switch spkmodem_decode back to spkmodem_recv

this version is more tested. i'll merge _decode back
once it's better tested. it contains a lot of invasive
changes, whereas recv is much closer to the original GNU
code that i inherited, that i also know works quite well.

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

util/spkmodem_recv/.gitignore

@@ -0,0 +1 @@
+spkmodem-recv

util/spkmodem_recv/Makefile

@@ -0,0 +1,14 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+CC?=cc
+CFLAGS?=-Os -Wall -Wextra -Werror -pedantic
+DESTDIR?=
+PREFIX?=/usr/local
+INSTALL?=install
+
+spkmodem-recv:
+	$(CC) $(CFLAGS) -o $@ $@.c
+install: spkmodem-recv
+	$(INSTALL) -d $(DESTDIR)$(PREFIX)/bin/
+	$(INSTALL) $< -t $(DESTDIR)$(PREFIX)/bin/
+clean:
+	rm -f spkmodem-recv

util/spkmodem_recv/spkmodem-recv.c

@@ -0,0 +1,124 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* SPDX-FileCopyrightText: 2013 Free Software Foundation, Inc. */
+/* Usage: parec --channels=1 --rate=48000 --format=s16le | ./spkmodem-recv */
+
+/* Forked from coreboot's version, at util/spkmodem_recv/ in coreboot.git,
+ * revision 5c2b5fcf2f9c9259938fd03cfa3ea06b36a007f0 as of 3 January 2022.
+ * This version is heavily modified, re-written based on OpenBSD Kernel Source
+ * File Style Guide (KNF); this change is Copyright 2023 Leah Rowe. */
+
+#include <err.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#define SAMPLES_PER_FRAME 240
+#define MAX_SAMPLES (2 * SAMPLES_PER_FRAME)
+#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 ERR() (errno = errno ? errno : ECANCELED)
+#define reset_char() ascii = 0, ascii_bit = 7
+
+signed short frame[MAX_SAMPLES], pulse[MAX_SAMPLES];
+int ringpos, debug, freq_data, freq_separator, sample_count, ascii_bit = 7;
+char ascii = 0;
+
+void handle_audio(void);
+void decode_pulse(void);
+int set_ascii_bit(void);
+void print_char(void);
+void print_stats(void);
+
+int
+main(int argc, char *argv[])
+{
+	int c;
+#ifdef __OpenBSD__
+	if (pledge("stdio", NULL) == -1)
+		err(ERR(), "pledge");
+#endif
+	while ((c = getopt(argc, argv, "d")) != -1)
+		if (!(debug = (c == 'd')))
+			err(errno = EINVAL, NULL);
+	setvbuf(stdout, NULL, _IONBF, 0);
+	while (!feof(stdin))
+		handle_audio();
+	if (errno && debug)
+		err(errno, "Unhandled error, errno %d", errno);
+	return errno;
+}
+
+void
+handle_audio(void)
+{
+	if (sample_count > (3 * SAMPLES_PER_FRAME))
+		sample_count = reset_char();
+	if ((freq_separator <= FREQ_SEP_MIN) || (freq_separator >= FREQ_SEP_MAX)
+	    || (freq_data <= FREQ_DATA_MIN) || (freq_data >= FREQ_DATA_MAX)) {
+		decode_pulse();
+		return;
+	}
+
+	if (set_ascii_bit() < 0)
+		print_char();
+	sample_count = 0;
+	for (int sample = 0; sample < SAMPLES_PER_FRAME; sample++)
+		decode_pulse();
+}
+
+void
+decode_pulse(void)
+{
+	int next_ringpos = (ringpos + SAMPLES_PER_FRAME) % MAX_SAMPLES;
+	freq_data -= pulse[ringpos];
+	freq_data += pulse[next_ringpos];
+	freq_separator -= pulse[next_ringpos];
+
+	fread(frame + ringpos, 1, sizeof(frame[0]), stdin);
+	if (ferror(stdin) != 0)
+		err(ERR(), "Could not read from frame.");
+
+	if ((pulse[ringpos] = (abs(frame[ringpos]) > THRESHOLD) ? 1 : 0))
+		++freq_separator;
+	++ringpos;
+	ringpos %= MAX_SAMPLES;
+	++sample_count;
+}
+
+int
+set_ascii_bit(void)
+{
+	if (debug)
+		print_stats();
+	if (freq_data < FREQ_DATA_THRESHOLD)
+		ascii |= (1 << ascii_bit);
+	--ascii_bit;
+	return ascii_bit;
+}
+
+void
+print_char(void)
+{
+	if (debug)
+		printf("<%c, %x>", ascii, ascii);
+	else
+		printf("%c", ascii);
+	reset_char();
+}
+
+void
+print_stats(void)
+{
+	long stdin_pos;
+	if ((stdin_pos = ftell(stdin)) == -1)
+		err(ERR(), NULL);
+	printf ("%d %d %d @%ld\n", freq_data, freq_separator,
+	    FREQ_DATA_THRESHOLD, stdin_pos - sizeof(frame));
+}