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-rw-r--r--util/spkmodem_recv/.gitignore1
-rw-r--r--util/spkmodem_recv/Makefile9
-rw-r--r--util/spkmodem_recv/description.md1
-rw-r--r--util/spkmodem_recv/spkmodem-recv.c100
4 files changed, 111 insertions, 0 deletions
diff --git a/util/spkmodem_recv/.gitignore b/util/spkmodem_recv/.gitignore
new file mode 100644
index 00000000..2f5c946c
--- /dev/null
+++ b/util/spkmodem_recv/.gitignore
@@ -0,0 +1 @@
+spkmodem-recv
diff --git a/util/spkmodem_recv/Makefile b/util/spkmodem_recv/Makefile
new file mode 100644
index 00000000..92a3bfe9
--- /dev/null
+++ b/util/spkmodem_recv/Makefile
@@ -0,0 +1,9 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+PREFIX ?= /usr/local
+INSTALL ?= install
+
+spkmodem-recv:
+ $(CC) -o $@ $@.c
+install: spkmodem-recv
+ $(INSTALL) -d $(DESTDIR)$(PREFIX)/bin/
+ $(INSTALL) $< -t $(DESTDIR)$(PREFIX)/bin/
diff --git a/util/spkmodem_recv/description.md b/util/spkmodem_recv/description.md
new file mode 100644
index 00000000..fe62f169
--- /dev/null
+++ b/util/spkmodem_recv/description.md
@@ -0,0 +1 @@
+Decode spkmodem signals `C`
diff --git a/util/spkmodem_recv/spkmodem-recv.c b/util/spkmodem_recv/spkmodem-recv.c
new file mode 100644
index 00000000..cd7bd483
--- /dev/null
+++ b/util/spkmodem_recv/spkmodem-recv.c
@@ -0,0 +1,100 @@
+/* spkmodem-recv.c - decode spkmodem signals */
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+/* Compilation: gcc -o spkmodem-recv spkmodem-recv */
+/* Usage: parec --channels=1 --rate=48000 --format=s16le | ./spkmodem-recv */
+
+#define SAMPLES_PER_TRAME 240
+#define FREQ_SEP_MIN 5
+#define FREQ_SEP_MAX 15
+#define FREQ_DATA_MIN 15
+#define FREQ_DATA_THRESHOLD 25
+#define FREQ_DATA_MAX 60
+#define THRESHOLD 500
+
+#define DEBUG 0
+#define FLUSH_TIMEOUT 1
+
+static signed short trame[2 * SAMPLES_PER_TRAME];
+static signed short pulse[2 * SAMPLES_PER_TRAME];
+static int ringpos = 0;
+static int pos, f1, f2;
+static int amplitude = 0;
+static int lp = 0;
+
+static void
+read_sample (void)
+{
+ amplitude -= abs (trame[ringpos]);
+ f1 -= pulse[ringpos];
+ f1 += pulse[(ringpos + SAMPLES_PER_TRAME) % (2 * SAMPLES_PER_TRAME)];
+ f2 -= pulse[(ringpos + SAMPLES_PER_TRAME) % (2 * SAMPLES_PER_TRAME)];
+ fread (trame + ringpos, 1, sizeof (trame[0]), stdin);
+ amplitude += abs (trame[ringpos]);
+
+ if (pos ? (trame[ringpos] < -THRESHOLD)
+ : (trame[ringpos] > +THRESHOLD))
+ {
+ pulse[ringpos] = 1;
+ pos = !pos;
+ f2++;
+ }
+ else
+ pulse[ringpos] = 0;
+ ringpos++;
+ ringpos %= 2 * SAMPLES_PER_TRAME;
+ lp++;
+}
+
+int
+main ()
+{
+ int bitn = 7;
+ char c = 0;
+ int i;
+ int llp = 0;
+ while (!feof (stdin))
+ {
+ if (lp > 3 * SAMPLES_PER_TRAME)
+ {
+ bitn = 7;
+ c = 0;
+ lp = 0;
+ llp++;
+ }
+ if (llp == FLUSH_TIMEOUT)
+ fflush (stdout);
+ if (f2 > FREQ_SEP_MIN && f2 < FREQ_SEP_MAX
+ && f1 > FREQ_DATA_MIN && f1 < FREQ_DATA_MAX)
+ {
+#if DEBUG
+ printf ("%d %d %d @%d\n", f1, f2, FREQ_DATA_THRESHOLD,
+ ftell (stdin) - sizeof (trame));
+#endif
+ if (f1 < FREQ_DATA_THRESHOLD)
+ c |= (1 << bitn);
+ bitn--;
+ if (bitn < 0)
+ {
+#if DEBUG
+ printf ("<%c, %x>", c, c);
+#else
+ printf ("%c", c);
+#endif
+ bitn = 7;
+ c = 0;
+ }
+ lp = 0;
+ llp = 0;
+ for (i = 0; i < SAMPLES_PER_TRAME; i++)
+ read_sample ();
+ continue;
+ }
+ read_sample ();
+ }
+ return 0;
+}