111 lines
1.7 KiB
C
111 lines
1.7 KiB
C
#include <inttypes.h>
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// sample rate is 8M / (3 * 64)
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enum { WAVE_PULSE, WAVE_SAW, WAVE_NOISE };
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typedef struct {
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uint8_t wave;
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uint16_t phase;
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uint16_t speed;
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uint32_t pulse_width;
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uint8_t pulse_sweep;
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uint8_t level; // envelop level
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} synth_channel_t;
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enum {
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synth_channel_count = 2,
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tick_length = 500,
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row_length = 6,
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pattern_length = 16
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};
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typedef struct {
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synth_channel_t channels[synth_channel_count];
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int16_t sample;
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int8_t tick;
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int8_t row;
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int8_t seq;
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} synth_t;
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static synth_t synth;
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void synth_init(void)
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{
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// some test values
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synth.channels[0].wave = WAVE_PULSE;
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synth.channels[0].speed = 1153;
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synth.channels[0].pulse_sweep = 0;
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synth.channels[0].pulse_width = 1 << 31;
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synth.channels[1].wave = WAVE_SAW;
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synth.channels[1].speed = 1728;
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}
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uint16_t synth_mix(void)
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{
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if(synth.sample == 0) {
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// new tick
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if(synth.tick == 0) {
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// new row
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if(synth.row == 0) {
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// new pattern
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}
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}
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}
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if(++synth.sample == tick_length) {
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synth.sample = 0;
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if(++synth.tick == row_length) {
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synth.tick = 0;
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if(++synth.row == pattern_length) {
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synth.row = 0;
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}
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}
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}
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uint16_t output = 0;
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for(int i = 0; i < synth_channel_count; i++) {
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synth_channel_t *chan = &synth.channels[i];
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chan->phase += chan->speed;
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chan->pulse_width += chan->pulse_sweep << 8;
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uint8_t amp;
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switch(chan->wave) {
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case WAVE_PULSE:
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amp = -(chan->phase < (chan->pulse_width >> 16));
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break;
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case WAVE_SAW:
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amp = (chan->phase >> 8);
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break;
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case WAVE_NOISE: // shitty noise
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chan->phase = (chan->phase >> 1) ^ (-(chan->phase & 1) & 0xb400);
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amp = (chan->phase >> 8);
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break;
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default:
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amp = 0;
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break;
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}
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output += (amp & 0xff) / 2;
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}
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return output;
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}
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