util/spkmodem_recv: Import from coreboot

Imported from util/spkmodem_recv at coreboot
revision:

e70bc423f9a2e1d13827f2703efe1f9c72549f20

This is a client for spkmodem, to allow serial
console via PC speaker.

I've decided to import it in lbmk, because I
heavily modified it. The patches will be
applied next.

Signed-off-by: Leah Rowe <leah@libreboot.org>

util/spkmodem_recv/.gitignore

+spkmodem-recv

util/spkmodem_recv/Makefile

+# 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/

util/spkmodem_recv/annotation

+/* 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 */
+
+// 1/48000Hz * 240 = 5ms,
+#define SAMPLES_PER_TRAME 240
+// 5 transitions = 2.5 pulses/5ms = 500Hz
+#define FREQ_SEP_MIN 5
+// 15 transitions = 7.5 pulses/5ms = 1500Hz
+#define FREQ_SEP_MAX 15
+// 15 transitions = 7.5 pulses/5ms = 1500Hz
+#define FREQ_DATA_MIN 15
+// 25 transitions = 12.5 pulses/5ms = 2500Hz
+#define FREQ_DATA_THRESHOLD 25
+// 60 transitions = 30 pulses/5ms = 6000Hz
+#define FREQ_DATA_MAX 60
+// Threshold amplitude to register a transition
+#define THRESHOLD 500
+
+#define DEBUG 0
+#define FLUSH_TIMEOUT 1
+
+// Just a ring buffer of the raw samples, not meaningfully
+// used otherwise
+static signed short trame[2 * SAMPLES_PER_TRAME];
+// stores a 1 for each detected edge transition of the audio signal,
+// 0 otherwise
+static signed short pulse[2 * SAMPLES_PER_TRAME];
+// ring buffer index
+static int ringpos = 0;
+// pos is the polarity to look for in the next sample
+// f1 counts the number of transitions in each trame
+// f2  
+static int pos, f1, f2;
+// amplitude not meaningfully used
+static int amplitude = 0;
+static int lp = 0;
+
+static void read_sample (void)
+{
+    amplitude -= abs (trame[ringpos]);
+    f1 -= pulse[ringpos];
+    // ringpos + SAMPLES_PER_TRAME will be the results of the
+    // previous trame interval
+    f1 += pulse[(ringpos + SAMPLES_PER_TRAME) % (2 * SAMPLES_PER_TRAME)];
+    // gradually clear the count of pulses from the previous trame from f1
+    f2 -= pulse[(ringpos + SAMPLES_PER_TRAME) % (2 * SAMPLES_PER_TRAME)];
+    // Read one 16 bit sample to trame index ringpos
+    fread (trame + ringpos, 1, sizeof (trame[0]), stdin);
+    // amplitude will be the difference in magnitude of old value
+    // in trame and new value
+    amplitude += abs (trame[ringpos]);
+    
+    // if magnitude of trame[ringpos] greater than threshold, set pulse to 1
+    // found positive peak, now look for negative peak
+    if (pos ? (trame[ringpos] < -THRESHOLD) : (trame[ringpos] > +THRESHOLD)) {
+        pulse[ringpos] = 1;
+        // Invert sign flag
+        pos = !pos;
+        f2++;
+    } else {
+        pulse[ringpos] = 0;
+    }
+    // move buffer index forward
+    ringpos++;
+    ringpos %= 2 * SAMPLES_PER_TRAME;
+    lp++;
+}
+
+int main ()
+{
+    int bitn = 7;
+    char c = 0;
+    int i;
+    int llp = 0;
+    while (!feof (stdin)) {
+        // lp gets reset whenever a valid bit is detected,
+        // reset things if a bit hasn't been read in a while
+        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;
+}

util/spkmodem_recv/description.md

+Decode spkmodem signals `C`

util/spkmodem_recv/spkmodem-recv.c

+/* 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;
+}