sdr.c

/*  lysdr Software Defined Radio
	(C) 2010-2011 Gordon JC Pearce MM0YEQ and others
	
	sdr.c
	handle the actual audio processing, and creation and destruction of
	the SDR environment
	
	This file is part of lysdr.

	lysdr is free software: you can redistribute it and/or modify
	it under the terms of the GNU General Public License as published by
	the Free Software Foundation, either version 2 of the License, or
	any later version.

	lysdr is distributed in the hope that it will be useful, but
	WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	GNU General Public License for more details.

	You should have received a copy of the GNU General Public License
	along with lysdr.  If not, see <http://www.gnu.org/licenses/>.
*/
#include <stdlib.h>
#include <math.h>
#include <complex.h>
#include <fftw3.h>
#include <string.h>

#include "filter.h"
#include "sdr.h"

static gint blk_pos=0;
static int n;
	
sdr_data_t *sdr_new(gint fft_size) {
	// create an SDR, and initialise it
	sdr_data_t *sdr;
	
	sdr = malloc(sizeof(sdr_data_t));
	sdr->loVector = 1;  // start the local oscillator
	//sdr->loPhase = 1;   // this value is bogus but we're going to set the frequency anyway
	
	
	sdr->loPhase = cexp(I);
	sdr->agc_gain = 0;   // start off as quiet as possible
	sdr->mode = SDR_LSB;
	sdr->agc_speed = 0.005;
	sdr->fft_size = fft_size;
	
	return sdr; 
}

void sdr_destroy(sdr_data_t *sdr) {
	if (sdr) {
		free(sdr);
	}
}

int sdr_process(sdr_data_t *sdr) {
	// actually do the SDR bit
	int i, j, k;
	double y, accI, accQ;
	double complex c;
	fft_data_t *fft = sdr->fft;
	int size = sdr->size;
	int block_size = MIN(size, sdr->fft_size);   // ensure we don't try to copy a block larger than FFT_SIZE
	
	float agc_gain = sdr->agc_gain;
	float agc_peak = 0;

	// remove DC with a highpass filter
	for (i = 0; i < size; i++) {	   // DC removal; R.G. Lyons page 553
		c = sdr->iqSample[i] + sdr->dc_remove * 0.95;
		sdr->iqSample[i] = c - sdr->dc_remove;
		sdr->dc_remove = c;
	}

	// copy this period to FFT buffer, or as much as will fit
	// note that if the jack periodsize is greater than FFT_LEN, it will only copy FFT_LEN samples
	memmove(fft->samples, fft->samples+block_size, sizeof(double complex)*(sdr->fft_size-block_size)); // move the last lot up
	memmove(fft->samples+sdr->fft_size-block_size, sdr->iqSample, sizeof(double complex)*block_size);  // copy the current block



	// shift frequency
	for (i = 0; i < size; i++) {
		sdr->iqSample[i] *= sdr->loVector;
		sdr->loVector *= sdr->loPhase;
	}

	// demodulate by performing a Hilbert transform and then summing real and imaginary
	switch(sdr->mode) {
		case SDR_LSB:
			filter_hilbert(-1, sdr->iqSample, size);
			break;
		case SDR_USB:
			filter_hilbert(1, sdr->iqSample, size);
			break;
	} 
	for (i=0; i < size; i++) {
		 y = creal(sdr->iqSample[i])+cimag(sdr->iqSample[i]);
		sdr->output[i] = y;
	}

	//filter_iir_process(sdr->filter, sdr->output);
	
	// apply some AGC here
	for (i = 0; i < size; i++) {
		y = sdr->output[i];
		if (agc_peak < y) agc_peak = y;

	}
	

	if (agc_peak == 0) agc_peak = 0.00001;	// don't be zero, in case we have digital silence
	y = agc_peak * agc_gain;  // y is the peak level scaled by the current gain

	if (sdr->agc_speed < 0) {
		// AGC locked; don't change
	} else if (y <= 1) {	   // Current level is below the soundcard max, increase gain
		agc_gain += (1/ agc_peak - agc_gain) * sdr->agc_speed;
	} else {				   // decrease gain
		agc_gain += (1 / agc_peak - agc_gain);
	}
	y = agc_gain * 0.5; // change volume
	for (i = 0; i < sdr->size; i++){
		sdr->output[i] *= y;
	}
	
	sdr->agc_gain = agc_gain;

	return 0;
}

void fft_setup(sdr_data_t *sdr) {
	sdr->fft = (fft_data_t *)malloc(sizeof(fft_data_t));
	fft_data_t *fft = sdr->fft;

	fft->filter = (fftw_complex*) fftw_malloc(sizeof(fftw_complex) * sdr->fft_size);

	fft->windowed = (fftw_complex*) fftw_malloc(sizeof(fftw_complex) * sdr->fft_size);	
	fft->samples = (fftw_complex*) fftw_malloc(sizeof(fftw_complex) * sdr->fft_size);
	fft->out = (fftw_complex*) fftw_malloc(sizeof(fftw_complex) * sdr->fft_size);
	fft->plan = fftw_plan_dft_1d(sdr->fft_size, fft->windowed, fft->out, FFTW_FORWARD, FFTW_ESTIMATE);
	fft->htplan = fftw_plan_dft_1d(sdr->fft_size, sdr->iqSample, fft->filter, FFTW_FORWARD, FFTW_ESTIMATE);
	fft->htbplan = fftw_plan_dft_1d(sdr->fft_size, fft->filter, sdr->iqSample, FFTW_BACKWARD, FFTW_ESTIMATE);
	fft->status = EMPTY;
	fft->index = 0;
}

void fft_teardown(sdr_data_t *sdr) {
	fft_data_t *fft = sdr->fft;
	fftw_destroy_plan(fft->plan);
	fftw_destroy_plan(fft->htplan);
	fftw_destroy_plan(fft->htbplan);
	fftw_free(fft->filter);
	fftw_free(fft->windowed);
	fftw_free(fft->samples);
	fftw_free(fft->out);
	free(sdr->fft);
}

/* vim: set noexpandtab ai ts=4 sw=4 tw=4: */