mirror of
https://git.proxmox.com/git/grub2
synced 2025-05-17 09:51:32 +00:00
99 lines
1.9 KiB
C
99 lines
1.9 KiB
C
#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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/* Compilation: gcc -o spkmodem-recv spkmodem-recv */
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/* Usage: parecord --channels=1 --rate=48000 --format=s16le | ./spkmodem-recv */
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#define RATE 48000
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#define SAMPLES_PER_TRAME 480
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#define AMPLITUDE_THRESHOLD 100000
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#define FREQ_SEP_MIN 15
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#define FREQ_SEP_NOM 20
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#define FREQ_SEP_MAX 25
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#define FREQ_DATA_MIN 10
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#define FREQ_DATA_THRESHOLD 60
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#define FREQ_DATA_MAX 120
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#define AMPLITUDE_SAMPLES 2 * SAMPLES_PER_TRAME
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#define THRESHOLD 1000
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#define DEBUG 0
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static signed short trame[2 * SAMPLES_PER_TRAME];
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static signed short pulse[2 * SAMPLES_PER_TRAME];
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static int ringpos = 0;
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static int pos, f1, f2;
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static int amplitude = 0;
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static int lp = 0;
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static void
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read_sample (void)
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{
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amplitude -= abs (trame[ringpos]);
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f1 -= pulse[ringpos];
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f1 += pulse[(ringpos + SAMPLES_PER_TRAME) % (2 * SAMPLES_PER_TRAME)];
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f2 -= pulse[(ringpos + SAMPLES_PER_TRAME) % (2 * SAMPLES_PER_TRAME)];
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fread (trame + ringpos, 1, sizeof (trame[0]), stdin);
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amplitude += abs (trame[ringpos]);
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if (pos ? (trame[ringpos] < -THRESHOLD)
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: (trame[ringpos] > +THRESHOLD))
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{
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pulse[ringpos] = 1;
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pos = !pos;
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f2++;
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}
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else
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pulse[ringpos] = 0;
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ringpos++;
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ringpos %= 2 * SAMPLES_PER_TRAME;
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lp++;
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}
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int
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main ()
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{
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int bitn = 7;
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char c = 0;
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int i;
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while (!feof (stdin))
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{
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if (lp > 20000)
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{
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fflush (stdout);
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bitn = 7;
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c = 0;
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lp = 0;
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}
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if (f2 > 12 && f2 < 25
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&& f1 > 5 && f1 < 120)
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{
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#if DEBUG
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printf ("%d %d %d @%d\n", f1, f2, FREQ_DATA_THRESHOLD,
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ftell (stdin) - sizeof (trame));
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#endif
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if (f1 < 60)
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c |= (1 << bitn);
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bitn--;
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if (bitn < 0)
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{
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#if DEBUG
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printf ("<%c, %x>", c, c);
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#else
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printf ("%c", c);
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#endif
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bitn = 7;
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c = 0;
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}
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lp = 0;
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for (i = 0; i < SAMPLES_PER_TRAME; i++)
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read_sample ();
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continue;
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}
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read_sample ();
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}
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return 0;
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}
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