diff options
| -rw-r--r-- | util/spkmodem_decode/spkmodem-decode.c | 209 |
1 files changed, 114 insertions, 95 deletions
diff --git a/util/spkmodem_decode/spkmodem-decode.c b/util/spkmodem_decode/spkmodem-decode.c index 44b8e084..a5283e51 100644 --- a/util/spkmodem_decode/spkmodem-decode.c +++ b/util/spkmodem_decode/spkmodem-decode.c @@ -209,25 +209,44 @@ struct decoder_state { static const char *argv0; +/* + * 16-bit little endian words are read + * continuously. we will swap them, if + * the host cpu is big endian. + */ static int host_is_big_endian(void); + +/* main loop */ static void handle_audio(struct decoder_state *st); -static void detect_tone(struct decoder_state *st); -static int silent_signal(struct decoder_state *st); -static void select_low_tone(struct decoder_state *st); + +/* separate tone tolerances */ static void select_separator_tone(struct decoder_state *st); -static int valid_signal(struct decoder_state *st); +static int is_valid_signal(struct decoder_state *st); + +/* output to terminal */ +static int set_ascii_bit(struct decoder_state *st); +static void print_char(struct decoder_state *st); +static void reset_char(struct decoder_state *st); + +/* process samples/frames */ static void decode_pulse(struct decoder_state *st); static signed short read_sample(struct decoder_state *st); static void read_words(struct decoder_state *st); -static int set_ascii_bit(struct decoder_state *st); -static void print_char(struct decoder_state *st); + +/* continually adjust tone */ +static void detect_tone(struct decoder_state *st); +static int silent_signal(struct decoder_state *st); +static void select_low_tone(struct decoder_state *st); + +/* debug */ static void print_stats(struct decoder_state *st); -static void reset_char(struct decoder_state *st); +/* error handling / usage */ static void err(int errval, const char *msg, ...); static void usage(void); static const char *progname(void); +/* portability (old systems) */ int getopt(int, char * const *, const char *); extern char *optarg; extern int optind; @@ -318,70 +337,6 @@ handle_audio(struct decoder_state *st) } /* - * 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; - - 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; -} - -/* * collect separator tone statistics * (and auto-adjust tolerances) */ @@ -390,7 +345,7 @@ select_separator_tone(struct decoder_state *st) { int avg; - if (valid_signal(st)) + if (is_valid_signal(st)) return; if (st->sep_samples >= 50 && st->freq_separator <= 0) @@ -418,13 +373,47 @@ select_separator_tone(struct decoder_state *st) * from being misinterpreted as data. */ static int -valid_signal(struct decoder_state *st) +is_valid_signal(struct decoder_state *st) { return (st->freq_separator > 0 && st->freq_data > 0); } /* + * 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 < 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 @@ -547,30 +536,67 @@ read_words(struct decoder_state *st) } /* - * Each validated frame contributes one bit of modem data. - * Bits are accumulated MSB-first into the ASCII byte. + * Automatically detect spkmodem tone */ -static int -set_ascii_bit(struct decoder_state *st) +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; + + st->freq_threshold = + (st->freq_min + st->freq_max) / 2; + if (st->debug) - print_stats(st); - if (st->freq_data < st->freq_threshold) - st->ascii |= (1 << st->ascii_bit); + printf("auto threshold: %dHz\n", + st->freq_threshold * FRAME_RATE); +} - st->ascii_bit--; - return st->ascii_bit; +/* + * 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 -print_char(struct decoder_state *st) +select_low_tone(struct decoder_state *st) { - if (st->debug) - printf("<%c,%x>", st->ascii, st->ascii); - else - putchar(st->ascii); + int f; - reset_char(st); + 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 @@ -607,13 +633,6 @@ print_stats(struct decoder_state *st) } 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; |