rename util/spkmodem-recv to spkmodem-decode

it's no longer resembling the original util at all,
so a rename seems indicated. yes.

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

3 files changed, 0 insertions, 518 deletions

diff --git a/util/spkmodem_recv/.gitignore b/util/spkmodem_recv/.gitignore
deleted file mode 100644
index 2f5c946c..00000000
--- a/util/spkmodem_recv/.gitignore
+++ /dev/null
@@ -1 +0,0 @@
-spkmodem-recv
diff --git a/util/spkmodem_recv/Makefile b/util/spkmodem_recv/Makefile
deleted file mode 100644
index 293d7475..00000000
--- a/util/spkmodem_recv/Makefile
+++ /dev/null
@@ -1,30 +0,0 @@
-# SPDX-License-Identifier: MIT
-# SPDX-FileCopyrightText: 2022,2026 Leah Rowe <leah@libreboot.org>
-# SPDX-FileCopyrightText: 2023 Riku Viitanen <riku.viitanen@protonmail.com>
-
-CC?=cc
-CFLAGS?=-Os -Wall -Wextra -Werror -pedantic -std=c90
-DESTDIR?=
-PREFIX?=/usr/local
-INSTALL?=install
-
-PROG=spkmodem-recv
-
-all: $(PROG)
-
-$(PROG): spkmodem-recv.c
-	$(CC) $(CFLAGS) spkmodem-recv.c -o $(PROG)
-
-install: $(PROG)
-	mkdir -p $(DESTDIR)$(PREFIX)/bin/
-	install -c $(PROG) $(DESTDIR)$(PREFIX)/bin/
-
-uninstall:
-	rm -f $(DESTDIR)$(PREFIX)/bin/$(PROG)
-
-clean:
-	rm -f $(PROG)
-
-distclean: clean
-
-.PHONY: all install uninstall clean distclean
diff --git a/util/spkmodem_recv/spkmodem-recv.c b/util/spkmodem_recv/spkmodem-recv.c
deleted file mode 100644
index 18e9a738..00000000
--- a/util/spkmodem_recv/spkmodem-recv.c
+++ /dev/null
@@ -1,487 +0,0 @@
-/*
- * SPDX-License-Identifier: GPL-2.0-or-later
- * Copyright (c) 2013 Free Software Foundation, Inc.
- * Copyright (c) 2023, 2026 Leah Rowe <leah@libreboot.org>
- *
- * This program receives text encoded as pulses on the PC speaker,
- * and decodes them via simple FSK (Frequency Shift Keying)
- * demodulation and FIR (Finite Impulse Response) frequency
- * discriminator.
- *
- * It waits for specific tones at specific intervals.
- * It detects tones within the audio stream and reconstructs
- * characters bit-by-bit as the encoded modem signal is received.
- * This is performance-efficient on most CPUs, and has relatively
- * high tolerance for noisy signals (similar to techniques used
- * for data stored on audio cassette tapes).
- *
- * This is a special interface provided by coreboot and GNU GRUB,
- * for computers that lack serial ports (useful for debugging).
- * Note that GRUB and coreboot can both send these signals; this
- * tool merely decodes them. This tool does not *encode*, only
- * decode.
- *
- * Usage example (NOTE: little endian!):
- * parec --channels=1 --rate=48000 --format=s16le | ./spkmodem-recv
- *
- * Originally provided by GNU GRUB, this version is a heavily
- * modified fork that complies with the OpenBSD Kernel Source
- * File Style Guide (KNF) instead of GNU coding standards; it
- * emphasises strict error handling, portability and code
- * quality, as characterised by OpenBSD projects. Several magic
- * numbers have been tidied up, calculated (not hardcoded) and
- * thoroughly explained, unlike in the original version.
- *
- * The original version was essentially a blob, masquerading as
- * source code. This forked source code is therefore the result
- * of extensive reverse engineering (of the GNU source code)!
- * This cleaned up code and extensive commenting will thoroughly
- * explain how the decoding works. This was done as an academic
- * exercise in 2023, continuing in 2026.
- *
- * This fork of spkmodem-recv is provided with Libreboot releases:
- * https://libreboot.org/
- */
-
-#define _POSIX_SOURCE
-
-/*
- * For OpenBSD define, to detect version
- * for deciding whether to use pledge(2)
- */
-#ifdef __OpenBSD__
-#include <sys/param.h>
-#endif
-
-#include <errno.h>
-#include <stdio.h>
-#include <stdarg.h>
-#include <stdlib.h>
-#include <string.h>
-#include <unistd.h>
-
-/*
- * spkmodem is essentially using FSK (Frequency Shift Keying)
- * with two primary tones representing encoded bits,
- * separated by a framing tone.
- * Very cheap on CPU cycles and avoids needing something more
- * expensive like FFT or Goertzel filters, and tolerates
- * weak/noisy signals.
- */
-
-/*
- * Frequency of audio in Hz
- */
-#define SAMPLE_RATE 48000
-
-/*
- * One analysis frame spans 5 ms.
- *
- *   frame_time = SAMPLES_PER_FRAME / SAMPLE_RATE
- *
- * With the default sample rate (48 kHz):
- *
- *   frame_time = N / 48000
- *   0.005 s = N / 48000
- *   N = 0.005 × 48000 = 240 samples
- */
-#define SAMPLES_PER_FRAME 240
-
-/*
- * Number of analysis frames per second.
- *
- * Each increment in the frequency counters corresponds
- * roughly to this many Hertz of tone frequency.
- *
- * With the default values:
- *   FRAME_RATE = 48000 / 240 = 200 Hz
- */
-#define FRAME_RATE ((SAMPLE_RATE) / (SAMPLES_PER_FRAME))
-
-/*
- * Two FIR windows are maintained; one for data tone,
- * and one for the separator tone. They are positioned
- * one frame apart in the ring buffer.
- */
-#define MAX_SAMPLES (2 * (SAMPLES_PER_FRAME))
-
-/*
- * Approx byte offset for ring buffer span, just for
- * easier debug output correlating to the audio stream.
- */
-#define SAMPLE_OFFSET ((MAX_SAMPLES) * (sizeof(short)))
-
-/*
- * Expected tone ranges (approximate, derived from spkmodem).
- * These values are intentionally wide because real-world setups
- * often involve microphones, room acoustics, and cheap ADCs.
- */
-#define SEP_TONE_MIN_HZ 1000
-#define SEP_TONE_MAX_HZ 3000
-
-#define DATA_TONE_MIN_HZ 3000
-#define DATA_TONE_MAX_HZ 12000
-
-/* Mid point used to distinguish the two data tones. */
-#define DATA_TONE_THRESHOLD_HZ 5000
-
-/*
- * Convert tone frequency ranges into pulse counts within the
- * sliding analysis window.
- *
- * pulse_count ≈ tone_frequency / FRAME_RATE
- * where FRAME_RATE = SAMPLE_RATE / SAMPLES_PER_FRAME.
- */
-#define FREQ_SEP_MIN ((SEP_TONE_MIN_HZ) / (FRAME_RATE))
-#define FREQ_SEP_MAX ((SEP_TONE_MAX_HZ) / (FRAME_RATE))
-
-#define FREQ_DATA_MIN ((DATA_TONE_MIN_HZ) / (FRAME_RATE))
-#define FREQ_DATA_MAX ((DATA_TONE_MAX_HZ) / (FRAME_RATE))
-
-#define FREQ_DATA_THRESHOLD ((DATA_TONE_THRESHOLD_HZ) / (FRAME_RATE))
-
-/*
- * Sample amplitude threshold used to convert the waveform
- * into a pulse stream. Values near zero are regarded as noise.
- */
-#define THRESHOLD 500
-
-#define READ_BUF 4096
-
-struct decoder_state {
-	unsigned char pulse[MAX_SAMPLES];
-
-	signed short inbuf[READ_BUF];
-	size_t inpos;
-	size_t inlen;
-
-	int ringpos;
-	int sep_pos;
-
-	/*
-	 * Sliding window pulse counters
-	 * used to detect modem tones
-	 */
-	int freq_data;
-	int freq_separator;
-	int sample_count;
-
-	int ascii_bit;
-	unsigned char ascii;
-
-	int debug;
-	int swap_bytes;
-};
-
-static const char *argv0;
-
-static int host_is_big_endian(void);
-static void handle_audio(struct decoder_state *st);
-static int valid_signal(struct decoder_state *st);
-static void decode_pulse(struct decoder_state *st);
-static signed short read_sample(struct decoder_state *st);
-static int set_ascii_bit(struct decoder_state *st);
-static void print_char(struct decoder_state *st);
-static void print_stats(struct decoder_state *st);
-static void reset_char(struct decoder_state *st);
-
-static void err(int errval, const char *msg, ...);
-static void usage(void);
-static const char *progname(void);
-
-int getopt(int, char * const *, const char *);
-extern char *optarg;
-extern int optind;
-extern int opterr;
-extern int optopt;
-
-int
-main(int argc, char **argv)
-{
-	struct decoder_state st;
-	int c;
-
-#if defined (__OpenBSD__) && defined(OpenBSD)
-#if OpenBSD >= 509
-	if (pledge("stdio", NULL) == -1)
-		err(errno, "pledge");
-#endif
-#endif
-
-	memset(&st, 0, sizeof(st));
-	st.ascii_bit = 7;
-
-	st.ringpos = 0;
-	st.sep_pos = SAMPLES_PER_FRAME;
-
-	argv0 = argv[0];
-
-	while ((c = getopt(argc, argv, "d")) != -1) {
-		if (c != 'd')
-			usage();
-		st.debug = 1;
-		break;
-	}
-
-	if (host_is_big_endian())
-		st.swap_bytes = 1;
-
-	setvbuf(stdout, NULL, _IONBF, 0);
-
-	for (;;)
-		handle_audio(&st);
-
-	return EXIT_SUCCESS;
-}
-
-static int
-host_is_big_endian(void)
-{
-	unsigned int x = 1;
-	return (*(unsigned char *)&x == 0);
-}
-
-static void
-handle_audio(struct decoder_state *st)
-{
-	int sample;
-
-	/*
-	 * If the modem signal disappears for several frames,
-	 * discard the partially assembled character.
-	 */
-	if (st->sample_count > (3 * SAMPLES_PER_FRAME))
-		reset_char(st);
-	if (!valid_signal(st)) {
-		decode_pulse(st);
-		return;
-	}
-
-	if (set_ascii_bit(st) < 0)
-		print_char(st);
-
-	st->sample_count = 0;
-	for (sample = 0; sample < SAMPLES_PER_FRAME; sample++)
-		decode_pulse(st);
-}
-
-/*
- * Verify that the observed pulse densities fall within the
- * expected ranges for spkmodem tones. This prevents random noise
- * from being misinterpreted as data.
- */
-static int
-valid_signal(struct decoder_state *st)
-{
-	return (st->freq_separator > FREQ_SEP_MIN &&
-	    st->freq_separator < FREQ_SEP_MAX &&
-	    st->freq_data > FREQ_DATA_MIN &&
-	    st->freq_data < FREQ_DATA_MAX);
-}
-
-/*
- * Main demodulation step (moving-sum FIR filter).
- */
-static void
-decode_pulse(struct decoder_state *st)
-{
-	unsigned char old_ring, old_sep;
-	unsigned char new_pulse;
-	int ringpos;
-	int sep_pos;
-	signed short sample;
-
-	ringpos = st->ringpos;
-	sep_pos = st->sep_pos;
-
-	/*
-	 * Sliding rectangular FIR (Finite Impulse Response) filter.
-	 *
-	 * After thresholding, the signal becomes a stream of 0/1 pulses.
-	 * The decoder measures pulse density over two windows:
-	 *
-	 * freq_data: pulses in the "data" window
-	 * freq_separator: pulses in the "separator" window
-	 *
-	 * Instead of calculating each window every time (O(N) per frame), we
-	 * update the window sums incrementally:
-	 *
-	 *   sum_new = sum_old - pulse_leaving + pulse_entering
-	 *
-	 * This keeps the filter O(1) per sample instead of O(N).
-	 * The technique is equivalent to a rectangular FIR filter
-	 * implemented as a sliding moving sum.
-	 *
-	 * The two windows are exactly SAMPLES_PER_FRAME apart in the ring
-	 * buffer, so the pulse leaving the data window is simultaneously
-	 * entering the separator window.
-	 */
-	old_ring = st->pulse[ringpos];
-	old_sep  = st->pulse[sep_pos];
-	st->freq_data -= old_ring;
-	st->freq_data += old_sep;
-	st->freq_separator -= old_sep;
-
-	sample = read_sample(st);
-
-	/*
-	 * Convert the waveform sample into a pulse (0 or 1).
-	 *
-	 * The unsigned comparison creates a small dead zone near zero,
-	 * suppressing small amplitude noise from microphones or
-	 * cheap ADCs. Real PC speaker tones are far outside this
-	 * range, so they still produce clean pulses.
-	 */
-	if ((unsigned)(sample + THRESHOLD)
-	    > (unsigned)(2 * THRESHOLD))
-		new_pulse = 1;
-	else
-		new_pulse = 0;
-
-	st->pulse[ringpos] = new_pulse;
-	st->freq_separator += new_pulse;
-
-	/*
-	 * Advance both FIR windows through the ring buffer.
-	 * The separator window always stays one frame ahead
-	 * of the data window.
-	 */
-	ringpos++;
-	if (ringpos >= MAX_SAMPLES)
-		ringpos = 0;
-	sep_pos++;
-	if (sep_pos >= MAX_SAMPLES)
-		sep_pos = 0;
-
-	st->ringpos = ringpos;
-	st->sep_pos = sep_pos;
-
-	st->sample_count++;
-}
-
-static signed short
-read_sample(struct decoder_state *st)
-{
-	size_t n;
-	signed short sample;
-	unsigned short u;
-
-	while (st->inpos >= st->inlen) {
-
-		n = fread(st->inbuf, sizeof(st->inbuf[0]),
-		    READ_BUF, stdin);
-
-		if (n == 0) {
-			if (ferror(stdin))
-				err(errno, "stdin read");
-			if (feof(stdin))
-				exit(EXIT_SUCCESS);
-		}
-
-		st->inpos = 0;
-		st->inlen = n;
-	}
-
-	sample = st->inbuf[st->inpos++];
-
-	if (st->swap_bytes) {
-		u = (unsigned short)sample;
-		u = (u >> 8) | (u << 8);
-
-		sample = (signed short)u;
-	}
-
-	return sample;
-}
-
-/*
- * Each validated frame contributes one bit of modem data.
- * Bits are accumulated MSB-first into the ASCII byte.
- */
-static int
-set_ascii_bit(struct decoder_state *st)
-{
-	if (st->debug)
-		print_stats(st);
-	if (st->freq_data < FREQ_DATA_THRESHOLD)
-		st->ascii |= (1 << st->ascii_bit);
-
-	st->ascii_bit--;
-	return st->ascii_bit;
-}
-
-static void
-print_char(struct decoder_state *st)
-{
-	if (st->debug)
-		printf("<%c,%x>", st->ascii, st->ascii);
-	else
-		putchar(st->ascii);
-
-	reset_char(st);
-}
-
-static void
-print_stats(struct decoder_state *st)
-{
-	long pos;
-
-	if ((pos = ftell(stdin)) == -1) {
-		printf("%d %d %d\n",
-		    st->freq_data,
-		    st->freq_separator,
-		    FREQ_DATA_THRESHOLD);
-		return;
-	}
-
-	printf("%d %d %d @%ld\n",
-	    st->freq_data,
-	    st->freq_separator,
-	    FREQ_DATA_THRESHOLD,
-	    pos - SAMPLE_OFFSET);
-}
-
-static void
-reset_char(struct decoder_state *st)
-{
-	st->ascii = 0;
-	st->ascii_bit = 7;
-}
-
-static void
-err(int errval, const char *msg, ...)
-{
-	va_list ap;
-
-	fprintf(stderr, "%s: ", progname());
-
-	va_start(ap, msg);
-	vfprintf(stderr, msg, ap);
-	va_end(ap);
-
-	fprintf(stderr, ": %s\n", strerror(errval));
-	exit(EXIT_FAILURE);
-}
-
-static void
-usage(void)
-{
-	fprintf(stderr, "usage: %s [-d]\n", progname());
-	exit(EXIT_FAILURE);
-}
-
-static const char *
-progname(void)
-{
-	const char *p;
-
-	if (argv0 == NULL || *argv0 == '\0')
-		return "";
-
-	p = strrchr(argv0, '/');
-
-	if (p)
-		return p + 1;
-	else
-		return argv0;
-}