Changed FSK demodulator to use s16/7200 at will.
This commit is contained in:
Andreas Beck
parent
93427029cb
commit
21e4f59a95
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@ -1,6 +1,14 @@
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Changelog:
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----------
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99-07-02 [becka]:
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* Changes to fsk_demod:
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- First parameter at creation now gives samplerate. Allows for
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7200 samples/second.
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- Changed demodulator to read signed 16 encoded data. Hope that
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works.
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- Heavily commented it.
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99-07-01 [morten]:
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* Added new framework for State-machines, see misc/statemachines.c
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and G3/fsm.c
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@ -2,10 +2,18 @@
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******************************************************************************
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Fax program for ISDN.
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FSK demodulator. Takes alaw data and demodulates it to a stream of
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0/1,conf pairs.
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FSK demodulator. Takes signed 16 bit data and demodulates it to a
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stream of bytes containing 0/1,conf pairs.
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conf is a "confidence value" ranging from 0-100% giving you an idea
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about how sure the demodulator is about the result. Extended periods
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of low confidence usually indicate carrier loss. Short periods are
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normal when the transmitted symbol changes. This behaviour can be used
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to re-lock PLLs.
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We do a s16->alaw conversion here to allow for table lookup.
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This is suboptimal as we then do alaw->s16->alaw.
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Copyright (C) 1998 Andreas Beck [becka@ggi-project.org]
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Copyright (C) 1999 Andreas Beck [becka@ggi-project.org]
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Permission is hereby granted, free of charge, to any person obtaining a
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copy of this software and associated documentation files (the "Software"),
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@ -34,33 +42,50 @@
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#include <stdarg.h>
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#include <sys/times.h>
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#include <ifax/ifax.h>
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#include <ifax/alaw.h>
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/* Turn on to generate a big bunch of debugging code.
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*/
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#undef BIGDEBUG
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/* Data structures for the fourier analysis.
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*/
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typedef struct four_help {
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int depth,depthsquare,currpos;
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int currreal,currimag;
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char *histreal,*histimag;
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int stpos,ctpos,stdepth;
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char *fasttable;
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int depth, /* width of the fourier window */
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depthsquare, /* square of it. Used for normalizing */
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currpos; /* sliding pointer into the history */
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int currreal,currimag; /* The current real and imaginary parts of
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the fourier transform. */
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char *histreal,*histimag;/* History over the window to be able to
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remove the coefficients when they
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slide out of the window */
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int stpos,ctpos,stdepth;/* Offsets for the current sine-position,
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the cosine position (shifted by pi/4)
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and the depth of the table. */
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char *fasttable; /* Lookup table for the multiplication
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in the DFT. Directly gives
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sin(omega*t)*i(t) */
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} four_help;
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/* private data of a fsk_demod module.
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*/
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typedef struct {
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four_help freq1,freq2;
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int f1,f2;
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int baud;
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four_help freq1,freq2; /* fourier data for both channels */
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int f1,f2; /* frequencies for 1 and 0 */
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int baud; /* baudrate - gives fourier window */
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int sps; /* samples per second */
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} fskdemod_private;
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/* Calculate the greatest common divisor. This is used to see when a waveform
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* repeats. This optimizes the length of the waveform table.
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* Euclidian algorithm.
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*/
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int gcd(int d1,int d2)
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{
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/* FIXME ! Is this correct ? Pretty long ago that I did that last time ... */
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while(d1!=d2)
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{
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if (d1>d2) d1-=d2;
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@ -73,36 +98,58 @@ int gcd(int d1,int d2)
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/* The following do the DFT "on the fly" with a sliding window.
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*/
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static void init_four_help(four_help *hlp,int depth,int freq)
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/* Set up all the tables.
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*/
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static void init_four_help(fskdemod_private *priv,four_help *hlp,int depth,int freq)
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{
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int x,y;
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char *ftptr;
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double sinval;
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hlp->depth=depth;
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hlp->depthsquare=depth*depth;
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hlp->currpos=0;
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hlp->currreal=hlp->currimag=0;
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hlp->depth=depth; /* window size */
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hlp->depthsquare=depth*depth; /* normalizing helper variable */
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hlp->currpos=0; /* window initial position. */
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hlp->currreal=hlp->currimag=0; /* there is no energy in a zero window */
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/* Allocate the history windows and erase them. */
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hlp->histreal=malloc(sizeof(hlp->histreal[0])*depth);
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hlp->histimag=malloc(sizeof(hlp->histimag[0])*depth);
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while(depth--)
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hlp->histreal[depth]=
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hlp->histimag[depth]=0;
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x=gcd(freq,SAMPLES_PER_SECOND);x=SAMPLES_PER_SECOND/x;
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/* Calculate size of the sine lookup tables. At worst this is
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sps, if they have no common divisor (we have no fractional
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rates, so after 1 second we must have a match again).
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As this is pretty large like 8000sps*256values=2MB, we try to
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optimize by finding the GCD which gives the fraction of seconds
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after which the frequency pattern repeats at the samplerate.
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*/
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x=gcd(freq,priv->sps);x=priv->sps/x;
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/* We derive the cosine part by shifting by PI/4. If that doesn't
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* compute, we have a slight error. Warn about that. All V.21
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* signals at 8000 or 7200 sps will not trigger that case.
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*/
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if (x%4) {
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fprintf(stderr,"fsk_demod: ERROR: sinetable size not divideable by 4.\n"
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"Cosine shift is slighty incorrect.\n");
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}
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/* The table is 256 entries per sample */
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hlp->stdepth=256*x;
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hlp->stpos=0;
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hlp->ctpos=256*(x/4); /* The bracket _IS_ important. Do not optimize. */
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/* Allocate and fill the table. The table contains sin(omega*t)*i(t)
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* and is accessed by t*256+i(t), where i(t) is assumed to be alaw-
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* encoded for better dynamics. Any encoding would do. Just make sure
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* you choose the same encoding in add_samp.
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*/
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hlp->fasttable=malloc(sizeof(hlp->fasttable[0])*hlp->stdepth);
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ftptr=hlp->fasttable;
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for(x=0;x<hlp->stdepth/256;x++)
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{
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sinval=sin(x*2.0*M_PI*(double)freq/(double)SAMPLES_PER_SECOND);
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sinval=sin(x*2.0*M_PI*(double)freq/(double)priv->sps);
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for(y=0;y<256;y++)
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*ftptr++=((int)(sinval*alaw2int(y))) >>
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((sizeof(int)-sizeof(char))*8);
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@ -118,21 +165,39 @@ static void destroy_four_help(four_help *hlp)
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free(hlp->fasttable);hlp->fasttable=NULL;
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}
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inline void add_samp(four_help *hlp,char sample)
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/* Slide the DFT window by one sample.
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*/
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inline void add_samp(four_help *hlp,ifax_sint16 sample)
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{
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unsigned char mysample;
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/* convert sample to alaw for table lookup.
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*/
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mysample=sint2wala[((unsigned)sample>>4)&0xFFF];
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/* remove old sample that slides out of the window.
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* We could optimize a little further here by directly storing
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* the power instead of the individual values, but I prefer to
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* keep the information. We could easily modify this system to
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* demodulate a PSK stream this way.
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*/
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hlp->currreal-=hlp->histreal[hlp->currpos];
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hlp->currimag-=hlp->histimag[hlp->currpos];
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/* Add and store new samples using the lookup-tables. */
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hlp->currreal+=
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(hlp->histreal[hlp->currpos]=hlp->fasttable[hlp->stpos+(unsigned char)sample]);
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(hlp->histreal[hlp->currpos]=hlp->fasttable[hlp->stpos+(unsigned char)mysample]);
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hlp->currimag+=
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(hlp->histimag[hlp->currpos]=hlp->fasttable[hlp->ctpos+(unsigned char)sample]);
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(hlp->histimag[hlp->currpos]=hlp->fasttable[hlp->ctpos+(unsigned char)mysample]);
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/* Slide on the table pointers. */
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hlp->currpos++ ;if (hlp->currpos>=hlp->depth ) hlp->currpos=0;
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hlp->stpos+=256;if (hlp->stpos >=hlp->stdepth) hlp->stpos=0;
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hlp->ctpos+=256;if (hlp->ctpos >=hlp->stdepth) hlp->ctpos=0;
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}
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/* Destroy the private data.
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*/
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void fskdemod_destroy(ifax_modp self)
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{
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fskdemod_private *priv=(fskdemod_private *)self->private;
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@ -144,15 +209,20 @@ void fskdemod_destroy(ifax_modp self)
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return;
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}
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/* Module has no commands.
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*/
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int fskdemod_command(ifax_modp self,int cmd,va_list cmds)
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{
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return 0; /* Not yet used. */
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}
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/* Handler - go through the data, slide it into the DFT, give back a 0/1
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* decision and a confidence value.
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*/
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int fskdemod_handle(ifax_modp self, void *data, size_t length)
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{
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unsigned char dat[2];
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char *input=data;
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ifax_sint16 *input=data;
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int a1,a2,conf,pwr;
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int handled=0;
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@ -192,6 +262,11 @@ int fskdemod_handle(ifax_modp self, void *data, size_t length)
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return handled;
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}
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/* Constructor. Arguments:
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* int samplerate; - rate at which samples come in
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* int f1,f2; - frequencies that encode 1 and 0
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* int baud; - the baudrate of the transmission. Influences DFT window.
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*/
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int fskdemod_construct(ifax_modp self,va_list args)
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{
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fskdemod_private *priv;
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@ -203,14 +278,15 @@ int fskdemod_construct(ifax_modp self,va_list args)
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self->handle_input =fskdemod_handle;
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self->command =fskdemod_command;
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priv->sps =va_arg(args,int);
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priv->f1 =va_arg(args,int);
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priv->f2 =va_arg(args,int);
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priv->baud=va_arg(args,int);
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sampbaud=(SAMPLES_PER_SECOND+priv->baud)/priv->baud;
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sampbaud=(priv->sps+priv->baud)/priv->baud;
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init_four_help(&priv->freq1,sampbaud,priv->f1);
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init_four_help(&priv->freq2,sampbaud,priv->f2);
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init_four_help(priv,&priv->freq1,sampbaud,priv->f1);
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init_four_help(priv,&priv->freq2,sampbaud,priv->f2);
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return 0;
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}
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