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/*---------------------------------------------------------------------------*\
FILE........: freedv_datac1_tx.c
AUTHOR......: David Rowe
DATE CREATED: April 2021
Demonstrates transmitting frames of raw data bytes using the FreeDV API datac1
mode. The data on stdin is transmitted as a sequence of modulated bursts.
Format of each burst: ...|preamble|data frame|postamble|silence|....
There is just one data frame per burst in this demo.
usage:
cd codec2/build_linux
head -c $((510*10)) </dev/urandom > binaryIn.bin
cat binaryIn.bin | ./demo/freedv_datac1_tx | ./demo/freedv_datac1_rx >
binaryOut.bin diff binaryIn.bin binaryOut.bin
Listen to the modulated Tx signal:
cat binaryIn.bin | ./demo/freedv_datac1_tx | aplay -f S16_LE
\*---------------------------------------------------------------------------*/
/*
Copyright (C) 2021 David Rowe
All rights reserved.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License version 2.1, as
published by the Free Software Foundation. This program is
distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
License for more details.
You should have received a copy of the GNU Lesser General Public License
along with this program; if not, see <http://www.gnu.org/licenses/>.
*/
#include <assert.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include "freedv_api.h"
int main(int argc, char *argv[]) {
struct freedv *freedv;
freedv = freedv_open(FREEDV_MODE_DATAC1);
assert(freedv != NULL);
size_t bytes_per_modem_frame = freedv_get_bits_per_modem_frame(freedv) / 8;
size_t payload_bytes_per_modem_frame =
bytes_per_modem_frame - 2; /* 16 bits used for the CRC */
size_t n_mod_out = freedv_get_n_tx_modem_samples(freedv);
uint8_t bytes_in[bytes_per_modem_frame];
short mod_out_short[n_mod_out];
for (int b = 0; b < 10; b++) {
/* send preamble */
int n_preamble = freedv_rawdatapreambletx(freedv, mod_out_short);
fwrite(mod_out_short, sizeof(short), n_preamble, stdout);
/* read our input data frame from stdin */
size_t nread =
fread(bytes_in, sizeof(uint8_t), payload_bytes_per_modem_frame, stdin);
if (nread != payload_bytes_per_modem_frame) break;
/* The raw data modes require a CRC in the last two bytes */
uint16_t crc16 = freedv_gen_crc16(bytes_in, payload_bytes_per_modem_frame);
bytes_in[bytes_per_modem_frame - 2] = crc16 >> 8;
bytes_in[bytes_per_modem_frame - 1] = crc16 & 0xff;
/* modulate and send a data frame */
freedv_rawdatatx(freedv, mod_out_short, bytes_in);
fwrite(mod_out_short, sizeof(short), n_mod_out, stdout);
/* send postamble */
int n_postamble = freedv_rawdatapostambletx(freedv, mod_out_short);
fwrite(mod_out_short, sizeof(short), n_postamble, stdout);
/* create some silence between bursts */
int inter_burst_delay_ms = 200;
int samples_delay = FREEDV_FS_8000 * inter_burst_delay_ms / 1000;
short sil_short[samples_delay];
for (int i = 0; i < samples_delay; i++) sil_short[i] = 0;
fwrite(sil_short, sizeof(short), samples_delay, stdout);
}
freedv_close(freedv);
return 0;
}
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