midi_to_cv/src/main.cpp

//	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
//		the correct DAC value. Would then need to set Vref to:
//		DAC: 5V = 4080 / 4095 * Vref, Vref ~= 5.0184


#include <cstdio>
#include <cstdlib>

#include <unistd.h>
#include <linux/spi/spi.h>

#include "spi.h"
#include "midi.h"


#define SPI_SPEED 1000000
#define SPI_BUFFER_LENGTH 2
#define SPI_CHANNEL 0
#define SPI_FLAGS SPI_MODE_3|SPI_CS_HIGH

#define MIDI_NOTE_OFFSET 24
#define MIDI_NOTE_LENGTH 61

#define MAX_DAC_INPUT 4095 // 2^12 - 1


void
showUsage(const char* prog_name)
{
	printf("Usage: %s [options]\n", prog_name);
	printf("  options:\n");
	printf("    -t: cycle test voltages on DAC\n");
	printf("    -k sequencer-port: attempt to connect to port \n");
	printf("    -f midi-file: play the first track, first channel of a MIDI file\n");
	printf("    -h: show this help \n");
	printf("  example:\n");
	printf("    %s -k 20:0\n", prog_name);
	printf("    attempt to connect to MIDI input device on channel:port 20:0\n");
}

u32
convertNoteToDACInput(u8 midi_note)
{
	// NOTE: assuming
	// 	DAC: 5V = 4080 / 4095 * Vref, Vref ~= 5.0184
	// 	1 half step/note = 1/12V = dac 68
	// 	1 octave = 1V = dac 816
	u32 dac = midi_note * 68;
	(dac > MAX_DAC_INPUT) ? dac = MAX_DAC_INPUT : dac;

	return dac;
}

void
loopMIDI(alsa_sequencer* seq, spi_connection* spi)
{
	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);

			// TODO: could check return value here for SPI error
			spiSendVoltage(spi, dac_in);
		}
	}
}

i32
main(i32 argc, char* argv[])
{
	if (argc == 1) {
		showUsage(argv[0]);
		exit(0);
	}

	i32 opt = 0;
	alsa_sequencer seq = {0};
	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);

	if (spi.fd < 0) {
		printf("error opening SPI device\n");
		return 1;
	}

	if (!midiOpen(&seq))
		return 1;

	while ((opt = getopt(argc, argv, "tk:f:h")) != -1) {
		switch (opt) {
			case 'f':
				printf("TODO: parse and play sequence from midi file\n");
				break;
			case 'k':
				if (!midiConnect(&seq, optarg)) {
					printf("Error connecting to MIDI device, %s\n", optarg);
					exit(1);
				}

				loopMIDI(&seq, &spi);
				break;
			case 't':
				printf("TODO: cycle test voltages to SPI DAC\n");
				break;
			case 'h':
			default:
				showUsage(argv[0]);
				exit(1);
		}
	}

	midiClose(&seq);
	return spiClose(spi.fd);
}