mirror of
https://codeberg.org/libreboot/lbmk.git
synced 2026-07-11 05:52:36 +02:00
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>
This commit is contained in:
Leah Rowe
@@ -1,2 +0,0 @@
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spkmodem-recv
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spkmodem-decode
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@@ -1,30 +0,0 @@
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# SPDX-License-Identifier: MIT
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# SPDX-FileCopyrightText: 2022,2026 Leah Rowe <leah@libreboot.org>
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# SPDX-FileCopyrightText: 2023 Riku Viitanen <riku.viitanen@protonmail.com>
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CC?=cc
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CFLAGS?=-Os -Wall -Wextra -Werror -pedantic -std=c90
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DESTDIR?=
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PREFIX?=/usr/local
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INSTALL?=install
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PROG=spkmodem-decode
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all: $(PROG)
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$(PROG): spkmodem-decode.c
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$(CC) $(CFLAGS) spkmodem-decode.c -o $(PROG)
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install: $(PROG)
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mkdir -p $(DESTDIR)$(PREFIX)/bin/
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install -c $(PROG) $(DESTDIR)$(PREFIX)/bin/
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uninstall:
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rm -f $(DESTDIR)$(PREFIX)/bin/$(PROG)
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clean:
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rm -f $(PROG)
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distclean: clean
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.PHONY: all install uninstall clean distclean
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@@ -1,725 +0,0 @@
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/*
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* SPDX-License-Identifier: GPL-2.0-or-later
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* Copyright (c) 2013 Free Software Foundation, Inc.
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* Copyright (c) 2023, 2026 Leah Rowe <leah@libreboot.org>
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*
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* This program receives text encoded as pulses on the PC speaker,
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* and decodes them via simple FSK (Frequency Shift Keying)
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* demodulation and FIR (Finite Impulse Response) frequency
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* discriminator.
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*
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* It waits for specific tones at specific intervals.
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* It detects tones within the audio stream and reconstructs
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* characters bit-by-bit as the encoded modem signal is received.
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* This is performance-efficient on most CPUs, and has relatively
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* high tolerance for noisy signals (similar to techniques used
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* for data stored on audio cassette tapes).
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*
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* This is a special interface provided by coreboot and GNU GRUB,
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* for computers that lack serial ports (useful for debugging).
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* Note that GRUB and coreboot can both send these signals; this
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* tool merely decodes them. This tool does not *encode*, only
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* decode.
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*
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* Usage example (NOTE: little endian!):
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* parec --channels=1 --rate=48000 --format=s16le | ./spkmodem-decode
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*
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* Originally provided by GNU GRUB, this version is a heavily
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* modified fork that complies with the OpenBSD Kernel Source
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* File Style Guide (KNF) instead of GNU coding standards; it
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* emphasises strict error handling, portability and code
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* quality, as characterised by OpenBSD projects. Several magic
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* numbers have been tidied up, calculated (not hardcoded) and
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* thoroughly explained, unlike in the original version.
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*
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* The original version was essentially a blob, masquerading as
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* source code. This forked source code is therefore the result
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* of extensive reverse engineering (of the GNU source code)!
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* This cleaned up code and extensive commenting will thoroughly
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* explain how the decoding works. This was done as an academic
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* exercise in 2023, continuing in 2026.
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*
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* This fork of spkmodem-recv, called spkmodem-decode, is provided
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* with Libreboot releases:
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* https://libreboot.org/
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*
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* The original GNU version is here, if you're morbidly curious:
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* https://cgit.git.savannah.gnu.org/cgit/grub.git/plain/util/spkmodem-recv.c?id=3dce38eb196f47bdf86ab028de74be40e13f19fd
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*
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* Libreboot's version was renamed to spkmodem-decode on 12 March 2026,
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* since Libreboot's version no longer closely resembles the GNU
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* version at all; ergo, a full rename was in order. GNU's version
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* was called spkmodem-recv.
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*/
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#define _POSIX_SOURCE
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/*
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* For OpenBSD define, to detect version
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* for deciding whether to use pledge(2)
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*/
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#ifdef __OpenBSD__
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#include <sys/param.h>
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#endif
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#include <errno.h>
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#include <limits.h>
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#include <stdio.h>
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#include <stdarg.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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/*
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* spkmodem is essentially using FSK (Frequency Shift Keying)
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* with two primary tones representing encoded bits,
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* separated by a framing tone.
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* Very cheap on CPU cycles and avoids needing something more
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* expensive like FFT or Goertzel filters, and tolerates
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* weak/noisy signals.
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*/
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/*
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* Frequency of audio in Hz
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* WARNING: if changing, make sure to adjust
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* SAMPLES_PER_FRAME accordingly (see maths below)
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*/
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#define SAMPLE_RATE 48000
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/*
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* One analysis frame spans 5 ms.
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*
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* frame_time = SAMPLES_PER_FRAME / SAMPLE_RATE
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*
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* With the default sample rate (48 kHz):
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*
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* frame_time = N / 48000
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* 0.005 s = N / 48000
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* N = 0.005 × 48000 = 240 samples
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*/
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#define SAMPLES_PER_FRAME 240
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/*
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* Number of analysis frames per second.
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*
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* Each increment in the frequency counters corresponds
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* roughly to this many Hertz of tone frequency.
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*
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* With the default values:
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* FRAME_RATE = 48000 / 240 = 200 Hz
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*/
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#define FRAME_RATE ((SAMPLE_RATE) / (SAMPLES_PER_FRAME))
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/*
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* Two FIR windows are maintained; one for data tone,
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* and one for the separator tone. They are positioned
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* one frame apart in the ring buffer.
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*/
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#define MAX_SAMPLES (2 * (SAMPLES_PER_FRAME))
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/*
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* Approx byte offset for ring buffer span, just for
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* easier debug output correlating to the audio stream.
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*/
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#define SAMPLE_OFFSET ((MAX_SAMPLES) * (sizeof(short)))
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/*
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* Expected tone ranges (approximate, derived from spkmodem).
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* These values are intentionally wide because real-world setups
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* often involve microphones, room acoustics, and cheap ADCs.
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*/
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#define SEP_TONE_MIN_HZ 1000
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#define SEP_TONE_MAX_HZ 3000
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#define SEP_TOLERANCE_PULSES \
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(((SEP_TONE_MAX_HZ) - (SEP_TONE_MIN_HZ)) / (2 * (FRAME_RATE)))
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#define DATA_TONE_MIN_HZ 3000
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#define DATA_TONE_MAX_HZ 12000
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/* Mid point used to distinguish the two data tones. */
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#define DATA_TONE_THRESHOLD_HZ 5000
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/*
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* Convert tone frequency ranges into pulse counts within the
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* sliding analysis window.
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*
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* pulse_count = tone_frequency / FRAME_RATE
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* where FRAME_RATE = SAMPLE_RATE / SAMPLES_PER_FRAME.
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*/
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#define FREQ_SEP_MIN ((SEP_TONE_MIN_HZ) / (FRAME_RATE))
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#define FREQ_SEP_MAX ((SEP_TONE_MAX_HZ) / (FRAME_RATE))
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#define FREQ_DATA_MIN ((DATA_TONE_MIN_HZ) / (FRAME_RATE))
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#define FREQ_DATA_MAX ((DATA_TONE_MAX_HZ) / (FRAME_RATE))
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#define FREQ_DATA_THRESHOLD ((DATA_TONE_THRESHOLD_HZ) / (FRAME_RATE))
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/*
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* These determine how long the program will wait during
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* tone auto-detection, before shifting to defaults.
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* It is done every LEARN_FRAMES number of frames.
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*/
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#define LEARN_SECONDS 1
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#define LEARN_FRAMES ((LEARN_SECONDS) * (FRAME_RATE))
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/*
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* Sample amplitude threshold used to convert the waveform
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* into a pulse stream. Values near zero are regarded as noise.
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*/
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#define THRESHOLD 500
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#define READ_BUF 4096
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struct decoder_state {
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unsigned char pulse[MAX_SAMPLES];
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signed short inbuf[READ_BUF];
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size_t inpos;
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size_t inlen;
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int ringpos;
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int sep_pos;
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/*
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* Sliding window pulse counters
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* used to detect modem tones
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*/
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int freq_data;
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int freq_separator;
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int sample_count;
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int ascii_bit;
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unsigned char ascii;
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int debug;
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int swap_bytes;
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/* dynamic separator calibration */
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int sep_sum;
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int sep_samples;
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int sep_min;
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int sep_max;
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/* for automatic tone detection */
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int freq_min;
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int freq_max;
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int freq_threshold;
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int learn_frames;
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/* previous sample used for edge detection */
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signed short prev_sample;
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};
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static const char *argv0;
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/*
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* 16-bit little endian words are read
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* continuously. we will swap them, if
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* the host cpu is big endian.
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*/
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static int host_is_big_endian(void);
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/* main loop */
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static void handle_audio(struct decoder_state *st);
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/* separate tone tolerances */
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static void select_separator_tone(struct decoder_state *st);
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static int is_valid_signal(struct decoder_state *st);
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/* output to terminal */
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static int set_ascii_bit(struct decoder_state *st);
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static void print_char(struct decoder_state *st);
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static void reset_char(struct decoder_state *st);
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/* process samples/frames */
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static void decode_pulse(struct decoder_state *st);
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static signed short read_sample(struct decoder_state *st);
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static void read_words(struct decoder_state *st);
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/* continually adjust tone */
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static void detect_tone(struct decoder_state *st);
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static int silent_signal(struct decoder_state *st);
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static void select_low_tone(struct decoder_state *st);
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/* debug */
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static void print_stats(struct decoder_state *st);
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/* error handling / usage */
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static void err(int errval, const char *msg, ...);
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static void usage(void);
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static const char *progname(void);
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/* portability (old systems) */
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int getopt(int, char * const *, const char *);
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extern char *optarg;
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extern int optind;
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extern int opterr;
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extern int optopt;
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#ifndef CHAR_BIT
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#define CHAR_BIT 8
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#endif
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typedef char static_assert_char_is_8_bits[(CHAR_BIT == 8) ? 1 : -1];
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typedef char static_assert_char_is_1[(sizeof(char) == 1) ? 1 : -1];
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typedef char static_assert_short[(sizeof(short) == 2) ? 1 : -1];
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typedef char static_assert_int_is_4[(sizeof(int) >= 4) ? 1 : -1];
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typedef char static_assert_twos_complement[
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((-1 & 3) == 3) ? 1 : -1
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];
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int
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main(int argc, char **argv)
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{
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struct decoder_state st;
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int c;
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argv0 = argv[0];
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#if defined (__OpenBSD__) && defined(OpenBSD)
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#if OpenBSD >= 509
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if (pledge("stdio", NULL) == -1)
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err(errno, "pledge");
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#endif
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#endif
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memset(&st, 0, sizeof(st));
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while ((c = getopt(argc, argv, "d")) != -1) {
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if (c != 'd')
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usage();
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st.debug = 1;
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break;
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||||||
}
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||||||
/* fallback in case tone detection fails */
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st.freq_min = 100000;
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st.freq_max = 0;
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st.freq_threshold = FREQ_DATA_THRESHOLD;
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/*
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* Used for separator calibration
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*/
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st.sep_min = FREQ_SEP_MIN;
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st.sep_max = FREQ_SEP_MAX;
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st.ascii_bit = 7;
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||||||
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st.ringpos = 0;
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st.sep_pos = SAMPLES_PER_FRAME;
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||||||
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if (host_is_big_endian())
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st.swap_bytes = 1;
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setvbuf(stdout, NULL, _IONBF, 0);
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for (;;)
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handle_audio(&st);
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||||||
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||||||
return EXIT_SUCCESS;
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|
||||||
}
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||||||
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||||||
static int
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|
||||||
host_is_big_endian(void)
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|
||||||
{
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||||||
unsigned int x = 1;
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return (*(unsigned char *)&x == 0);
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|
||||||
}
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||||||
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|
||||||
static void
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|
||||||
handle_audio(struct decoder_state *st)
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|
||||||
{
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|
||||||
int sample;
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||||||
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||||||
/*
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|
||||||
* If the modem signal disappears for several (read: 3)
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||||||
* frames, discard the partially assembled character.
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|
||||||
*/
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||||||
if (st->sample_count >= (3 * SAMPLES_PER_FRAME) ||
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|
||||||
st->freq_separator <= 0)
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||||||
reset_char(st);
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||||||
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|
||||||
st->sample_count = 0;
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||||||
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||||||
/* process exactly one frame */
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||||||
for (sample = 0; sample < SAMPLES_PER_FRAME; sample++)
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decode_pulse(st);
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|
||||||
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||||||
select_separator_tone(st);
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|
||||||
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|
||||||
if (set_ascii_bit(st) < 0)
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|
||||||
print_char(st);
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|
||||||
|
|
||||||
/* Detect tone per each frame */
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|
||||||
detect_tone(st);
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|
||||||
}
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|
||||||
|
|
||||||
/*
|
|
||||||
* collect separator tone statistics
|
|
||||||
* (and auto-adjust tolerances)
|
|
||||||
*/
|
|
||||||
static void
|
|
||||||
select_separator_tone(struct decoder_state *st)
|
|
||||||
{
|
|
||||||
int avg;
|
|
||||||
|
|
||||||
if (!is_valid_signal(st))
|
|
||||||
return;
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|
||||||
|
|
||||||
st->sep_sum += st->freq_separator;
|
|
||||||
st->sep_samples++;
|
|
||||||
|
|
||||||
if (st->sep_samples != 50)
|
|
||||||
return;
|
|
||||||
|
|
||||||
avg = st->sep_sum / st->sep_samples;
|
|
||||||
|
|
||||||
st->sep_min = avg - SEP_TOLERANCE_PULSES;
|
|
||||||
st->sep_max = avg + SEP_TOLERANCE_PULSES;
|
|
||||||
|
|
||||||
/* reset calibration accumulators */
|
|
||||||
st->sep_sum = 0;
|
|
||||||
st->sep_samples = 0;
|
|
||||||
|
|
||||||
if (st->debug)
|
|
||||||
printf("separator calibrated: %dHz\n",
|
|
||||||
avg * FRAME_RATE);
|
|
||||||
}
|
|
||||||
|
|
||||||
/*
|
|
||||||
* 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
|
|
||||||
is_valid_signal(struct decoder_state *st)
|
|
||||||
{
|
|
||||||
if (st->freq_data <= 0)
|
|
||||||
return 0;
|
|
||||||
|
|
||||||
if (st->freq_separator < st->sep_min ||
|
|
||||||
st->freq_separator > st->sep_max)
|
|
||||||
return 0;
|
|
||||||
|
|
||||||
return 1;
|
|
||||||
}
|
|
||||||
|
|
||||||
/*
|
|
||||||
* 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 (!is_valid_signal(st))
|
|
||||||
return st->ascii_bit;
|
|
||||||
|
|
||||||
if (st->freq_data < st->freq_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
|
|
||||||
reset_char(struct decoder_state *st)
|
|
||||||
{
|
|
||||||
st->ascii = 0;
|
|
||||||
st->ascii_bit = 7;
|
|
||||||
}
|
|
||||||
|
|
||||||
/*
|
|
||||||
* 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;
|
|
||||||
signed short sample;
|
|
||||||
int ringpos;
|
|
||||||
int sep_pos;
|
|
||||||
int diff_edge;
|
|
||||||
int diff_amp;
|
|
||||||
|
|
||||||
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);
|
|
||||||
|
|
||||||
/*
|
|
||||||
* Avoid startup edge. Since
|
|
||||||
* it's zero at startup, this
|
|
||||||
* may wrongly produce a pulse
|
|
||||||
*/
|
|
||||||
if (st->sample_count == 0)
|
|
||||||
st->prev_sample = sample;
|
|
||||||
|
|
||||||
/*
|
|
||||||
* Detect edges instead of amplitude.
|
|
||||||
* This is more tolerant of weak microphones
|
|
||||||
* and speaker distortion..
|
|
||||||
*
|
|
||||||
* However, we check both slope edges and
|
|
||||||
* amplitude, to mitagate noise.
|
|
||||||
*/
|
|
||||||
diff_amp = sample;
|
|
||||||
diff_edge = sample - st->prev_sample;
|
|
||||||
if (diff_edge < 0)
|
|
||||||
diff_edge = -diff_edge;
|
|
||||||
if (diff_amp < 0)
|
|
||||||
diff_amp = -diff_amp;
|
|
||||||
if (diff_edge > THRESHOLD &&
|
|
||||||
diff_amp > THRESHOLD)
|
|
||||||
new_pulse = 1;
|
|
||||||
else
|
|
||||||
new_pulse = 0;
|
|
||||||
st->prev_sample = sample;
|
|
||||||
|
|
||||||
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.
|
|
||||||
*/
|
|
||||||
if (++ringpos >= MAX_SAMPLES)
|
|
||||||
ringpos = 0;
|
|
||||||
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)
|
|
||||||
{
|
|
||||||
signed short sample;
|
|
||||||
unsigned short u;
|
|
||||||
|
|
||||||
while (st->inpos >= st->inlen)
|
|
||||||
read_words(st);
|
|
||||||
|
|
||||||
sample = st->inbuf[st->inpos++];
|
|
||||||
|
|
||||||
if (st->swap_bytes) {
|
|
||||||
u = (unsigned short)sample;
|
|
||||||
u = (u >> 8) | (u << 8);
|
|
||||||
|
|
||||||
sample = (signed short)u;
|
|
||||||
}
|
|
||||||
|
|
||||||
return sample;
|
|
||||||
}
|
|
||||||
|
|
||||||
static void
|
|
||||||
read_words(struct decoder_state *st)
|
|
||||||
{
|
|
||||||
size_t n;
|
|
||||||
|
|
||||||
n = fread(st->inbuf, sizeof(st->inbuf[0]),
|
|
||||||
READ_BUF, stdin);
|
|
||||||
|
|
||||||
if (n != 0) {
|
|
||||||
st->inpos = 0;
|
|
||||||
st->inlen = n;
|
|
||||||
|
|
||||||
return;
|
|
||||||
}
|
|
||||||
|
|
||||||
if (ferror(stdin))
|
|
||||||
err(errno, "stdin read");
|
|
||||||
if (feof(stdin))
|
|
||||||
exit(EXIT_SUCCESS);
|
|
||||||
}
|
|
||||||
|
|
||||||
/*
|
|
||||||
* Automatically detect spkmodem tone
|
|
||||||
*/
|
|
||||||
static void
|
|
||||||
detect_tone(struct decoder_state *st)
|
|
||||||
{
|
|
||||||
if (st->learn_frames >= LEARN_FRAMES)
|
|
||||||
return;
|
|
||||||
|
|
||||||
st->learn_frames++;
|
|
||||||
|
|
||||||
if (silent_signal(st))
|
|
||||||
return;
|
|
||||||
|
|
||||||
select_low_tone(st);
|
|
||||||
|
|
||||||
if (st->learn_frames != LEARN_FRAMES)
|
|
||||||
return;
|
|
||||||
|
|
||||||
/*
|
|
||||||
* If the observed frequencies are too close,
|
|
||||||
* learning likely failed (only one tone seen).
|
|
||||||
* Keep the default threshold.
|
|
||||||
*/
|
|
||||||
if (st->freq_max - st->freq_min < 2)
|
|
||||||
return;
|
|
||||||
|
|
||||||
st->freq_threshold =
|
|
||||||
(st->freq_min + st->freq_max) / 2;
|
|
||||||
|
|
||||||
if (st->debug)
|
|
||||||
printf("auto threshold: %dHz\n",
|
|
||||||
st->freq_threshold * FRAME_RATE);
|
|
||||||
}
|
|
||||||
|
|
||||||
/*
|
|
||||||
* Ignore silence / near silence.
|
|
||||||
* Both FIR windows will be near zero when no signal exists.
|
|
||||||
*/
|
|
||||||
static int
|
|
||||||
silent_signal(struct decoder_state *st)
|
|
||||||
{
|
|
||||||
return (st->freq_data <= 2 &&
|
|
||||||
st->freq_separator <= 2);
|
|
||||||
}
|
|
||||||
|
|
||||||
/*
|
|
||||||
* Choose the lowest active tone.
|
|
||||||
* Separator frames carry tone in the separator window,
|
|
||||||
* data frames carry tone in the data window.
|
|
||||||
*/
|
|
||||||
static void
|
|
||||||
select_low_tone(struct decoder_state *st)
|
|
||||||
{
|
|
||||||
int f;
|
|
||||||
|
|
||||||
f = st->freq_data;
|
|
||||||
|
|
||||||
if (f <= 0 || (st->freq_separator > 0 &&
|
|
||||||
st->freq_separator < f))
|
|
||||||
f = st->freq_separator;
|
|
||||||
|
|
||||||
if (f <= 0)
|
|
||||||
return;
|
|
||||||
|
|
||||||
if (f < st->freq_min)
|
|
||||||
st->freq_min = f;
|
|
||||||
|
|
||||||
if (f > st->freq_max)
|
|
||||||
st->freq_max = f;
|
|
||||||
}
|
|
||||||
|
|
||||||
static void
|
|
||||||
print_stats(struct decoder_state *st)
|
|
||||||
{
|
|
||||||
long pos;
|
|
||||||
|
|
||||||
int data_hz = st->freq_data * FRAME_RATE;
|
|
||||||
int sep_hz = st->freq_separator * FRAME_RATE;
|
|
||||||
int sep_hz_min = st->sep_min * FRAME_RATE;
|
|
||||||
int sep_hz_max = st->sep_max * FRAME_RATE;
|
|
||||||
|
|
||||||
if ((pos = ftell(stdin)) == -1) {
|
|
||||||
printf("%d %d %d data=%dHz sep=%dHz(min %dHz %dHz)\n",
|
|
||||||
st->freq_data,
|
|
||||||
st->freq_separator,
|
|
||||||
st->freq_threshold,
|
|
||||||
data_hz,
|
|
||||||
sep_hz,
|
|
||||||
sep_hz_min,
|
|
||||||
sep_hz_max);
|
|
||||||
return;
|
|
||||||
}
|
|
||||||
|
|
||||||
printf("%d %d %d @%ld data=%dHz sep=%dHz(min %dHz %dHz)\n",
|
|
||||||
st->freq_data,
|
|
||||||
st->freq_separator,
|
|
||||||
st->freq_threshold,
|
|
||||||
pos - SAMPLE_OFFSET,
|
|
||||||
data_hz,
|
|
||||||
sep_hz,
|
|
||||||
sep_hz_min,
|
|
||||||
sep_hz_max);
|
|
||||||
}
|
|
||||||
|
|
||||||
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;
|
|
||||||
}
|
|
||||||
@@ -0,0 +1 @@
|
|||||||
|
spkmodem-recv
|
||||||
@@ -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
|
||||||
@@ -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));
|
||||||
|
}
|
||||||
Reference in New Issue
Block a user