAX_NOTES] = {255,255,255,255,255,255};
+
 	while(1)
 	{
 		printf("\n--------------------\n");
 		snd_seq_event_t *ev = nullptr;
 		snd_seq_event_input(seq->seq_handle, &ev);
-		i32 note = midiProcess(ev);
 
-		if (note >= 0) {
-			i32 dac_in = convertNoteToDACInput(note);
+		// FIXME: we should only be processing notes from the first channel
+		alsa_note_event nev = midiProcess(ev);
+		bool note_tracked = false;
+
+		for (u32 i = 0; i < MAX_NOTES; i++) {
+			if (PLAYING_NOTES[i] == nev.note) {
+				note_tracked = true;
+
+				if (nev.note_on) { // do nothing
+					break;
+				} else { // remove note from tracked list
+					assert(gpioSetValue(gpio, 0)); // send set gate off
+					PLAYING_NOTES[i] = 255;
+					break;
+				}
+			}
+		}
 
+		// send note voltage to DAC, and add note to tracked list
+		if (!note_tracked && nev.note_on ) {
+			for (u32 i = 0; i < MAX_NOTES; i++) {
+				if (PLAYING_NOTES[i] == 255) {
+					PLAYING_NOTES[i] = nev.note;
+					assert(gpioSetValue(gpio, 1)); // send set gate on
+				}
+			}
+
+			i32 dac_in = convertNoteToDACInput(nev.note);
 			// TODO: could check return value here for SPI error
 			spiSendVoltage(spi, dac_in);
 		}
@@ -101,6 +134,11 @@ main(i32 argc, char* argv[])
 	u8 spi_buf[SPI_BUFFER_LENGTH] = {0};
 	spi_connection spi = spiInit(SPI_SPEED, MAX_DAC_INPUT, spi_buf, SPI_BUFFER_LENGTH, SPI_FLAGS, SPI_CHANNEL);
 
+	gpio_info gpio = {0};
+
+	if (!gpioInit(&gpio, GPIO_CHIP_NAME, GPIO_LINE_NUM))
+		return 1;
+
 	if (spi.fd < 0) {
 		printf("error opening SPI device\n");
 		return 1;
@@ -112,7 +150,7 @@ main(i32 argc, char* argv[])
 	while ((opt = getopt(argc, argv, "tlk:h")) != -1) {
 		switch (opt) {
 			case 'l':
-				loopMIDI(&seq, &spi);
+				loopMIDI(&seq, &spi, &gpio);
 				break;
 			case 'k':
 				if (!midiConnect(&seq, optarg)) {
@@ -120,7 +158,7 @@ main(i32 argc, char* argv[])
 					exit(1);
 				}
 
-				loopMIDI(&seq, &spi);
+				loopMIDI(&seq, &spi, &gpio);
 				break;
 			case 't':
 				loopTestVoltages(&spi);

src/midi.cpp

@@ -63,22 +63,27 @@ midiConnect(alsa_sequencer* seq, const char* midi_device)
 	return false;
 }
 
-i32
+alsa_note_event
 midiProcess(const snd_seq_event_t* ev)
 {
 	assert(ev != nullptr);
-	i32 note = -1;
+	alsa_note_event nev = {0};
 
 	if((ev->type == SND_SEQ_EVENT_NOTEON) ||
 		(ev->type == SND_SEQ_EVENT_NOTEOFF))
 	{
 		const char *type = (ev->type==SND_SEQ_EVENT_NOTEON) ? "on " : "off";
-		printf("[%d] Note %s: %d, 0x%2x vel(%2x)\n",
-				ev->time.tick, type,
+		printf("[%d] Note %s: %d, 0x%2x vel(%2x), channel: %d\n",
+				ev->time.tick,
+				type,
 				ev->data.note.note,
 				ev->data.note.note,
-				ev->data.note.velocity);
-		note = ev->data.note.note;
+				ev->data.note.velocity,
+				ev->data.note.channel);
+
+		nev.note = ev->data.note.note;
+		nev.channel = ev->data.note.channel;
+		nev.note_on = (ev->type == SND_SEQ_EVENT_NOTEON) ? true : false;
 	}
 	else if(ev->type == SND_SEQ_EVENT_CONTROLLER)
 	{
@@ -92,7 +97,7 @@ midiProcess(const snd_seq_event_t* ev)
 		printf("[%d] Unknown:  Unhandled Event Received\n", ev->time.tick);
 	}
 
-	return note;
+	return nev;
 }
 
 i32

src/midi.h

@@ -14,11 +14,18 @@ struct alsa_sequencer
 	snd_seq_addr_t dest;
 };
 
+struct alsa_note_event
+{
+	u8 note;
+	u8 channel;
+	bool note_on;
+};
+
 
 bool midiOpen(alsa_sequencer* seq);
 
 bool midiConnect(alsa_sequencer* seq, const char* midi_device);
 
-i32 midiProcess(const snd_seq_event_t* ev);
+alsa_note_event midiProcess(const snd_seq_event_t* ev);
 
 i32 midiClose(alsa_sequencer* seq);

src/spi.cpp

@@ -1,6 +1,7 @@
 
 #include <cassert>
 #include <cstdio>
+#include <cstring>
 #include <fcntl.h>
 #include <unistd.h>
 #include <linux/types.h>
@@ -9,6 +10,57 @@
 #include "spi.h"
 
 
+// GPIO
+
+bool
+gpioInit(gpio_info* gpio, const char* chip_name, u32 line_num)
+{
+	strncpy(gpio->chip_name, chip_name, sizeof(gpio->chip_name));
+	gpio->line_num = line_num;
+	gpio->chip = gpiod_chip_open_by_name(gpio->chip_name);
+
+	if (!gpio->chip) {
+		printf("Error opening chip, %s\n", gpio->chip_name);
+		return false;
+	}
+
+	gpio->line = gpiod_chip_get_line(gpio->chip, line_num);
+
+	if (!gpio->line) {
+		printf("Error opening line, chip: %s, line: %d\n", gpio->chip_name, line_num);
+		gpiod_chip_close(gpio->chip);
+		return false;
+	}
+
+	i32 ret = gpiod_line_request_output(gpio->line, "Consumer", 0);
+
+	if (ret < 0) {
+		printf("Error setting line output, chip: %s, line: %d\n", gpio->chip_name, line_num);
+		gpiod_line_release(gpio->line);
+		gpiod_chip_close(gpio->chip);
+		return false;
+	}
+
+	return true;
+}
+
+bool
+gpioSetValue(gpio_info* gpio, u32 value)
+{
+	assert(gpio);
+	i32 ret = gpiod_line_set_value(gpio->line, value);
+
+	if (ret < 0) {
+		printf("Error setting line value, chip: %s, line: %d\n", gpio->chip_name, gpio->line_num);
+		return false;
+	}
+
+	return true;
+}
+
+
+// SPI
+
 i32 open_device(u8 channel, u32 speed, u8 mode_flags);
 
 

src/spi.h

@@ -3,10 +3,28 @@
 
 #include <linux/spi/spi.h>
 #include <linux/spi/spidev.h>
+#include <gpiod.h>
 
 #include "types.h"
 
 
+// GPIO
+
+struct gpio_info
+{
+	char chip_name[16];
+	u32 line_num;
+	gpiod_chip* chip;
+	gpiod_line* line;
+};
+
+bool gpioInit(gpio_info* gpio, const char* chip_name, u32 line_num);
+
+bool gpioSetValue(gpio_info* gpio, u32 value);
+
+
+// SPI
+
 struct spi_connection
 {
 	i32 fd;
@@ -17,7 +35,6 @@ struct spi_connection
 	u8* buffer;
 };
 
-
 spi_connection spiInit(u32 speed, u32 max_dac_input, u8* buf, u32 buf_len, u8 flags, u8 channel);
 
 bool spiWrite(i32 fd, u32 speed, u8* buf, u32 buf_len);