--- /dev/null
+/*---------------------------------------------------------------------------*\
+
+ FILE........: drs232_ldpc.c
+ AUTHOR......: David Rowe
+ DATE CREATED: Sep 2016
+
+ Looks for a unique word in series of soft decision symbols. When
+ found, deframes a RS232 encoded frame of soft decision bit, LDPC
+ decodes, and outputs a frame of packed bytes. Used for high biit
+ rate Horus SSTV reception.
+
+ Frame format:
+
+ 16 bytes 0x55 - 0xabcd UW - 256 bytes of payload - 2 bytes CRC - 65 bytes LPDC Parity
+
+ Each byte is encoded as a 10 bit RS232 serial word:
+
+ 0 LSB .... MSB 1
+
+ Building:
+
+ $ gcc drs232_ldpc.c mpdecode_core.c -o drs232_ldpc -Wall -lm
+
+\*---------------------------------------------------------------------------*/
+
+
+/*
+ Copyright (C) 2016 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 <stdlib.h>
+#include <errno.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdint.h>
+
+#include "mpdecode_core.h"
+
+/* Machine generated consts, H_rows, H_cols, test input/output data to
+ change LDPC code regenerate this file. */
+
+#include "H2064_516_sparse.h"
+
+/* states -----------------------------------------------*/
+
+#define LOOK_FOR_UW 0
+#define COLLECT_PACKET 1
+
+/* packet parameters */
+
+#define UW_BYTES 2
+#define UW_BITS 20
+#define BYTES_PER_PACKET 256
+#define CRC_BYTES 2
+#define PARITY_BYTES 65
+#define BITS_PER_BYTE 10
+#define UNPACKED_PACKET_BYTES ((UW_BYTES+BYTES_PER_PACKET+CRC_BYTES)*BITS_PER_BYTE)
+#define SYMBOLS_PER_PACKET (BYTES_PER_PACKET+CRC_BYTES+PARITY_BYTES)*BITS_PER_BYTE
+
+/* UW pattern we look for, including start/stop bits */
+
+uint8_t uw[] = {
+ /* 0xb 0xa */
+ 0, 1, 1, 0, 1, 0, 1, 0, 1, 1,
+ /* 0xd 0xc */
+ 0, 1, 0, 1, 1, 0, 0, 1, 1, 1,
+};
+
+
+// from http://stackoverflow.com/questions/10564491/function-to-calculate-a-crc16-checksum
+
+unsigned short gen_crc16(unsigned char* data_p, int length){
+ unsigned char x;
+ unsigned short crc = 0xFFFF;
+
+ while (length--){
+ x = crc >> 8 ^ *data_p++;
+ x ^= x>>4;
+ crc = (crc << 8) ^ ((unsigned short)(x << 12)) ^ ((unsigned short)(x <<5)) ^ ((unsigned short)x);
+ }
+
+ return crc;
+}
+
+
+int main(int argc, char *argv[]) {
+ FILE *fin, *fout;
+ int state, next_state, i, j, k, ind, score;
+ float symbol;
+ uint8_t bit, bit_buffer[UW_BITS];
+ double symbol_buf[SYMBOLS_PER_PACKET];
+ double symbol_buf_no_rs232[SYMBOLS_PER_PACKET];
+ double llr[SYMBOLS_PER_PACKET];
+ char unpacked_packet[CODELENGTH];
+ uint8_t packet[BYTES_PER_PACKET+CRC_BYTES];
+ uint8_t abyte;
+ uint16_t tx_checksum, rx_checksum, packet_errors, packets;
+ int CodeLength;
+ struct LDPC ldpc;
+
+ /* LDPC parameters */
+
+ CodeLength = CODELENGTH; /* length of entire codeword in bits */
+
+ /* set up LDPC code from include file constants */
+
+ ldpc.max_iter = MAX_ITER;
+ ldpc.dec_type = 0;
+ ldpc.q_scale_factor = 1;
+ ldpc.r_scale_factor = 1;
+ ldpc.CodeLength = CODELENGTH;
+ ldpc.NumberParityBits = NUMBERPARITYBITS;
+ ldpc.NumberRowsHcols = NUMBERROWSHCOLS;
+ ldpc.max_row_weight = MAX_ROW_WEIGHT;
+ ldpc.max_col_weight = MAX_COL_WEIGHT;
+ ldpc.H_rows = H_rows;
+ ldpc.H_cols = H_cols;
+
+ /* process command line ----------------------------------------------*/
+
+ if (argc < 3) {
+ fprintf(stderr, "usage: drs232 InputOneSymbolPerFloat OutputPackets\n");
+ exit(1);
+ }
+
+ if (strcmp(argv[1], "-") == 0) fin = stdin;
+ else if ( (fin = fopen(argv[1],"rb")) == NULL ) {
+ fprintf(stderr, "Error opening input file: %s: %s.\n",
+ argv[2], strerror(errno));
+ exit(1);
+ }
+
+ if (strcmp(argv[2], "-") == 0) fout = stdout;
+ else if ( (fout = fopen(argv[2],"wb")) == NULL ) {
+ fprintf(stderr, "Error opening output file: %s: %s.\n",
+ argv[3], strerror(errno));
+ exit(1);
+ }
+
+ state = LOOK_FOR_UW;
+ for(i=0; i<UNPACKED_PACKET_BYTES; i++)
+ bit_buffer[i] = 0;
+
+ packet_errors = packets = 0;
+
+ while(fread(&symbol, sizeof(float), 1, fin) == 1) {
+
+ /* make hard decision for purpose of UW detection */
+
+ bit = symbol < 0;
+ //printf("symbol; %f bit: %d\n", symbol, bit);
+ if (state == LOOK_FOR_UW) {
+
+ /* put latest input bit into sliding buffer */
+
+ for(i=0; i<UW_BITS-1; i++) {
+ bit_buffer[i] = bit_buffer[i+1];
+ }
+ bit_buffer[i] = bit;
+
+ /* lets see if it matches the UW */
+
+ score = 0;
+ for(i=0; i<UW_BITS; i++) {
+ score += (bit_buffer[i] == uw[i]);
+ /* if (i == BITS_PER_BYTE)
+ printf(" ");
+ printf("%1d", unpacked_packet[i]); */
+ }
+ //printf("\n");
+
+ //fprintf(stderr,"UW score: %d\n", score);
+ if (score == UW_BITS) {
+ fprintf(stderr,"UW found!\n");
+ ind = 0;
+ next_state = COLLECT_PACKET;
+ }
+ }
+
+ if (state == COLLECT_PACKET) {
+ symbol_buf[ind++] = symbol;
+
+ if (ind == SYMBOLS_PER_PACKET) {
+
+ /* OK we have enough bits, remove RS232 sync symbols */
+
+ for(i=0,k=0; i<SYMBOLS_PER_PACKET; i+=BITS_PER_BYTE) {
+ for(j=0; j<8; j++) {
+ symbol_buf_no_rs232[k+j] = symbol_buf[i+j+1];
+ }
+ k += 8;
+ }
+ printf("k: %d CodeLength: %d\n", k, CodeLength);
+
+ /* now LDPC decode */
+
+ sd_to_llr(llr, symbol_buf_no_rs232, CodeLength);
+ run_ldpc_decoder(&ldpc, unpacked_packet, llr);
+
+ /* pack into bytes */
+
+ for(i=0; i<BYTES_PER_PACKET+CRC_BYTES; i++) {
+ abyte = 0;
+ for(j=0; j<8; j++)
+ abyte |= unpacked_packet[8*i+j] << j;
+ packet[i] = abyte;
+ }
+
+ /* then output if CRC check is OK */
+
+ rx_checksum = gen_crc16(packet, BYTES_PER_PACKET);
+ tx_checksum = packet[BYTES_PER_PACKET] + (packet[BYTES_PER_PACKET+1] << 8);
+
+ fprintf(stderr, "tx_checksum: 0x%02x rx_checksum: 0x%02x\n", tx_checksum, rx_checksum);
+
+ packets++;
+ if (rx_checksum == tx_checksum) {
+ fwrite(packet, sizeof(char), BYTES_PER_PACKET, fout);
+ }
+ else
+ packet_errors++;
+
+ next_state = LOOK_FOR_UW;
+ }
+
+ }
+ //if (bits_read == (16*10 + UNPACKED_PACKET_BYTES))
+ // exit(0);
+
+ state = next_state;
+ }
+
+ fclose(fin);
+ fclose(fout);
+
+ fprintf(stderr, "packets: %d packet_errors: %d PER: %4.3f\n", packets, packet_errors,
+ (float)packet_errors/packets);
+
+ return 0;
+}
+
+
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