kopia lustrzana https://github.com/windytan/slowrx
111 wiersze
2.7 KiB
C
111 wiersze
2.7 KiB
C
#include <stdlib.h>
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#include <math.h>
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#include <gtk/gtk.h>
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#include <alsa/asoundlib.h>
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#include <fftw3.h>
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#include "common.h"
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/*
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*
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* Decode FSK ID
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*
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* * The FSK IDs are 6-bit bytes, LSB first, 45.45 baud (22 ms/bit), 1900 Hz = 1, 2100 Hz = 0
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* * Text data starts with 20 2A and ends in 01
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* * Add 0x20 and the data becomes ASCII
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*
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*/
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void GetFSK (char *dest) {
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guint FFTLen = 2048, i=0, LoBin, HiBin, MidBin, TestNum=0, TestPtr=0;
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guchar Bit = 0, AsciiByte = 0, BytePtr = 0, TestBits[24] = {0}, BitPtr=0;
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double HiPow,LoPow,Hann[970];
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gboolean InSync = FALSE;
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// Bit-reversion lookup table
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static const guchar BitRev[] = {
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0x00, 0x20, 0x10, 0x30, 0x08, 0x28, 0x18, 0x38,
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0x04, 0x24, 0x14, 0x34, 0x0c, 0x2c, 0x1c, 0x3c,
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0x02, 0x22, 0x12, 0x32, 0x0a, 0x2a, 0x1a, 0x3a,
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0x06, 0x26, 0x16, 0x36, 0x0e, 0x2e, 0x1e, 0x3e,
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0x01, 0x21, 0x11, 0x31, 0x09, 0x29, 0x19, 0x39,
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0x05, 0x25, 0x15, 0x35, 0x0d, 0x2d, 0x1d, 0x3d,
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0x03, 0x23, 0x13, 0x33, 0x0b, 0x2b, 0x1b, 0x3b,
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0x07, 0x27, 0x17, 0x37, 0x0f, 0x2f, 0x1f, 0x3f };
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for (i = 0; i < FFTLen; i++) fft.in[i] = 0;
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// Create 22ms Hann window
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for (i = 0; i < 970; i++) Hann[i] = 0.5 * (1 - cos( 2 * M_PI * i / 969.0 ) );
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while ( TRUE ) {
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// Read data from DSP
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readPcm(InSync ? 970: 485);
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if (pcm.WindowPtr < 485) {
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pcm.WindowPtr += (InSync ? 970 : 485);
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continue;
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}
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// Apply Hann window
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for (i = 0; i < 970; i++) fft.in[i] = pcm.Buffer[pcm.WindowPtr+i- 485] * Hann[i];
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pcm.WindowPtr += (InSync ? 970 : 485);
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// FFT of last 22 ms
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fftw_execute(fft.Plan2048);
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LoBin = GetBin(1900+CurrentPic.HedrShift, FFTLen)-1;
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MidBin = GetBin(2000+CurrentPic.HedrShift, FFTLen);
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HiBin = GetBin(2100+CurrentPic.HedrShift, FFTLen)+1;
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LoPow = 0;
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HiPow = 0;
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for (i = LoBin; i <= HiBin; i++) {
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if (i < MidBin) LoPow += power(fft.out[i]);
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else HiPow += power(fft.out[i]);
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}
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Bit = (LoPow>HiPow);
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if (!InSync) {
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// Wait for 20 2A
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TestBits[TestPtr % 24] = Bit;
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TestNum = 0;
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for (i=0; i<12; i++) TestNum |= TestBits[(TestPtr - (23-i*2)) % 24] << (11-i);
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if (BitRev[(TestNum >> 6) & 0x3f] == 0x20 && BitRev[TestNum & 0x3f] == 0x2a) {
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InSync = TRUE;
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AsciiByte = 0;
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BitPtr = 0;
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BytePtr = 0;
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}
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if (++TestPtr > 200) break;
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} else {
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AsciiByte |= Bit << BitPtr;
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if (++BitPtr == 6) {
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if (AsciiByte < 0x0d || BytePtr > 9) break;
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dest[BytePtr] = AsciiByte + 0x20;
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BitPtr = 0;
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AsciiByte = 0;
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BytePtr ++;
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}
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}
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}
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dest[BytePtr] = '\0';
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}
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