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◆ main x16-emulator / src / vera_pcm.c
3.0 KiB · C · last changed chore(): initial commit 15 days ago source blame history raw
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// Commander X16 Emulator
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// Copyright (c) 2020 Frank van den Hoef
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// All rights reserved. License: 2-clause BSD
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#include "vera_pcm.h"
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#include <stdio.h>
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static uint8_t  fifo[4096];
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static unsigned fifo_wridx;
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static unsigned fifo_rdidx;
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static unsigned fifo_cnt;
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static uint8_t ctrl;
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static uint8_t rate;
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static uint8_t loop;
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static uint8_t volume_lut[16] = {0, 1, 2, 3, 4, 5, 6, 8, 11, 14, 18, 23, 30, 38, 49, 64};
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static int16_t cur_l, cur_r;
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static uint8_t phase;
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static void
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fifo_reset(void)
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{
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	fifo_wridx = 0;
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	fifo_rdidx = 0;
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	fifo_cnt   = 0;
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}
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static void
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fifo_restart(void)
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{
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	fifo_rdidx = 0;
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	fifo_cnt = fifo_wridx;
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}
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void
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pcm_reset(void)
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{
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	fifo_reset();
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	ctrl  = 0;
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	rate  = 0;
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	cur_l = 0;
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	cur_r = 0;
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	phase = 0;
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}
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void
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pcm_write_ctrl(uint8_t val)
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{
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	if ((val & 0xc0) == 0xc0) {
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		loop = true;
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	} else {
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		loop = false;
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		if (val & 0x80) {
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			fifo_reset();
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		}
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	}
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	if (val & 0x40) {
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		fifo_restart();
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	}
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	ctrl = val & 0x3F;
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}
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uint8_t
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pcm_read_ctrl(void)
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{
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	uint8_t result = ctrl;
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	if (fifo_cnt == sizeof(fifo) - 1) {
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		result |= 0x80;
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	}
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	if (fifo_cnt == 0) {
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		result |= 0x40;
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	}
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	return result;
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}
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void
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pcm_write_rate(uint8_t val)
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{
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	rate = (val > 128) ? (256 - val) : val;
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}
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uint8_t
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pcm_read_rate(void)
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{
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	return rate;
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}
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void
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pcm_write_fifo(uint8_t val)
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{
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	if (fifo_cnt < sizeof(fifo) - 1) {
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		fifo[fifo_wridx++] = val;
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		if (fifo_wridx == sizeof(fifo)) {
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			fifo_wridx = 0;
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		}
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		fifo_cnt++;
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	}
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}
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static uint8_t
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read_fifo()
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{
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	static uint8_t result = 0;
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	if (fifo_cnt == 0) {
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		return 0;
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	}
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	result = fifo[fifo_rdidx++];
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	if (fifo_rdidx == sizeof(fifo)) {
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		fifo_rdidx = 0;
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	}
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	fifo_cnt--;
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	return result;
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}
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bool
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pcm_is_fifo_almost_empty(void)
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{
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	return fifo_cnt < 1024;
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}
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void
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pcm_render(int16_t *buf, unsigned num_samples)
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{
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	while (num_samples--) {
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		uint8_t old_phase = phase;
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		phase += rate;
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		if ((old_phase & 0x80) != (phase & 0x80)) {
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			if (fifo_cnt == 0) {
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				cur_l = 0;
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				cur_r = 0;
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			} else {
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				switch ((ctrl >> 4) & 3) {
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					case 0: { // mono 8-bit
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						cur_l = (int16_t)read_fifo() << 8;
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						cur_r = cur_l;
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						break;
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					}
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					case 1: { // stereo 8-bit
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						if (fifo_cnt < 2) {
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							fifo_cnt = 0;
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							fifo_rdidx = fifo_wridx;
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						} else {
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							cur_l = read_fifo() << 8;
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							cur_r = read_fifo() << 8;
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						}
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						break;
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					}
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					case 2: { // mono 16-bit
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						if (fifo_cnt < 2) {
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							fifo_cnt = 0;
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							fifo_rdidx = fifo_wridx;
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						} else {
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							cur_l = read_fifo();
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							cur_l |= read_fifo() << 8;
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							cur_r = cur_l;
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						}
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						break;
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					}
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					case 3: { // stereo 16-bit
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						if (fifo_cnt < 4) {
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							fifo_cnt = 0;
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							fifo_rdidx = fifo_wridx;
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						} else {
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							cur_l = read_fifo();
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							cur_l |= read_fifo() << 8;
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							cur_r = read_fifo();
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							cur_r |= read_fifo() << 8;
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						}
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						break;
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					}
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				}
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				if (loop && fifo_cnt == 0) {
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					fifo_restart();
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				}
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			}
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		}
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		*(buf++) = (int16_t)((int32_t)cur_l * volume_lut[ctrl & 0xF] / 64);
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		*(buf++) = (int16_t)((int32_t)cur_r * volume_lut[ctrl & 0xF] / 64);
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	}
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}