pentabug/firmware/lib/synth.c

#include <inttypes.h>
#include "synth.h"
#include "freq_table.h"
#include <avr/pgmspace.h>
#include <avr/interrupt.h>

// sample rate is 8M / (3 * 64)

enum {
	channel_count = 3,
	//tick_length = 400,
//	tick_length = 256,
	row_length = 4,
	pattern_length = 16
};

static const synth_instrument_t instruments[] = { { 1 << 15, 100, 12, 0 }, { 0,
		100, 12, 0 }, { 0, 200, 10, 0 }, { 1 << 13, 0, 0, 2 }, { 1 << 13, 0, 5,
		2 }, };

static const uint8_t wave_table[][2] = { { 0, WAVE_PULSE }, { 3, WAVE_PULSE }, {
		7, WAVE_PULSE }, { 12, WAVE_PULSE }, { 256 - 4, 0xff },

{ 0, WAVE_PULSE }, { 2, WAVE_PULSE }, { 7, WAVE_PULSE }, { 10, WAVE_PULSE }, {
		256 - 4, 0xff },

{ 0, WAVE_NOISE }, { 0, WAVE_PULSE }, { 0xff, 0xff },

{ 0, WAVE_PULSE }, { 0xff, 0xff },

};

static const uint8_t patterns[][pattern_length][2] PROGMEM = { { }, { { 33 - 12,
		0 }, { 0, 0 }, { 0xff, 1 }, { 0, 0 }, { 33, 1 }, { 0xff, 1 }, { 33, 1 },
		{ 0xff, 1 }, { 33, 1 }, { 0xff, 1 }, { 33 - 12, 1 }, { 0xff, 1 }, { 33
				- 12, 1 }, { 0xff, 1 }, { 33, 1 }, { 0xff, 1 }, }, { { 28 - 12,
		0 }, { 0, 0 }, { 0xff, 1 }, { 0, 0 }, { 28, 1 }, { 0xff, 1 }, { 28, 1 },
		{ 0xff, 1 }, { 28, 1 }, { 0xff, 1 }, { 28 - 12, 1 }, { 0xff, 1 }, { 28
				- 12, 1 }, { 0xff, 1 }, { 28, 1 }, { 0xff, 1 }, }, { { 0, 0 }, {
		0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, {
		57, 3 }, }, { { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 },
		{ 0, 0 }, { 0, 0 }, { 0, 0 }, { 57, 4 }, },

{ { 60, 2 }, }, { { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 57, 2 }, { 0, 0 }, {
		0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 55, 2 }, {
		0, 0 }, { 57, 2 }, { 0, 0 }, }, { { 55, 2 }, }, { { 0, 0 }, { 0, 0 }, {
		0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0,
		0 }, { 0, 0 }, { 0, 0 }, { 57, 2 }, }, { { 55 - 3, 2 }, },

};

static const uint8_t pattern_table[][channel_count] = { { 1, 0, 5 },
		{ 1, 3, 0 }, { 1, 0, 7 }, { 1, 3, 6 }, { 2, 0, 7 }, { 2, 4, 8 }, { 2, 0,
				9 }, { 2, 4, 0 }, };
enum {
	pattern_table_length = sizeof(pattern_table) / sizeof(pattern_table[0])
};

static synth_channel_t channels[channel_count];
static int8_t sample;
static int8_t tick;
static int8_t row;
static int8_t seq;

/* PROTOTYPES */
uint8_t synth_mix(void);

static uint8_t timeslots[SYNTH_BUFSIZE];
static uint8_t timeslots_write; // current write head 
static uint8_t timeslots_read; // current read head 

/*register for atomic ++ and -- */
register uint8_t timeslots_fill asm("r2");

static void enqueue_timeslot(uint8_t synthval);
static uint8_t dequeue_timeslot(void);

void synth_init(void) {
	sample = 0;
	tick = 0;
	row = 0;
	seq = 0;
	timeslots_fill = 0;
}

inline uint8_t synth_mix(void) {
	if (sample == 0) { // new tick
		for (int i = 1; i < channel_count; i++) {
			synth_channel_t* chan = &channels[i];

			const synth_instrument_t* inst = &instruments[chan->inst_nr];

			if (chan->level > inst->decay)
				chan->level -= inst->decay;
			else
				chan->level = 0;

			chan->pulse_width += inst->pulse_sweep;

			chan->pos++;
			if (wave_table[chan->pos][1] == 0xff)
				chan->pos += wave_table[chan->pos][0];

			// enter new rol
			// w
			if (tick == 0) {
				uint8_t pattern_nr = pattern_table[seq][i];
				uint8_t note = pgm_read_byte(&patterns[pattern_nr][row][0]);

				if (note) { // new note, maybe?
					if (note == 0xff) {
						chan->level = 0;
					} else {
						chan->level = 80; // TODO: less?
						chan->note = note;
						chan->inst_nr =
								pgm_read_byte(&patterns[pattern_nr][row][1]);
						inst = &instruments[chan->inst_nr];
						chan->pos = inst->wave_table_pos;
						if (inst->pulse_width)
							chan->pulse_width = inst->pulse_width;
					}
				}
			}
		}
	}
	if (++sample == 0) {
		if (++tick == row_length) {
			tick = 0;
			if (++row == pattern_length) {
				row = 0;
				if (++seq == pattern_table_length) {
					seq = 0;
				}
			}
		}
	}

	uint8_t output = 0;
	for (int i = 0; i < channel_count; i++) {
		synth_channel_t* chan = &channels[i];
		//	const synth_instrument_t* inst = &instruments[chan->inst_nr];

		chan->phase +=
				pgm_read_word(&freq_table[(uint8_t)(chan->note + wave_table[chan->pos][0])]);

		uint8_t amp;
		switch (wave_table[chan->pos][1]) {
		case WAVE_PULSE:
			amp = -(chan->phase < chan->pulse_width);
			break;

		case WAVE_SAW:
			amp = (chan->phase >> 8);
			break;

		case WAVE_NOISE: // shitty noise
			chan->phase = (chan->phase >> 1) ^ (-(chan->phase & 1) & 0xb400);
			amp = (chan->phase >> 8);
			break;

		default:
			amp = 0;
			break;
		}

		output += (((amp & 0xff) * chan->level) >> 8);
	}

	return output;
}

/* fill all the timeslots */
inline void synth_poll(void) {
	/* refill timeslots queue */
//	while (timeslots_fill < (SYNTH_BUFSIZE-1))
	if (timeslots_fill < (SYNTH_BUFSIZE - 1))
		enqueue_timeslot(synth_mix());
}

/* timeslot queue handling */
static inline void enqueue_timeslot(uint8_t synthval) {
	timeslots[timeslots_write & SYNTH_BUFMASK] = synthval;
	timeslots_fill++;
	timeslots_write++;
}

static inline uint8_t dequeue_timeslot() {
	uint8_t t = timeslots[timeslots_read & SYNTH_BUFMASK];
	if (timeslots_fill) {
		/* buffer not underrun... move forward in readbuffer */

		timeslots_fill--;
		timeslots_read++;
	}

	return t;
}

ISR(TIMER0_COMPA_vect) {
	/* calculate next analog sample value in synth mixer:*/
	OCR1B = dequeue_timeslot();
}