/* 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)); }