beeper.h

#pragma once
#ifndef BEEPER_H
#define BEEPER_H

/*
 beeper.h    -- simple square-wave beeper
 
 TODO: docs
 
 ## zlib/libpng license
 
 Copyright (c) 2018 Andre Weissflog
 This software is provided 'as-is', without any express or implied warranty.
 In no event will the authors be held liable for any damages arising from the
 use of this software.
 Permission is granted to anyone to use this software for any purpose,
 including commercial applications, and to alter it and redistribute it
 freely, subject to the following restrictions:
 1. The origin of this software must not be misrepresented; you must not
 claim that you wrote the original software. If you use this software in a
 product, an acknowledgment in the product documentation would be
 appreciated but is not required.
 2. Altered source versions must be plainly marked as such, and must not
 be misrepresented as being the original software.
 3. This notice may not be removed or altered from any source
 distribution.
 */
#include <stdint.h>
#include <stdbool.h>

#ifdef __cplusplus
extern "C" {
#endif
	
	// error-accumulation precision boost
#define BEEPER_FIXEDPOINT_SCALE (1000)
	// DC adjust buffer size
#define BEEPER_DCADJ_BUFLEN (256)
	
	// initialization parameters
	typedef struct {
		float tick_hz;
		int sound_hz;
		float base_volume;
	} beeper_desc_t;
	
	// beeper state
	typedef struct {
		int state;
		int period;
		int counter;
		float base_volume;
		float volume;
		float sample;
		float dcadj_sum;
		uint32_t dcadj_pos;
		float dcadj_buf[BEEPER_DCADJ_BUFLEN];
	} beeper_t;
	
	// initialize beeper instance
	void beeper_init(beeper_t* beeper, const beeper_desc_t* desc);
	// reset the beeper instance
	void beeper_reset(beeper_t* beeper);
	// set current on/off state
	static inline void beeper_set(beeper_t* beeper, bool state) {
		beeper->state = state ? 1 : 0;
	}
	// toggle current state (on->off or off->on)
	static inline void beeper_toggle(beeper_t* beeper) {
		beeper->state = 1 - beeper->state;
	}
	// set current volume 0.0 to 1.0
	static inline void beeper_set_volume(beeper_t* beeper, float vol) {
		beeper->volume = vol;
	}
	// tick the beeper, return true if a new sample is ready
	bool beeper_tick(beeper_t* beeper);
	
#ifdef __cplusplus
} /* extern "C" */
#endif
/*-- IMPLEMENTATION ----------------------------------------------------------*/
#ifdef CHIPS_IMPL
#include <string.h>
#ifndef CHIPS_ASSERT
#include <assert.h>
#define CHIPS_ASSERT(c) assert(c)
#endif

void beeper_init(beeper_t* b, const beeper_desc_t* desc) {
	CHIPS_ASSERT(b && desc);
	CHIPS_ASSERT((desc->tick_hz > 0) && (desc->sound_hz > 0));

	b->period = ((int)(desc->tick_hz * BEEPER_FIXEDPOINT_SCALE)) / desc->sound_hz;
	b->counter = b->period;
	b->base_volume = desc->base_volume;
	b->volume = 1.0f;
}

void beeper_reset(beeper_t* b) {
	CHIPS_ASSERT(b);
	b->state = 0;
	b->counter = b->period;
	b->sample = 0;
}

/* DC adjustment filter from StSound, this moves an "offcenter"
 signal back to the zero-line (e.g. the volume-level output
 from the chip simulation which is >0.0 gets converted to
 a +/- sample value)
 */
static void _beeper_dcadjust(beeper_t* bp, float s) {
	bp->dcadj_sum -= bp->dcadj_buf[bp->dcadj_pos];
	bp->dcadj_sum += s;
	bp->dcadj_buf[bp->dcadj_pos] = s;
	bp->dcadj_pos = (bp->dcadj_pos + 1) & (BEEPER_DCADJ_BUFLEN-1);
}

bool beeper_tick(beeper_t* bp) {
	_beeper_dcadjust(bp, (float)bp->state * bp->volume * bp->base_volume);
	/* generate a new sample? */
	bp->counter -= BEEPER_FIXEDPOINT_SCALE;
	if (bp->counter <= 0) {
		bp->counter += bp->period;
		bp->sample = bp->dcadj_sum / BEEPER_DCADJ_BUFLEN;
		return true;
	}
	return false;
}


#endif /* CHIPS_IMPL */

#endif /* BEEPER_H */