kopia lustrzana https://github.com/projecthorus/horusdemodlib
236 wiersze
6.8 KiB
C
236 wiersze
6.8 KiB
C
/*---------------------------------------------------------------------------*\
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FILE........: drs232.c
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AUTHOR......: David Rowe
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DATE CREATED: March 2016
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Looks for a unique word in series of bits. When found, deframes a RS232
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encoded frame of bytes. Used for high bit rate Horus SSTV reception.
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Frame format:
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16 bytes 0x55 - 0xabcdef01 UW - 256 bytes of payload - 2 bytes CRC
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Each byte is encoded as a 10 bit RS232 serial word:
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0 LSB .... MSB 1
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Building:
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$ gcc drs232.c -o drs232 -Wall
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\*---------------------------------------------------------------------------*/
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/*
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Copyright (C) 2016 David Rowe
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All rights reserved.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License version 2.1, as
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published by the Free Software Foundation. This program is
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distributed in the hope that it will be useful, but WITHOUT ANY
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WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
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License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with this program; if not, see <http://www.gnu.org/licenses/>.
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*/
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#include <assert.h>
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#include <stdlib.h>
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#include <errno.h>
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#include <stdio.h>
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#include <string.h>
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#include <stdint.h>
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/* states -----------------------------------------------*/
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#define LOOK_FOR_UW 0
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#define COLLECT_PACKET 1
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/* packet parameters */
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#define UW_BYTES 4
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#define UW_BITS 40
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#define UW_ALLOWED_ERRORS 5
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#define BYTES_PER_PACKET 256
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#define CRC_BYTES 2
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#define BITS_PER_BYTE 10
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#define UNPACKED_PACKET_BYTES ((UW_BYTES+BYTES_PER_PACKET+CRC_BYTES)*BITS_PER_BYTE)
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/* UW pattern we look for, including start/stop bits */
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uint8_t uw[] = {
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/* 0xb 0xa */
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0, 1, 1, 0, 1, 0, 1, 0, 1, 1,
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/* 0xd 0xc */
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0, 1, 0, 1, 1, 0, 0, 1, 1, 1,
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/* 0xf 0xe */
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0, 1, 1, 1, 1, 0, 1, 1, 1, 1,
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/* 0x1 0x0 */
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0, 1, 0, 0, 0, 0, 0, 0, 0, 1,
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};
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// from http://stackoverflow.com/questions/10564491/function-to-calculate-a-crc16-checksum
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unsigned short gen_crc16(unsigned char* data_p, int length){
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unsigned char x;
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unsigned short crc = 0xFFFF;
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while (length--){
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x = crc >> 8 ^ *data_p++;
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x ^= x>>4;
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crc = (crc << 8) ^ ((unsigned short)(x << 12)) ^ ((unsigned short)(x <<5)) ^ ((unsigned short)x);
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}
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return crc;
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}
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int main(int argc, char *argv[]) {
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FILE *fin, *fout;
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int state, next_state, i, j, k, ind, score, bits_read;
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char bit;
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uint8_t unpacked_packet[UNPACKED_PACKET_BYTES];
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uint8_t packet[BYTES_PER_PACKET+CRC_BYTES];
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uint8_t abyte;
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uint16_t tx_checksum, rx_checksum;
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int verbose, packet_errors, packets;
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if (argc < 3) {
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fprintf(stderr, "usage: drs232 InputOneBitPerChar OutputPackets [-v[v]]\n");
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exit(1);
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}
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if (strcmp(argv[1], "-") == 0) fin = stdin;
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else if ( (fin = fopen(argv[1],"rb")) == NULL ) {
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fprintf(stderr, "Error opening input file: %s: %s.\n",
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argv[1], strerror(errno));
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exit(1);
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}
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if (strcmp(argv[2], "-") == 0) fout = stdout;
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else if ( (fout = fopen(argv[2],"wb")) == NULL ) {
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fprintf(stderr, "Error opening output file: %s: %s.\n",
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argv[2], strerror(errno));
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exit(1);
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}
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verbose = 0;
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if (argc > 3) {
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if (strcmp(argv[3], "-v") == 0) {
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verbose = 1;
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}
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if (strcmp(argv[3], "-vv") == 0) {
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verbose = 2;
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}
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}
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state = LOOK_FOR_UW;
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for(i=0; i<UNPACKED_PACKET_BYTES; i++)
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unpacked_packet[i] = 0;
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bits_read = 0;
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packet_errors = packets = 0;
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while(fread(&bit, sizeof(char), 1, fin) == 1) {
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bits_read++;
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next_state = state;
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if (state == LOOK_FOR_UW) {
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/* put latest input bit into sliding buffer */
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for(i=0; i<UW_BITS-1; i++) {
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unpacked_packet[i] = unpacked_packet[i+1];
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}
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unpacked_packet[i] = bit;
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/* lets see if it matches the UW */
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score = 0;
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for(i=0; i<UW_BITS; i++) {
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score += (unpacked_packet[i] == uw[i]);
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/* if (i == BITS_PER_BYTE)
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printf(" ");
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printf("%1d", unpacked_packet[i]); */
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}
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//printf("\n");
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//fprintf(stderr,"UW score: %d\n", score);
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if (score > (UW_BITS-UW_ALLOWED_ERRORS)) {
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if (verbose == 2) {
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fprintf(stderr,"UW found!\n");
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}
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ind = UW_BITS;
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next_state = COLLECT_PACKET;
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}
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}
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if (state == COLLECT_PACKET) {
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unpacked_packet[ind++] = bit;
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if (ind == UNPACKED_PACKET_BYTES) {
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/* OK we have enough bits, remove RS232 sync bits and pack */
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for(i=UW_BITS,k=0; i<UNPACKED_PACKET_BYTES; i+=BITS_PER_BYTE,k++) {
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//for(j=0; j<BITS_PER_BYTE; j++)
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// printf("%1d", unpacked_packet[i+j]);
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//printf("\n");
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abyte = 0;
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for(j=0; j<8; j++) {
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abyte |= unpacked_packet[i+j+1] << j;
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}
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packet[k] = abyte;
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//printf("k:%d 0x%02x\n", k, packet[k]);
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//if (k == 4)
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// exit(0);
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}
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/* output if CRC check is OK */
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rx_checksum = gen_crc16(packet, BYTES_PER_PACKET);
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tx_checksum = packet[BYTES_PER_PACKET] + (packet[BYTES_PER_PACKET+1] << 8);
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if (verbose == 2) {
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fprintf(stderr, "k=%d bytes after UW tx_checksum: 0x%02x rx_checksum: 0x%02x\n",
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k, tx_checksum, rx_checksum);
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}
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packets++;
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if (rx_checksum == tx_checksum) {
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fwrite(packet, sizeof(char), BYTES_PER_PACKET, fout);
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}
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else
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packet_errors++;
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if (verbose) {
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fprintf(stderr, "packets: %d packet_errors: %d PER: %4.3f\n",
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packets, packet_errors,
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(float)packet_errors/packets);
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}
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next_state = LOOK_FOR_UW;
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}
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}
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//if (bits_read == (16*10 + UNPACKED_PACKET_BYTES))
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// exit(0);
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state = next_state;
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}
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fclose(fin);
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fclose(fout);
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fprintf(stderr, "packets: %d packet_errors: %d PER: %4.3f\n", packets, packet_errors,
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(float)packet_errors/packets);
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return 0;
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}
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