rds95/src/modulator.c

#include "modulator.h"

static float waveform[2][FILTER_SIZE];

void init_rds_modulator(RDSModulator* rdsMod, RDSEncoder* enc) {
	memset(rdsMod, 0, sizeof(*rdsMod));
	rdsMod->level = 1.0f;
	rdsMod->rdsgen = 1;

	rdsMod->enc = enc;

	for (uint8_t i = 0; i < 2; i++) {
		for (uint16_t j = 0; j < FILTER_SIZE; j++) {
			waveform[i][j] = i ?
				+waveform_biphase[j] : -waveform_biphase[j];
		}
	}
}

float get_rds_sample(RDSModulator* rdsMod) {
	uint16_t idx;
	float *cur_waveform;
	float sample;
	if (rdsMod->sample_count == SAMPLES_PER_BIT) {
		if (rdsMod->bit_pos == BITS_PER_GROUP) {
			get_rds_bits(rdsMod->enc, rdsMod->bit_buffer);
			rds.bit_pos = 0;
		}

		rdsMod->cur_bit = rdsMod->bit_buffer[rdsMod->bit_pos++];
		rdsMod->prev_output = rdsMod->cur_output;
		rdsMod->cur_output = rdsMod->prev_output ^ rdsMod->cur_bit;

		idx = rdsMod->in_sample_index;
		cur_waveform = waveform[rdsMod->cur_output];

		for (uint16_t i = 0; i < FILTER_SIZE; i++) {
			rdsMod->sample_buffer[idx++] += *cur_waveform++;
			if (idx == SAMPLE_BUFFER_SIZE) idx = 0;
		}

		rdsMod->in_sample_index += SAMPLES_PER_BIT;
		if (rdsMod->in_sample_index == SAMPLE_BUFFER_SIZE) rdsMod->in_sample_index = 0;

		rdsMod->sample_count = 0;
	}
	rdsMod->sample_count++;

	sample = rdsMod->sample_buffer[rdsMod->out_sample_index];

	rdsMod->sample_buffer[rdsMod->out_sample_index++] = 0;
	if (rdsMod->out_sample_index == SAMPLE_BUFFER_SIZE)
		rdsMod->out_sample_index = 0;
	return sample*rdsMod->level*rdsMod->rdsgen;
}