SSB_HighSpeed_Modem/modem/fft.c
Kurt Moraw 3deb0a09fd update
2020-10-27 16:41:16 +01:00

141 lines
3.8 KiB
C

/*
* High Speed modem to transfer data in a 2,7kHz SSB channel
* =========================================================
* Author: DJ0ABR
*
* (c) DJ0ABR
* www.dj0abr.de
*
* This program 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
* (at your option) any later version.
*
* This program 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 this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*
*/
#include "qo100modem.h"
#include <fftw3.h>
#include <math.h>
#define AUDIOSAMPLERATE 8000
double *din = NULL; // input data for fft
fftw_complex *cpout = NULL; // ouput data from fft
fftw_plan plan = NULL;
#define fft_rate (AUDIOSAMPLERATE / 10) // resolution: 10 Hz
int fftidx = 0;
int fftcnt = fft_rate/2+1; // number of output values
uint16_t fftout[AUDIOSAMPLERATE / 10/2+1];
uint16_t *make_waterfall(uint8_t *pdata, int len, int *retlen)
{
int fftrdy = 0;
// get the real sample in float (imag is not required for the FFT)
int re=0;
// GR sends 8 Bytes containing 4x 0x000003e8 (marker) and 4x input-samples (real integer)
#define dlen 8
static uint8_t rbuf[dlen];
for(int i=0; i<len; i++)
{
// insert new byte in rbuf
for(int sh = (dlen-1); sh > 0; sh--)
rbuf[sh] = rbuf[sh - 1];
rbuf[0] = pdata[i];
// check for BIG/LITTLE endian
if(rbuf[0] == 0 && rbuf[1] == 0 && rbuf[2] == 3 && rbuf[3] == 0xe8)
{
re = rbuf[4];
re <<= 24;
re += rbuf[5];
re <<= 16;
re += rbuf[6];
re <<= 8;
re += rbuf[7];
}
else if(rbuf[0] == 0xe8 && rbuf[1] == 3 && rbuf[2] == 0 && rbuf[3] == 0)
{
re = rbuf[7];
re <<= 24;
re += rbuf[6];
re <<= 16;
re += rbuf[5];
re <<= 8;
re += rbuf[4];
}
else
continue;
// the value was scaled in GR by 2^24 = 16777216
// in order to send it in an INT
// undo this scaling
float fre = (float)re / 16777216;
// fre are the float samples
// fill into the fft input buffer
din[fftidx++] = fre;
if(fftidx == fft_rate)
{
fftidx = 0;
// the fft buffer is full, execute the FFT
fftw_execute(plan);
for (int j = 0; j < fftcnt; j++)
{
// calculate absolute value (magnitute without phase)
float fre = cpout[j][0];
float fim = cpout[j][1];
float mag = sqrt((fre * fre) + (fim * fim));
fftout[j] = (uint16_t)mag;
fftrdy = 1;
}
}
}
if(fftrdy == 1)
{
*retlen = fftcnt;
return fftout;
}
return NULL;
}
void init_fft()
{
char fn[300];
sprintf(fn, "capture_fft_%d", fft_rate); // wisdom file for each capture rate
fftw_import_wisdom_from_filename(fn);
din = (double *)fftw_malloc(sizeof(double) * fft_rate);
cpout = (fftw_complex *)fftw_malloc(sizeof(fftw_complex) * fft_rate);
plan = fftw_plan_dft_r2c_1d(fft_rate, din, cpout, FFTW_MEASURE);
fftw_export_wisdom_to_filename(fn);
}
void exit_fft()
{
if(plan) fftw_destroy_plan(plan);
if(din) fftw_free(din);
if(cpout) fftw_free(cpout);
}